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Gamain B, Smith JD, Viebig NK, Gysin J, Scherf A. Pregnancy-associated malaria: Parasite binding, natural immunity and vaccine development. Int J Parasitol 2007; 37:273-83. [PMID: 17224156 DOI: 10.1016/j.ijpara.2006.11.011] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2006] [Revised: 11/21/2006] [Accepted: 11/22/2006] [Indexed: 11/26/2022]
Abstract
Humans living in areas of high malaria transmission gradually acquire, during the early years of life, protective clinical immunity to Plasmodium falciparum, limiting serious complications of malaria to young children. However, pregnant women become more susceptible to severe P. falciparum infections during their first pregnancy. Pregnancy associated malaria is coupled with massive accumulation of parasitised erythrocytes and monocytes in the placental intervillous blood spaces, contributing to disease and death in pregnant women and developing infants. Indirect evidence suggests that prevention may be possible by vaccinating women of childbearing age before their first pregnancy. This review aims to introduce the reader to the implications of malaria infection during pregnancy and to analyse recent findings towards the identification and characterisation of parasite encoded erythrocyte surface proteins expressed in malaria-infected pregnant women that are likely targets of protective immunity and have potential for vaccine development.
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Affiliation(s)
- Benoît Gamain
- Unité de Biologie des Interactions Hôte-Parasite, Institut Pasteur and CNRS, Paris, France
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52
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Sharp S, Lavstsen T, Fivelman QL, Saeed M, McRobert L, Templeton TJ, Jensen ATR, Baker DA, Theander TG, Sutherland CJ. Programmed transcription of the var gene family, but not of stevor, in Plasmodium falciparum gametocytes. EUKARYOTIC CELL 2007; 5:1206-14. [PMID: 16896206 PMCID: PMC1539138 DOI: 10.1128/ec.00029-06] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The var genes encode Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) proteins, a set of highly diverse surface-expressed proteins that mediate adhesion of erythrocytes infected with asexual blood-stage parasites to host endothelium. Switching among expressed PfEMP1 variants in the course of a blood-stage infection is a key component of antigenic variation, and thus immune evasion, by the parasite. The majority of var loci are found in the subtelomeric regions of P. falciparum chromosomes associated with members of other multigene families, including stevor. Both PfEMP1 and STEVOR are expressed in gametocytes, the transmissible parasite stage, but the role of these proteins in the biology of sexual-stage parasites remains unknown. PfEMP1 may continue to mediate antigenic variation in gametocytes, which need to persist in the host for many days before reaching maturity. Using quantitative reverse transcription-PCR and Northern hybridization, we demonstrate that transcription of a defined subset of type C var loci occurs during gametocyte development in vitro. This transcriptional program occurs in gametocytes regardless of the var expression phenotype of their asexual progenitors and therefore is subject to regulatory processes distinct from those that manage antigenic variation in the asexual parasite. In contrast, the same stevor variants are transcribed in both gametocytes and their asexual progenitors. We also provide evidence that for both asexual parasites and gametocytes, var and stevor transcription patterns are not linked to each other.
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Affiliation(s)
- Sarah Sharp
- Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
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53
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Kraemer SM, Kyes SA, Aggarwal G, Springer AL, Nelson SO, Christodoulou Z, Smith LM, Wang W, Levin E, Newbold CI, Myler PJ, Smith JD. Patterns of gene recombination shape var gene repertoires in Plasmodium falciparum: comparisons of geographically diverse isolates. BMC Genomics 2007; 8:45. [PMID: 17286864 PMCID: PMC1805758 DOI: 10.1186/1471-2164-8-45] [Citation(s) in RCA: 147] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2006] [Accepted: 02/07/2007] [Indexed: 02/05/2023] Open
Abstract
Background Var genes encode a family of virulence factors known as PfEMP1 (Plasmodium falciparum erythrocyte membrane protein 1) which are responsible for both antigenic variation and cytoadherence of infected erythrocytes. Although these molecules play a central role in malaria pathogenesis, the mechanisms generating variant antigen diversification are poorly understood. To investigate var gene evolution, we compared the variant antigen repertoires from three geographically diverse parasite isolates: the 3D7 genome reference isolate; the recently sequenced HB3 isolate; and the IT4/25/5 (IT4) parasite isolate which retains the capacity to cytoadhere in vitro and in vivo. Results These comparisons revealed that only two var genes (var1csa and var2csa) are conserved in all three isolates and one var gene (Type 3 var) has homologs in IT4 and 3D7. While the remaining 50 plus genes in each isolate are highly divergent most can be classified into the three previously defined major groups (A, B, and C) on the basis of 5' flanking sequence and chromosome location. Repertoire-wide sequence comparisons suggest that the conserved homologs are evolving separately from other var genes and that genes in group A have diverged from other groups. Conclusion These findings support the existence of a var gene recombination hierarchy that restricts recombination possibilities and has a central role in the functional and immunological adaptation of var genes.
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Affiliation(s)
- Susan M Kraemer
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA 98109-5219, USA
| | - Sue A Kyes
- Molecular Parasitology Group, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
| | - Gautam Aggarwal
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA 98109-5219, USA
| | - Amy L Springer
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA 98109-5219, USA
| | - Siri O Nelson
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA 98109-5219, USA
| | - Zoe Christodoulou
- Molecular Parasitology Group, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
| | - Leia M Smith
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA 98109-5219, USA
| | - Wendy Wang
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA 98109-5219, USA
| | - Emily Levin
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA 98109-5219, USA
| | - Christopher I Newbold
- Molecular Parasitology Group, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
| | - Peter J Myler
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA 98109-5219, USA
- Department of Pathobiology, University of Washington, Seattle, WA 98195, USA
| | - Joseph D Smith
- Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA 98109-5219, USA
- Department of Pathobiology, University of Washington, Seattle, WA 98195, USA
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54
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Magistrado PA, Lusingu J, Vestergaard LS, Lemnge M, Lavstsen T, Turner L, Hviid L, Jensen ATR, Theander TG. Immunoglobulin G antibody reactivity to a group A Plasmodium falciparum erythrocyte membrane protein 1 and protection from P. falciparum malaria. Infect Immun 2007; 75:2415-20. [PMID: 17283085 PMCID: PMC1865733 DOI: 10.1128/iai.00951-06] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Variant surface antigens (VSA) on the surface of Plasmodium falciparum-infected red blood cells play a major role in the pathogenesis of malaria and are key targets for acquired immunity. The best-characterized VSA belong to the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family. In areas where P. falciparum is endemic, parasites causing severe malaria and malaria in young children with limited immunity tend to express semiconserved PfEMP1 molecules encoded by group A var genes. Here we investigated antibody responses of Tanzanians who were 0 to 19 years old to PF11_0008, a group A PfEMP1. PF11_0008 has previously been found to be highly transcribed in a nonimmune Dutch volunteer experimentally infected with NF54 parasites. A high proportion of the Tanzanian donors had antibodies against recombinant PF11_0008 domains, and in children who were 4 to 9 years old the presence of antibodies to the PF11_0008 CIDR2beta domain was associated with reduced numbers of malaria episodes. These results indicate that homologues of PF11_0008 are present in P. falciparum field isolates and suggest that PF11_0008 CIDR2beta-reactive antibodies might be involved in protection against malaria episodes.
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Affiliation(s)
- Pamela A Magistrado
- Centre for Medical Parasitology at Department of Medical Microbiology and Immunology, University of Copenhagen, Denmark.
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55
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Abstract
In recent years, the sequencing and annotation of complete genomes, together with the development of genetic and proteomic techniques to study previously intractable eukaryotic microbes, has revealed interesting new themes in the control of virulence gene expression. Families of variantly expressed genes are found adjacent to telomeres in the genomes of both pathogenic and non-pathogenic organisms. This subtelomeric DNA is normally heterochromatic and higher-order chromatin structure has now come to be recognized as an important factor controlling both the evolution and expression dynamics of these multigene families. In eukaryotic cells, higher-order chromatin structure plays a central role in many DNA processes including the control of chromosome integrity and recombination, DNA partitioning during cell division, and transcriptional control. DNA can be packaged in two distinct forms: euchromatin is relatively accessible to DNA binding proteins and generally contains active genes, while heterochromatin is densely packaged, relatively inaccessible and usually transcriptionally silent. These features of chromatin are epigenetically inherited from cell cycle to cell cycle. This review will focus on the epigenetic mechanisms used to control expression of virulence genes in medically important microbial pathogens. Examples of such control have now been reported in several evolutionarily distant species, revealing what may be a common strategy used to regulate many very different families of genes.
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Affiliation(s)
- Catherine J Merrick
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, 665 Huntington Ave, Building I, Rm 706, Boston, MA 02115, USA
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56
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Peters JM, Fowler EV, Krause DR, Cheng Q, Gatton ML. Differential changes in Plasmodium falciparum var transcription during adaptation to culture. J Infect Dis 2007; 195:748-55. [PMID: 17262719 PMCID: PMC1866257 DOI: 10.1086/511436] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2006] [Accepted: 10/02/2006] [Indexed: 11/03/2022] Open
Abstract
Plasmodium falciparum erythrocyte membrane protein 1, which is encoded by the var multigene family, is expressed on the surface of P. falciparum-infected erythrocytes and has been implicated in many of the complications associated with falciparum malaria. Transcriptional switching of var is commonly investigated using in vitro cultured parasites, because parasite material from patients is limited. We investigated the affect of short-term in vitro cultivation on var gene transcription in patient samples. A significant reduction in the overall abundance of var transcripts was observed during the first approximately 10 days of culture. The rate of down-regulation was not constant among all var genes; genes with an upsA, -D, and -E 5' flanking region had a significantly faster rate than genes with an upsB or -C flanking region. These results have significant implications for the investigation of associations between var transcription and clinical manifestations using parasites that have been enriched by in vitro culture.
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Affiliation(s)
- Jennifer M Peters
- Malaria Drug Resistance and Chemotherapy Laboratory, Queensland Institute of Medical Research, Herston, Australia
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57
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Kyes S, Christodoulou Z, Pinches R, Kriek N, Horrocks P, Newbold C. Plasmodium falciparum var
gene expression is developmentally controlled at the level of RNA polymerase II‐mediated transcription initiation. Mol Microbiol 2007; 63:1237-47. [PMID: 17257309 DOI: 10.1111/j.1365-2958.2007.05587.x] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The Plasmodium falciparum var gene family codes for a major virulence factor in this most lethal of human malaria parasites. A single var protein variant type is expressed on each infected red blood cell, with antigenic variation allowing progeny parasites to escape host immune detection. The control of mutually exclusive var gene expression in the parasite relies on in situ epigenetic changes. Whether control of expression occurs at transcription initiation or post transcription, however, remains to be established. Recent evidence supports existence of a unique var transcription site at the nuclear periphery containing the dominantly expressed var gene, although silent var genes can colocalize to the same region. We demonstrate here that exclusive var gene expression is controlled at the level of transcription initiation during ring stages and that var genes are transcribed by RNA polymerase II. This represents another example where P. falciparum differs from the paradigm for antigenic variation, Trypanosoma brucei.
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Affiliation(s)
- Sue Kyes
- Weatherall Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital, Headington, Oxford, UK.
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58
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Albrecht L, Merino EF, Hoffmann EHE, Ferreira MU, de Mattos Ferreira RG, Osakabe AL, Dalla Martha RC, Ramharter M, Durham AM, Ferreira JE, Del Portillo HA, Wunderlich G. Extense variant gene family repertoire overlap in Western Amazon Plasmodium falciparum isolates. Mol Biochem Parasitol 2006; 150:157-65. [PMID: 16938359 DOI: 10.1016/j.molbiopara.2006.07.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2005] [Revised: 07/04/2006] [Accepted: 07/17/2006] [Indexed: 11/29/2022]
Abstract
In order to find a molecular basis for observations of relatively fast developing immunity to malarial infections in the Western Amazon region, the partial var, stevor and rif gene repertoires of nine different Plasmodium falciparum isolates collected in 1985 and 2000-2004 were evaluated. In contrast to previous results from South East Asia, the variant gene repertoire in Brazilian isolates is rather small and redundant. While the individual var repertoire sizes of Brazilian strains did not differ from Southeast Asian/African isolates, we found an over three times higher overlap of var sequence repertoires in Amazonian strains which was also conserved over time, suggesting the ongoing circulation of a similar var gene repertoire. Coincidently, almost 40% of the sequences identified herein showed the highest degree of similarity to var genes from either Brazilian or Venezuelan isolates, indicating a limited var repertoire of P. falciparum in the Amazon Basin as a whole. The intrastrain similarities of var genes were slightly but significantly lower than in Southeast Asian/African samples suggesting a higher selective pressure for diversification in Amazonian isolates. Despite of higher copy numbers per genome, rif genes also showed a significant repertoire overlap. stevor genes, which share the same predominant subtelomeric localization as var and rif genes, showed a still higher repertoire overlap and were highly similar to 3D7 stevor genes, indicating stronger functional conservation than var and rif genes. This is the first study that reveals that P. falciparum variant gene repertoires of certain areas can be limited. This has important implications for the strain-specific immunity against variant antigens occurring in these areas.
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Affiliation(s)
- Letusa Albrecht
- Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
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59
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Kyriacou HM, Stone GN, Challis RJ, Raza A, Lyke KE, Thera MA, Koné AK, Doumbo OK, Plowe CV, Rowe JA. Differential var gene transcription in Plasmodium falciparum isolates from patients with cerebral malaria compared to hyperparasitaemia. Mol Biochem Parasitol 2006; 150:211-8. [PMID: 16996149 PMCID: PMC2176080 DOI: 10.1016/j.molbiopara.2006.08.005] [Citation(s) in RCA: 145] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2006] [Revised: 08/04/2006] [Accepted: 08/08/2006] [Indexed: 11/13/2022]
Abstract
The Plasmodium falciparum variant erythrocyte surface antigens known as PfEMP1, encoded by the var gene family, are thought to play a crucial role in malaria pathogenesis because they mediate adhesion to host cells and immuno-modulation. Var genes have been divided into three major groups (A, B and C) and two intermediate groups (B/A and B/C) on the basis of their genomic location and upstream sequence. We analysed expressed sequence tags of the var gene DBLα domain to investigate var gene transcription in relation to disease severity in Malian children. We found that P. falciparum isolates from children with cerebral malaria (unrousable coma) predominantly transcribe var genes with DBLα1-like domains that are characteristic of Group A or B/A var genes. In contrast, isolates from children with equally high parasite burdens but no symptoms or signs of severe malaria (hyperparasitaemia patients) predominantly transcribe var genes with DBLα0-like domains that are characteristic of the B and C-related var gene groups. These results suggest that var genes with DBLα1-like domains (Group A or B/A) may be implicated in the pathogenesis of cerebral malaria, while var genes with DBLα0-like domains promote less virulent malaria infections.
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Affiliation(s)
- Helen M. Kyriacou
- Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, UK
| | - Graham N. Stone
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, UK
| | - Richard J. Challis
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, UK
| | - Ahmed Raza
- Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, UK
| | - Kirsten E. Lyke
- University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Mahamadou A. Thera
- Malaria Research and Training Centre, Faculty of Medicine, Pharmacy and Dentistry, University of Bamako, Bamako, BP 1805, Mali
| | - Abdoulaye K. Koné
- Malaria Research and Training Centre, Faculty of Medicine, Pharmacy and Dentistry, University of Bamako, Bamako, BP 1805, Mali
| | - Ogobara K. Doumbo
- Malaria Research and Training Centre, Faculty of Medicine, Pharmacy and Dentistry, University of Bamako, Bamako, BP 1805, Mali
| | | | - J. Alexandra Rowe
- Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, UK
- Corresponding address: Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, UK. Tel.: +44 131 650 5492; fax: +44 131 650 6564.
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60
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Duffy MF, Caragounis A, Noviyanti R, Kyriacou HM, Choong EK, Boysen K, Healer J, Rowe JA, Molyneux ME, Brown GV, Rogerson SJ. Transcribed var genes associated with placental malaria in Malawian women. Infect Immun 2006; 74:4875-83. [PMID: 16861676 PMCID: PMC1539630 DOI: 10.1128/iai.01978-05] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Determining the diversity of PfEMP1 sequences expressed by Plasmodium falciparum-infected erythrocytes isolated from placentas is important for attempts to develop a pregnancy-specific malaria vaccine. The DBLgamma and var2csa DBL3x domains of PfEMP1 molecules are believed to mediate placental sequestration of infected erythrocytes, so the sequences encoding these domains were amplified from the cDNAs of placental parasites by using degenerate oligonucleotides. The levels of specific var cDNAs were then determined by quantitative reverse transcription-PCR. Homologues of var2csa DBL3x were the predominant sequences amplified from the cDNAs of most placental but not most children's parasites. There was 56% identity between all placental var2csa sequences. Many different DBLgamma domains were amplified from the cDNAs of placental and children's isolates. var2csa transcripts were the most abundant var transcripts of those tested in 11 of 12 placental isolates and 1 of 6 children's isolates. Gravidity did not affect the levels of var2csa transcripts. We concluded that placental malaria is frequently associated with transcription of var2csa but that other var genes are also expressed, and parasites expressing high levels of var2csa are not restricted to pregnant women. The diversity of var2csa sequences may be important for understanding immunity and for the development of vaccines for malaria during pregnancy.
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Affiliation(s)
- Michael F Duffy
- Department of Medicine (RMH), University of Melbourne, Post Office, Royal Melbourne Hospital, Victoria 3050, Australia.
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61
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Fowler EV, Chavchich M, Chen N, Peters JM, Kyle DE, Gatton ML, Cheng Q. Physical linkage to drug resistance genes results in conservation of var genes among West Pacific Plasmodium falciparum isolates. J Infect Dis 2006; 194:939-48. [PMID: 16960782 PMCID: PMC1564382 DOI: 10.1086/506619] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2006] [Accepted: 04/10/2006] [Indexed: 11/03/2022] Open
Abstract
The multicopy var gene family encoding the variant surface antigen Plasmodium falciparum erythrocyte membrane protein 1 is highly diverse, with little overlap between different P. falciparum isolates. We report 5 var genes (varS1-varS5) that are shared at relatively high frequency among 63 genetically diverse P. falciparum isolates collected from 5 islands in the West Pacific region. The varS1, varS2, and varS3 genes were localized to the internal region on chromosome 4, approximately 200 kb from pfdhfr-ts, whereas varS4 and varS5 were mapped to an internal region of chromosome 7, within 100 kb of pfcrt. The presence of varS2 and varS3 were significantly correlated with the pyrimethamine-resistant pfdhfr genotype, whereas varS4 was strongly correlated with the chloroquine-resistant pfcrt genotype. Thus, the conservation of these var genes is the result of their physical linkage with drug-resistant genes in combination with the antimalarial drug pressure in the region.
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Affiliation(s)
- Elizabeth V Fowler
- Drug Resistance and Diagnostics, Australian Army Malaria Institute, Brisbane, Australia
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62
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Fernandez-Becerra C, Pein O, de Oliveira TR, Yamamoto MM, Cassola AC, Rocha C, Soares IS, de Bragança Pereira CA, del Portillo HA. Variant proteins of Plasmodium vivax are not clonally expressed in natural infections. Mol Microbiol 2006; 58:648-58. [PMID: 16238616 DOI: 10.1111/j.1365-2958.2005.04850.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Plasmodium vivax is the most widely distributed human malaria parasite and responsible for 70-80 million clinical cases each year and a large socio-economical burden. The sequence of a chromosome end from P. vivax revealed the existence of a multigene superfamily, termed vir (P. vivax variant antigens), that can be subdivided into different subfamilies based on sequence similarity analysis and which represents close to 10-20% of the coding sequences of the parasite. Here we show that there is a vast repertoire of vir genes abundantly expressed in isolates obtained from human patients, that different vir gene subfamilies are transcribed in mature asexual blood stages by individual parasites, that VIR proteins are not clonally expressed and that there is no significant difference in the recognition of VIR-tags by immune sera of first-infected patients compared with sera of multiple-infected patients. These data provide to our knowledge the first comprehensive study of vir genes and their encoding variant proteins in natural infections and thus constitute a baseline for future studies of this multigene superfamily. Moreover, whereas our data are consistent with a major role of vir genes in natural infections, they are inconsistent with a predominant role in the strict sense of antigenic variation.
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Affiliation(s)
- Carmen Fernandez-Becerra
- Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, Avenida Lineu Prestes 1374, São Paulo, SP 05508-900, Brazil
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63
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Abstract
Women become more susceptible to Plasmodium falciparum malaria during pregnancy, and the risk of disease and death is high for both the mother and her fetus. In low transmission areas, women of all parities are at risk for severe syndromes like cerebral malaria, and maternal and fetal mortality are high. In high transmission areas, where women are most susceptible during their first pregnancies, severe syndromes like cerebral malaria are uncommon, but severe maternal anemia and low birth weight are frequent sequelae and account for an enormous loss of life. P. falciparum-infected red cells sequester in the intervillous space of the placenta, where they adhere to chondroitin sulfate A but not to receptors like CD36 that commonly support adhesion of parasites infecting nonpregnant hosts. Poor pregnancy outcomes due to malaria are related to the macrophage-rich infiltrates and pro-inflammatory cytokines such as tumor necrosis factor-alpha that accumulate in the intervillous space. Women who acquire antibodies against chrondroitin sulfate A (CSA)-binding parasites are less likely to have placental malaria, and are more likely to deliver healthy babies. In areas of stable transmission, women acquire antibodies against CSA-binding parasites over successive pregnancies, explaining the high susceptibility to malaria during first pregnancy, and suggesting that a vaccine to prevent pregnancy malaria should target placental parasites. Prevention and treatment of malaria are essential components of antenatal care in endemic areas, but require special considerations during pregnancy. Recrudescence after drug treatment is more common during pregnancy, and the spread of drug-resistant parasites has eroded the usefulness of the few drugs known to be safe for the woman and her fetus. Determining the safety and effectiveness of newer antimalarials in pregnant women is an urgent priority. A vaccine that prevents pregnancy malaria due to P. falciparum could be delivered before first pregnancy, and would have an enormous impact on mother-child health in tropical areas.
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Affiliation(s)
- P E Duffy
- Seattle Biomedical Research Institute, 307 Westlake Avenue, Seattle, WA, USA.
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64
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Russell C, Mercereau-Puijalon O, Le Scanf C, Steward M, Arnot DE. Further definition of PfEMP-1 DBL-1alpha domains mediating rosetting adhesion of Plasmodium falciparum. Mol Biochem Parasitol 2005; 144:109-13. [PMID: 16122820 DOI: 10.1016/j.molbiopara.2005.06.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2005] [Revised: 06/22/2005] [Accepted: 06/29/2005] [Indexed: 11/25/2022]
Affiliation(s)
- Clare Russell
- Institute of Immunology and Infection Research, Division of Biological Sciences, Ashworth Laboratory, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK
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65
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Bull PC, Berriman M, Kyes S, Quail MA, Hall N, Kortok MM, Marsh K, Newbold CI. Plasmodium falciparum variant surface antigen expression patterns during malaria. PLoS Pathog 2005; 1:e26. [PMID: 16304608 PMCID: PMC1287908 DOI: 10.1371/journal.ppat.0010026] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2005] [Accepted: 10/11/2005] [Indexed: 11/23/2022] Open
Abstract
The variant surface antigens expressed on Plasmodium falciparum–infected erythrocytes are potentially important targets of immunity to malaria and are encoded, at least in part, by a family of var genes, about 60 of which are present within every parasite genome. Here we use semi-conserved regions within short var gene sequence “tags” to make direct comparisons of var gene expression in 12 clinical parasite isolates from Kenyan children. A total of 1,746 var clones were sequenced from genomic and cDNA and assigned to one of six sequence groups using specific sequence features. The results show the following. (1) The relative numbers of genomic clones falling in each of the sequence groups was similar between parasite isolates and corresponded well with the numbers of genes found in the genome of a single, fully sequenced parasite isolate. In contrast, the relative numbers of cDNA clones falling in each group varied considerably between isolates. (2) Expression of sequences belonging to a relatively conserved group was negatively associated with the repertoire of variant surface antigen antibodies carried by the infected child at the time of disease, whereas expression of sequences belonging to another group was associated with the parasite “rosetting” phenotype, a well established virulence determinant. Our results suggest that information on the state of the host–parasite relationship in vivo can be provided by measurements of the differential expression of different var groups, and need only be defined by short stretches of sequence data. Hope that it will be possible to develop a malaria vaccine is supported by the fact that individuals who have grown up in malaria endemic regions learn to carry malarial infections without suffering disease. Surprisingly little is still known about how this immunity develops. Much current research focuses on how the host develops immune responses to parasite antigens that are exposed to the host immune system. A major family of such antigens are inserted into the surface of parasite-infected erythrocytes, where they undergo antigenic switching to evade a developing antibody response. These proteins are encoded by a family of approximately 60 var genes, variants of which are present in every parasite genome. The extreme diversity of the var genes has prevented meaningful comparison of their expression in clinical isolates. However, the authors of this paper show that var genes can be placed in groups that have a similar representation in the genomes of all parasites that the authors collected from Kenyan children. Having demonstrated an underlying similarity at the genomic level, the authors show that the var expression patterns vary markedly between different patients. The expression levels of specific groups of var genes was associated with poorly developed antibody responses in the children and a well-established parasite virulence phenotype. The study provides tools for exploring how host and parasite adapt to one another as immunity develops.
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Affiliation(s)
- Peter C Bull
- Nuffield Department of Clinical Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom.
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66
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Ralph SA, Bischoff E, Mattei D, Sismeiro O, Dillies MA, Guigon G, Coppee JY, David PH, Scherf A. Transcriptome analysis of antigenic variation in Plasmodium falciparum--var silencing is not dependent on antisense RNA. Genome Biol 2005; 6:R93. [PMID: 16277748 PMCID: PMC1297649 DOI: 10.1186/gb-2005-6-11-r93] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2005] [Revised: 07/12/2005] [Accepted: 09/21/2005] [Indexed: 11/10/2022] Open
Abstract
A microarray analysis of Plasmodium falciparum selected to express different var genes suggests that antisense transcripts are not responsible for the transcriptional silencing of non-expressed var genes. Background Plasmodium falciparum, the causative agent of the most severe form of malaria, undergoes antigenic variation through successive presentation of a family of antigens on the surface of parasitized erythrocytes. These antigens, known as Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) proteins, are subject to a mutually exclusive expression system, and are encoded by the multigene var family. The mechanism whereby inactive var genes are silenced is poorly understood. To investigate transcriptional features of this mechanism, we conducted a microarray analysis of parasites that were selected to express different var genes by adhesion to chondroitin sulfate A (CSA) or CD36. Results In addition to oligonucleotides for all predicted protein-coding genes, oligonucleotide probes specific to each known var gene of the FCR3 background were designed and added to the microarray, as well as tiled sense and antisense probes for a subset of var genes. In parasites selected for adhesion to CSA, one full-length var gene (var2csa) was strongly upregulated, as were sense RNA molecules emanating from the 3' end of a limited subset of other var genes. No global relationship between sense and antisense production of var genes was observed, but notably, some var genes had coincident high levels of both antisense and sense transcript. Conclusion Mutually exclusive expression of PfEMP1 proteins results from transcriptional silencing of non-expressed var genes. The distribution of steady-state sense and antisense RNA at var loci are not consistent with a silencing mechanism based on antisense silencing of inactive var genes. Silencing of var loci is also associated with altered regulation of genes distal to var loci.
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Affiliation(s)
- Stuart A Ralph
- Institut Pasteur, Unit of Biology of Host-Parasite Interactions, Centre National de la Recherche Scientifique, Unité de Recherche Associée 2581, 25 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne 3050, Victoria, Australia
| | - Emmanuel Bischoff
- Institut Pasteur, Plate-Forme 2 - Puces à ADN, 28 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
| | - Denise Mattei
- Institut Pasteur, Unit of Biology of Host-Parasite Interactions, Centre National de la Recherche Scientifique, Unité de Recherche Associée 2581, 25 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
| | - Odile Sismeiro
- Institut Pasteur, Plate-Forme 2 - Puces à ADN, 28 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
| | - Marie-Agnès Dillies
- Institut Pasteur, Plate-Forme 2 - Puces à ADN, 28 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
| | - Ghislaine Guigon
- Institut Pasteur, Plate-Forme 2 - Puces à ADN, 28 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
- Institut Pasteur, Plate-Forme 8 - CNR/Santé Publique, 28 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
| | - Jean-Yves Coppee
- Institut Pasteur, Plate-Forme 2 - Puces à ADN, 28 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
| | - Peter H David
- Institut Pasteur, Unité d'Immunologie Moléculaire des Parasites, 28 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
| | - Artur Scherf
- Institut Pasteur, Unit of Biology of Host-Parasite Interactions, Centre National de la Recherche Scientifique, Unité de Recherche Associée 2581, 25 Rue du Docteur Roux, F-75724 Paris Cedex 15, France
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67
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Ralph SA, Scherf A. The epigenetic control of antigenic variation in Plasmodium falciparum. Curr Opin Microbiol 2005; 8:434-40. [PMID: 15979386 DOI: 10.1016/j.mib.2005.06.007] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Accepted: 06/14/2005] [Indexed: 11/16/2022]
Abstract
Much of what is known about antigenic variation in the human malaria parasite Plasmodium falciparum has been established by the study of phenotypic changes at the surface of parasitized red blood cells. Although this has contributed to our fundamental understanding of immune escape, nothing conclusive has been elucidated about the molecular mechanisms that determine activation and silencing of members of the antigenic variation var gene family. Recent findings indicate that reversible chromatin modifications and perinuclear gene movement are epigenetic factors that define the silent and active states of telomere-adjacent var genes.
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Affiliation(s)
- Stuart A Ralph
- Institut Pasteur, Biology of Host-Parasite Interactions, URA 2581, 25 Rue du Docteur Roux, Paris, 75015, France.
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68
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Gannoun-Zaki L, Jost A, Mu J, Deitsch KW, Wellems TE. A silenced Plasmodium falciparum var promoter can be activated in vivo through spontaneous deletion of a silencing element in the intron. EUKARYOTIC CELL 2005; 4:490-2. [PMID: 15701812 PMCID: PMC549332 DOI: 10.1128/ec.4.2.490-492.2005] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Introns of Plasmodium falciparum var genes act as transcriptional silencing elements that help control antigenic variations. In transfected episomes, intron silencing of a drug-selectable marker under var promoter control is reversed by the spontaneous deletion of key intron regions. The resulting promoter activation does not affect the transcription of chromosomal var genes.
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Affiliation(s)
- Laïla Gannoun-Zaki
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-8132, USA
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69
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Cunningham DA, Jarra W, Koernig S, Fonager J, Fernandez-Reyes D, Blythe JE, Waller C, Preiser PR, Langhorne J. Host immunity modulates transcriptional changes in a multigene family (yir) of rodent malaria. Mol Microbiol 2005; 58:636-47. [PMID: 16238615 DOI: 10.1111/j.1365-2958.2005.04840.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Variant antigens, encoded by multigene families, and expressed at the surface of erythrocytes infected with the human malaria parasite Plasmodium falciparum and the simian parasite Plasmodium knowlesi, are important in evasion of host immunity. The vir multigene family, encoding a very large number of variant antigens, has been identified in the human parasite Plasmodium vivax and homologues (yir) of this family exist in the rodent parasite Plasmodium yoelii. These genes are part of a superfamily (pir) which are found in Plasmodium species infecting rodents, monkeys and humans (P. yoelii, P. berghei, P. chabaudi, P. knowlesi and P. vivax). Here, we show that YIR proteins are expressed on the surface of erythrocytes infected with late-stage asexual parasites, and that host immunity modulates transcription of yir genes. The surface location and expression pattern of YIR is consistent with a role in antigenic variation. This provides a unique opportunity to study the regulation and expression of the pir superfamily, and its role in both protective immunity and antigenic variation, in an easily accessible animal model system.
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Affiliation(s)
- Deirdre A Cunningham
- Division of Parasitology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK
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70
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Abstract
The erythrocytic cycle of Plasmodium falciparum presents a particularity in relation to other Plasmodium species that infect man. Mature trophozoites and schizonts are sequestered from the peripheral circulation due to adhesion of infected erythrocytes to host endothelial cells. Modifications in the surface of infected erythrocytes, termed knobs, seem to facilitate adhesion to endothelium and other erythrocytes. Adhesion provides better maturation in the microaerophilic venous atmosphere and allows the parasite to escape clearance by the spleen which recognizes the erythrocytes loss of deformability. Adhesion to the endothelium, or cytoadherence, has an important role in the pathogenicity of the disease, causing occlusion of small vessels and contributing to failure of many organs. Cytoadherence can also describe adhesion of infected erythrocytes to uninfected erythrocytes, a phenomenon widely known as rosetting. Clinical aspects of severe malaria, as well as the host receptors and parasite ligands involved in cytoadherence and rosetting, are reviewed here. The erythrocyte membrane protein 1 of P. falciparum (PfEMP1) appears to be the principal adhesive ligand of infected erythrocytes and will be discussed in more detail. Understanding the role of host receptors and parasite ligands in the development of different clinical syndromes is urgently needed to identify vaccination targets in order to decrease the mortality rates of this disease.
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Affiliation(s)
- Karin Kirchgatter
- Núcleo de Estudos em Malária, Superintendência de Controle de Endemias (SUCEN), Instituto de Medicina Tropical de São Paulo (IMTSP), Universidade de São Paulo (USP), São Paulo, SP 05403-000, Brazil.
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71
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Duffy MF, Byrne TJ, Elliott SR, Wilson DW, Rogerson SJ, Beeson JG, Noviyanti R, Brown GV. Broad analysis reveals a consistent pattern of var gene transcription in Plasmodium falciparum repeatedly selected for a defined adhesion phenotype. Mol Microbiol 2005; 56:774-88. [PMID: 15819631 DOI: 10.1111/j.1365-2958.2005.04577.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Transcription of the majority of the members of the Plasmodium falciparum var multigene family were analysed in two isolates by a quantitative approach. Both of these isolates had been repeatedly selected for adhesion to chondroitin sulphate A (CSA) and one had also been selected for adhesion to hyaluronic acid (HA). These adhesion phenotypes are expressed by many parasites isolated from placentae and are associated with malaria disease in pregnancy. Increased transcription of the var gene var2csa, or its homologue IT4 var4, was associated with the CSA and HA adhesion phenotypes in all parasites suggesting that it was the dominant, if not the only, var gene that encoded adhesion to CSA in these allogeneic isolates. Some var genes were consistently transcribed at higher levels than others regardless of expressed adhesion phenotypes suggesting a transcriptional hierarchy. Unspliced or partial transcripts were detected for most var genes tested. These atypical var gene transcripts may have implications for the regulation of var gene transcription.
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Affiliation(s)
- Michael F Duffy
- Department of Medicine, University of Melbourne, Royal Melbourne Hospital, Parkville, Victoria, Australia.
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72
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Wunderlich G, Alves FP, Gölnitz U, Tada MS, Camargo EFPD, Pereira-da-Silva LH. Rapid turnover of Plasmodium falciparum var gene transcripts and genotypes during natural non-symptomatic infections. Rev Inst Med Trop Sao Paulo 2005; 47:195-201. [PMID: 16138199 DOI: 10.1590/s0036-46652005000400004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The var genes of Plasmodium falciparum code for the antigenically variant erythrocyte membrane proteins 1 (PfEMP1), a major factor for cytoadherence and immune escape of the parasite. Herein, we analyzed the var gene transcript turnover in two ongoing, non-symptomatic infections at sequential time points during two weeks. The number of different circulating genomes was estimated by microsatellite analyses. In both infections, we observed a rapid turnover of plasmodial genotypes and var transcripts. The rapidly changing repertoire of var transcripts could have been caused either by swift elimination of circulating var-transcribing parasites stemming from different or identical genetic backgrounds, or by accelerated switching of var gene transcription itself.
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Affiliation(s)
- Gerhard Wunderlich
- Departamento de Parasitologia, Instituto de Ciências Biomédicas 2, Universidade de São Paulo, 05508-900 São Paulo, SP, Brazil.
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73
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Dodin G, Levoir P. Replication slippage and the dynamics of the immune response in malaria: a formal model for immunity. Parasitology 2005; 131:727-35. [PMID: 16336726 DOI: 10.1017/s0031182005008462] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2005] [Revised: 04/21/2005] [Accepted: 06/01/2005] [Indexed: 11/06/2022]
Abstract
A simple mathematical model of the dynamics of malaria invasion is proposed. The model is based on the hypothesis that replication slippage (slipped strand mispairing occurring in replicating DNAs), likely to take place within regular, low-complexity, regions of the plasmodium genome, is a significant mechanism of the ability for the parasite to escape the host immune defence. The model reconciles the conclusions of other formal approaches like periodic bursts of parasitaemia and, in particular, it predicts that antibody cross-reactivity affects the level and the time profile of malaria recrudescence. It also suggests that an efficient strategy for the parasite to escape host humoral immune defences is to express a single antigen. Linking local complexity to antigenic variability tentatively allows prediction of new potentially immunogenic sequences in the plasmodium genome.
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Affiliation(s)
- G Dodin
- Université Denis Diderot, ITODYS, 1 Rue Guy de la Brosse, 75005 Paris, France.
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74
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Elliott SR, Duffy MF, Byrne TJ, Beeson JG, Mann EJ, Wilson DW, Rogerson SJ, Brown GV. Cross-reactive surface epitopes on chondroitin sulfate A-adherent Plasmodium falciparum-infected erythrocytes are associated with transcription of var2csa. Infect Immun 2005; 73:2848-56. [PMID: 15845490 PMCID: PMC1087379 DOI: 10.1128/iai.73.5.2848-2856.2005] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Malaria in pregnancy is associated with placental accumulation of Plasmodium falciparum-infected erythrocytes (IE) that adhere to chondroitin sulfate A (CSA). Adhesion is mediated by P. falciparum erythrocyte membrane protein 1 (PfEMP1), a variant parasite protein expressed on the surface of IE and encoded by var genes. Rabbit antiserum was generated against the CSA-adherent P. falciparum line CS2, in which the dominant var transcribed is var2csa, a relatively conserved var gene that has been associated with CSA adhesion. Anti-CS2 recognized genetically distinct CSA-adherent P. falciparum lines but not CD36-adherent parent lines. Reactivity with anti-CS2 correlated with the level of adhesion to CSA. Fluorescence-activated cell sorting according to binding of anti-CS2 showed reactivity was associated with CSA adhesion and transcription of var2csa. These data are consistent with the hypothesis that var2csa encodes a PfEMP1 expressed on the surface of IE, which mediates adhesion to CSA and is relatively conserved between genetically distinct strains of P. falciparum.
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Affiliation(s)
- Salenna R Elliott
- Department of Medicine, University of Melbourne, Royal Melbourne Hospital, Victoria 3050 Australia.
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75
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Lavstsen T, Magistrado P, Hermsen CC, Salanti A, Jensen ATR, Sauerwein R, Hviid L, Theander TG, Staalsoe T. Expression of Plasmodium falciparum erythrocyte membrane protein 1 in experimentally infected humans. Malar J 2005; 4:21. [PMID: 15857512 PMCID: PMC1112614 DOI: 10.1186/1475-2875-4-21] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2005] [Accepted: 04/27/2005] [Indexed: 11/10/2022] Open
Abstract
Background Parasites causing severe malaria in non-immune patients express a restricted subset of variant surface antigens (VSA), which are better recognized by immune sera than VSA expressed during non-severe disease in semi-immune individuals. The most prominent VSA are the var gene-encoded Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family, which is expressed on the surface of infected erythrocytes where it mediates binding to endothelial receptors. Thus, severe malaria may be caused by parasites expressing PfEMP1 variants that afford parasites optimal sequestration in immunologically naïve individuals and high effective multiplication rates. Methods var gene transcription was analysed using real time PCR and PfEMP1 expression by western blots as well as immune plasma recognition of parasite cultures established from non-immune volunteers shortly after infection with NF54 sporozoites. Results In cultures representing the first generation of parasites after hepatic release, all var genes were transcribed, but GroupA var genes were transcribed at the lowest levels. In cultures established from second or third generation blood stage parasites of volunteers with high in vivo parasite multiplication rates, the var gene transcription pattern differed markedly from the transcription pattern of the cultures representing first generation parasites. This indicated that parasites expressing specific var genes, mainly belonging to group A and B, had expanded more effectively in vivo compared to parasites expressing other var genes. The differential expression of PfEMP1 was confirmed at the protein level by immunoblot analysis. In addition, serological typing showed that immune sera more often recognized second and third generation parasites than first generation parasites. Conclusion In conclusion, the results presented here support the hypothesis that parasites causing severe malaria express a subset of PfEMP1, which bestows high parasite growth rates in individuals with limited pre-existing immunity.
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Affiliation(s)
- Thomas Lavstsen
- Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Panum Institute 24-2, Blegdamsvej 3, 2200 Copenhagen N, Denmark
| | - Pamela Magistrado
- Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Panum Institute 24-2, Blegdamsvej 3, 2200 Copenhagen N, Denmark
| | | | - Ali Salanti
- Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Panum Institute 24-2, Blegdamsvej 3, 2200 Copenhagen N, Denmark
| | - Anja TR Jensen
- Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Panum Institute 24-2, Blegdamsvej 3, 2200 Copenhagen N, Denmark
| | - Robert Sauerwein
- Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
| | - Lars Hviid
- Centre for Medical Parasitology at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
| | - Thor G Theander
- Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Panum Institute 24-2, Blegdamsvej 3, 2200 Copenhagen N, Denmark
| | - Trine Staalsoe
- Centre for Medical Parasitology at Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
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76
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Springer AL, Smith LM, Mackay DQ, Nelson SO, Smith JD. Functional interdependence of the DBLbeta domain and c2 region for binding of the Plasmodium falciparum variant antigen to ICAM-1. Mol Biochem Parasitol 2005; 137:55-64. [PMID: 15279951 DOI: 10.1016/j.molbiopara.2004.03.019] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2003] [Revised: 12/12/2003] [Accepted: 03/28/2004] [Indexed: 11/18/2022]
Abstract
Cytoadherence of Plasmodium falciparum-infected erythrocytes is associated with severe malaria and is primarily mediated through binding of the variant surface antigen P. falciparum erythrocyte membrane protein 1 (PfEMP1) to specific host ligands. Infected erythrocyte binding to Intercellular Adhesion Molecule 1 (ICAM-1) has been implicated as having a role in cerebral malaria, a major cause of death from P. falciparum infection. We have examined ICAM-1-binding PfEMP1 proteins in the cytoadhesive P. falciparum strain IT4/25/5 in order to extend our understanding of binding. For A4tres, the ICAM-1 binding region was previously shown to reside within contiguous DBL2beta and c2 domains. We determined the gene sequence encoding IT-ICAM var, and showed that ICAM-1 binding in this protein also maps to DBL2betac2 domains that have 48% amino acid identity to A4tres. By truncation and chimera analysis, most of the DBL2beta and the first half of the c2 region were required for A4tres binding to ICAM-1, suggesting this tandem should be considered a structural-functional combination for ICAM-1 binding. Of interest, a chimera formed between two different ICAM-1 binding domains did not bind ICAM-1, suggesting a functional interdependence between DBL2beta and c2 from the same protein. As gene recombination and gene conversion are important mechanisms for generating diversity in the PfEMP1 protein family, this finding implies an extra level of constraint on the functional evolution of binding traits. Knowledge about the PfEMP1::ICAM-1 interaction may allow the development of interventions to prevent binding and disease.
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Affiliation(s)
- Amy L Springer
- Seattle Biomedical Research Institute, 307 Westlake Avenue N, Suite 500, WA 98109-5219, USA
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Corredor V, Meyer EVS, Lapp S, Corredor-Medina C, Huber CS, Evans AG, Barnwell JW, Galinski MR. A SICAvar switching event in Plasmodium knowlesi is associated with the DNA rearrangement of conserved 3′ non-coding sequences. Mol Biochem Parasitol 2004; 138:37-49. [PMID: 15500914 DOI: 10.1016/j.molbiopara.2004.05.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2003] [Revised: 04/23/2004] [Accepted: 05/09/2004] [Indexed: 10/26/2022]
Abstract
Plasmodium knowlesi variant antigens are expressed at the surface of infected erythrocytes and are encoded by the Schizont Infected Cell Agglutination variant antigen (SICAvar) multigene family. The 3' region of the SICAvar gene locus encoding the 205 kDa variant antigen expressed in the Pk1(B+)1+ parasites was found to be altered compared to the Pk1(A+) parental clone. Here we report that this alteration is the result of a DNA rearrangement and that the original and altered 205 SICAvar alleles appear to encode bona fide variant antigens. Importantly, 205A and 205B SICAvar RNA sequences are detectable in similar apparent quantities as determined by quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) amplification experiments. However, expression of the 205 kDa SICA protein at the surface of the infected erythrocyte is not characteristic of the Pk1(A+) parasites and the 205 SICAvar transcript has not been detected in Pk1(A+) parasites by northern blot analysis. Furthermore, we report that many distinct SICAvar transcripts were detected in P. knowlesi Pk1(B+)1+ cDNA library hybridization screens. Of special interest, in light of these data, distinctive differences at the 3' end of the 205A and 205B alleles are observed, which may be of functional importance. An analysis of the 3' untranslated region (UTR) of SICAvar genes in more than 100 sequences revealed a surprising common sequence pattern characterized by blocks of imperfect, GT-rich, heptad repeated motifs (Block I), followed by A and T rich homopolymers (Block II) and in a large number of genes, GC-rich segments (Block III). We show that this region undergoes extensive recombination and that the preferential stability of the 205 SICAvar transcript in Pk1(B+)1+ parasites may be associated with the presence of its specific Block III sequences. We speculate that the conserved yet polymorphic SICAvar 3'UTR sequences, and comparable regions in P. falciparum var genes, function in the stage-specific and developmentally regulated post-transcriptional gene silencing (PTGS) of variant antigen transcripts.
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Affiliation(s)
- Vladimir Corredor
- Emory Vaccine Center, Yerkes National Primate Research Center, Emory University, 954 Gatewood Road, Atlanta, GA 30329, USA
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78
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Abstract
Sequestration of Plasmodium falciparum-infected erythrocytes in the placenta is responsible for many of the harmful effects of malaria during pregnancy. Sequestration occurs as a result of parasite adhesion molecules expressed on the surface of infected erythrocytes binding to host receptors in the placenta such as chondroitin sulphate A (CSA). Identification of the parasite ligand(s) responsible for placental adhesion could lead to the development of a vaccine to induce antibodies to prevent placental sequestration. Such a vaccine would reduce the maternal anaemia and infant deaths that are associated with malaria in pregnancy. Current research indicates that the parasite ligands mediating placental adhesion may be members of the P. falciparum variant surface antigen family PfEMP1, encoded by var genes. Two relatively well-conserved subfamilies of var genes have been implicated in placental adhesion, however, their role remains controversial. This review examines the evidence for and against the involvement of var genes in placental adhesion, and considers whether the most appropriate vaccine candidates have yet been identified.
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Affiliation(s)
- J A Rowe
- Institute of Cell, Animal and Population Biology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, UK.
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79
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Horrocks P, Pinches R, Christodoulou Z, Kyes SA, Newbold CI. Variable var transition rates underlie antigenic variation in malaria. Proc Natl Acad Sci U S A 2004; 101:11129-34. [PMID: 15256597 PMCID: PMC503751 DOI: 10.1073/pnas.0402347101] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2004] [Indexed: 11/18/2022] Open
Abstract
Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is expressed on the surface of infected erythrocytes where it plays a central role in both infected erythrocytes cytoadhesion and immune evasion. Switches in clonal expression of PfEMP1 result in antigenic variation that facilitates long-term chronic infection of the host. The var gene family encodes PfEMP1 variants, with transcriptional switching between different var variants providing the molecular basis for antigenic variation. Despite the importance of var transcriptional switching in the evasion of the immune response, little is known about the way in which this process is regulated. Here we report the measurement of transition on and off rates for a series of var gene variants. We find (i) that on and off rates for a given variant are dissimilar, (ii) that these rates vary dramatically among different variants, and (iii) that in isogenic clones expressing the same var gene, both on and off rates are constant and appear to be an intrinsic property of that particular gene. These data would suggest that the information that determines the probability of the activation or silencing of var genes is present in their surrounding DNA. Furthermore, some transitions appear to be disallowed depending on the recent variant antigen expression history of the parasite clone. These findings have important implications for both the underlying molecular mechanisms of antigenic variation and the processes that promote chronicity of infection in vivo.
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Affiliation(s)
- Paul Horrocks
- Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.
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80
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Kraemer SM, Smith JD. Evidence for the importance of genetic structuring to the structural and functional specialization of the Plasmodium falciparum var gene family. Mol Microbiol 2004; 50:1527-38. [PMID: 14651636 DOI: 10.1046/j.1365-2958.2003.03814.x] [Citation(s) in RCA: 177] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The var gene family encodes Plasmodium falciparum erythrocyte membrane 1 (PfEMP1) proteins that act as virulence factors responsible for both antigenic variation and cytoadherence of infected erythrocytes. These proteins orchestrate infected erythrocyte sequestration from blood circulation and contribute to adhesion-based complications of P. falciparum malaria infections. For this study, we analysed the genetic organization and strain structure of var genes and present evidence for three separately evolving groups that have, in part, functionally diverged and differ between subtelomeric and central chromosomal locations. Our analyses suggest that a recombination hierarchy limits reassortment between groups and may explain why some var genes are unusually conserved between parasite strains. This recombination hierarchy, coupled with binding and immune selection, shapes the variant antigen repertoire and has structural, functional and evolutionary consequences for the PfEMP1 protein family that are directly relevant to malaria pathogenesis.
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Affiliation(s)
- Susan M Kraemer
- Seattle Biomedical Research Institute, 4 Nickerson Street, Seattle, WA 98109, USA
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81
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Abstract
Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is an important virulence factor encoded by a family of roughly 60 var genes and is used by the parasite to interact with the human host. The parasite regularly exchanges the expressed var gene generating antigenic variation of the infected RBCs (pRBC) surface which is crucial for successful proliferation and transmission. PfEMP1 is also an adhesive molecule that binds to an array of human receptors. By sequestration in the post-capillary venules, pRBCs are able to escape the spleen-mediated clearance but severe malaria may develop if the local binding is extensive. Anti-PfEMP1 immunity is important for preventing the development of both cerebral malaria and placental malaria, but more immunological studies on PfEMP1 antigens and their interaction with the human host are needed. Over the last few years our knowledge about var genes and PfEMP1s has increased dramatically through genetic, biochemical, immunological and epidemiological studies. In addition, the genome sequence has also provided us with a new platform for further dissecting its biological functions. This review highlights the recent analyses of var genes in the P. falciparum genome and postulates significance of genome recombination to the diversity of parasite virulence.
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Affiliation(s)
- Kirsten Flick
- Microbiology and Tumour Biology Centre (MTC), Karolinska Institutet and Swedish Institute for Infectious Disease Control, Box 280, SE-171 77 Stockholm, Sweden
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82
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Galinski MR, Corredor V. Variant antigen expression in malaria infections: posttranscriptional gene silencing, virulence and severe pathology. Mol Biochem Parasitol 2004; 134:17-25. [PMID: 14747139 DOI: 10.1016/j.molbiopara.2003.09.013] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Mary R Galinski
- Emory Vaccine Center, Yerkes National Primate Research Center, Emory University, 954 Gatewood Road, Atlanta, GA 30329, USA.
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83
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Chattopadhyay R, Taneja T, Chakrabarti K, Pillai CR, Chitnis CE. Molecular analysis of the cytoadherence phenotype of a Plasmodium falciparum field isolate that binds intercellular adhesion molecule—1. Mol Biochem Parasitol 2004; 133:255-65. [PMID: 14698437 DOI: 10.1016/j.molbiopara.2003.08.014] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The ability of Plasmodium falciparum-infected erythrocytes to adhere to endothelial receptors and sequester in diverse host organs is an important pathogenic mechanism. Cytoadherence is mediated by variant surface antigens, which are referred to as PfEMP-1 and are encoded by var genes. The extracellular regions of PfEMP-1 contain multiple conserved cysteine-rich domains that are referred to as Duffy-binding-like (DBL) domains. Here, we analyze the adhesive phenotype of an Indian P. falciparum field isolate, JDP8, which binds ICAM-1 but does not bind CD36. This is a unique cytoadherence phenotype because P. falciparum strains that bind ICAM-1 described thus far usually also bind CD36. Moreover, binding to both receptors is thought to be important for static adhesion under flow. The ICAM-1 binding population of P. falciparum JDP8 adheres to endothelial cells under flow despite poor binding to CD36. We have also identified an expressed var gene, JDP8Icvar, which mediates the ICAM-1 binding phenotype of JDP8. Expression of different regions of JDP8Icvar on the surface of COS-7 cells followed by binding assays demonstrates that the ICAM-1 binding domain maps to the DBL2betaC2 domain of JDP8Icvar. Sequence comparison with two previously identified ICAM-1 binding domains of PfEMP-1, which also map to DBLbetaC2 domains, suggests that diverse P. falciparum isolates use a structurally conserved domain to bind ICAM-1. It thus appears that functional constraints may place limits on the extent of sequence diversity in receptor-binding domains of PfEMP-1.
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Affiliation(s)
- Rana Chattopadhyay
- Malaria Research Group, International Centre for Genetic Engineering and Biotechnology (ICGEB), Aruna Asaf Ali Marg, New Delhi 110067, India
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84
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Noviyanti R, Brown GV. Phenotypic switching and var gene transcription in Plasmodium falciparum. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 531:149-59. [PMID: 12916787 DOI: 10.1007/978-1-4615-0059-9_11] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/04/2023]
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85
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Lavstsen T, Salanti A, Jensen ATR, Arnot DE, Theander TG. Sub-grouping of Plasmodium falciparum 3D7 var genes based on sequence analysis of coding and non-coding regions. Malar J 2003; 2:27. [PMID: 14565852 PMCID: PMC222925 DOI: 10.1186/1475-2875-2-27] [Citation(s) in RCA: 257] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2003] [Accepted: 09/10/2003] [Indexed: 11/10/2022] Open
Abstract
Background The variant surface antigen family Plasmodium falciparum erythrocyte membrane protein-1 (PfEMP1) is an important target for protective immunity and is implicated in the pathology of malaria through its ability to adhere to host endothelial receptors. The sequence diversity and organization of the 3D7 PfEMP1 repertoire was investigated on the basis of the complete genome sequence. Methods Using two tree-building methods we analysed the coding and non-coding sequences of 3D7 var and rif genes as well as var genes of other parasite strains. Results var genes can be sub-grouped into three major groups (group A, B and C) and two intermediate groups B/A and B/C representing transitions between the three major groups. The best defined var group, group A, comprises telomeric genes transcribed towards the telomere encoding PfEMP1s with complex domain structures different from the 4-domain type dominant of groups B and C. Two sequences belonging to the var1 and var2 subfamilies formed independent groups. A rif subgroup transcribed towards the centromere was found neighbouring var genes of group A such that the rif and var 5' regions merged. This organization appeared to be unique for the group A var genes Conclusion The grouping of var genes implies that var gene recombination preferentially occurs within var gene groups and it is speculated that the groups reflect a functional diversification evolved to cope with the varying conditions of transmission and host immune response met by the parasite.
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Affiliation(s)
- Thomas Lavstsen
- Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Denmark
| | - Ali Salanti
- Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Denmark
| | - Anja TR Jensen
- Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Denmark
| | - David E Arnot
- Institute for Cell, Animal, and Population Biology, University of Edinburgh, Scotland, United Kingdom
| | - Thor G Theander
- Centre for Medical Parasitology at Institute for Medical Microbiology and Immunology, University of Copenhagen, Denmark
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86
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Calderwood MS, Gannoun-Zaki L, Wellems TE, Deitsch KW. Plasmodium falciparum var genes are regulated by two regions with separate promoters, one upstream of the coding region and a second within the intron. J Biol Chem 2003; 278:34125-32. [PMID: 12832422 DOI: 10.1074/jbc.m213065200] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Antigenic variation in Plasmodium falciparum malaria parasites results from switches in expression among members of the multicopy var gene family. This family is subject to allelic exclusion by which particular genes are expressed while the rest of the family remains transcriptionally silent. Evidence from reporter constructs indicates that var gene silencing involves a cooperative interaction between the var intron and an upstream element and requires transition of the parasites through S-phase of the cell cycle. These findings implicate chromatin assembly in the process of regulating var gene expression and antigenic variation. Here we characterize the var intron and the elements within it that are necessary for var transcriptional silencing. Alignments of var introns show a highly conserved structure that consists of three discreet regions with distinct base pair compositions. The middle region is highly AT-rich and is sufficient to silence an associated var promoter. Constructs that include a typical var intron upstream of a reporter gene or drug-selectable marker reveal that the intron also possesses promoter activity, presumably providing an explanation for the origin of the previously described var "sterile" transcripts. Deletions that disable the promoter activity of the intron also eliminate its ability to function as a silencer. These findings suggest that interactions between the regions of these two promoters and the generation of the sterile transcripts play a significant role in regulating var gene expression.
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Affiliation(s)
- Michael S Calderwood
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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87
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Andrews KT, Pirrit LA, Przyborski JM, Sanchez CP, Sterkers Y, Ricken S, Wickert H, Lépolard C, Avril M, Scherf A, Gysin J, Lanzer M. Recovery of adhesion to chondroitin-4-sulphate in Plasmodium falciparum varCSA disruption mutants by antigenically similar PfEMP1 variants. Mol Microbiol 2003; 49:655-69. [PMID: 12864850 DOI: 10.1046/j.1365-2958.2003.03595.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Protection against maternal malaria has been associated with the acquisition of a specific antibody response that prevents adhesion of Plasmodium falciparum-infected erythrocytes to the glycosaminoglycan chondroitin-4-sulphate (CSA), which is present in the placental intervillous space. These antibodies are directed against variant forms of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) that mediate binding to CSA. We have generated insertional disruption mutants of the gene encoding the CSA-binding phenotype in the P. falciparum clone FCR3 (varCSA) to test the hypothesis that strategies targeting the parasite's determinant for this adhesive phenotype may prevent sequestration of infected erythrocytes in the placenta and hence the development of maternal malaria. The varCSA-disruption mutants were initially unable to adhere to CSA; however, they could recover the phenotype after repeated selection over CSA. We show that recovery of CSA binding is varCSA independent and mediated by the activation of a novel var variant. Importantly, the corresponding PfEMP1 protein reacts with a monoclonal antibody recognizing the DBL3 gamma domain of the varCSA gene product, indicating that the DBL3 gamma CSA-binding domains are conserved between these PfEMP1-binding variants. Our data support strategies exploring these conserved epitopes as vaccine candidates against maternal malaria.
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88
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Sodeinde O, Clarke JL, Vulliamy TJ, Luzzatto L, Mason PJ. Expression of Plasmodium falciparum G6PD-6PGL in laboratory parasites and in patient isolates in G6PD-deficient and normal Nigerian children. Br J Haematol 2003; 122:662-8. [PMID: 12899722 DOI: 10.1046/j.1365-2141.2003.04397.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
As the production of NADPH in the pentose phosphate pathway is the main antioxidant defence mechanism available to the Plasmodium falciparum, we have studied the expression of P. falciparum glucose 6-phosphate dehydrogenase-6-phosphogluconolactonase (PfG6PD-6PGL) in G6PD-deficient and normal erythrocyte host cells. Both erythrocytes infected in vitro with a laboratory isolate and erythrocytes from natural human infections were used. Total RNA was prepared from parasites collected from five G6PD-deficient and nine G6PD-normal children in Ibadan, Nigeria, selected after screening 189 rural schoolchildren and 68 clinical malaria patients, and was subjected to Northern blot analysis. The probe was a cDNA fragment of the G6PD domain of the PfG6PD-6PGL gene, with an internal control probe of P. falciparum 18S ribosomal RNA. Quantification was performed using a phosphoimager. Relative to internal control, the abundance of PfG6PD-6PGL mRNA (mean +/- standard deviation) was lower in parasites from G6PD-deficient children (0.29 +/- 0.27) than in G6PD-normal control subjects (0.74 +/- 0.26) (P = 0.014, Mann-Whitney U-test). Although confirmation in a larger study is required, our results suggest a lower relative abundance of PfG6PD-6PGL, and presumably antioxidant activity, in malaria parasites from G6PD-deficient hosts, thus extending the current knowledge of the mechanism of G6PD-deficiency related host protection.
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Affiliation(s)
- Olugbemiro Sodeinde
- Department of Haematology, Division of Investigative Science, Faculty of Medicine, Imperial College School of Medicine, Hammersmith Hospital, London W12 0NN, UK.
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89
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Salanti A, Staalsoe T, Lavstsen T, Jensen ATR, Sowa MPK, Arnot DE, Hviid L, Theander TG. Selective upregulation of a single distinctly structured var gene in chondroitin sulphate A-adhering Plasmodium falciparum involved in pregnancy-associated malaria. Mol Microbiol 2003; 49:179-91. [PMID: 12823820 DOI: 10.1046/j.1365-2958.2003.03570.x] [Citation(s) in RCA: 556] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cytoadhesion of infected red blood cells (iRBC) is mediated through parasite-encoded, clonally variant surface antigens (VSA) and is a central process in the pathogenesis of Plasmodium falciparum malaria. Pregnancy-associated malaria (PAM) has been linked to VSA-mediated adhesion of iRBC to the glycosaminoglycan chondroitin sulphate A (CSA) in the placental intervillous space. Several studies have pointed to members of the PfEMP1 VSA family as mediators of CSA-specific iRBC sequestration in the placenta. Here, we report marked upregulation of a single var gene in several P. falciparum parasite isolates after selection for adhesion to CSA in vitro. The gene belongs to a highly conserved and common var gene subfamily (var2csa). The var2csa genes are structurally distinct from all other var genes in the parasite genome in lacking both CIDR and DBL-gamma domains. These domains have previously been implicated in PfEMP1-mediated adhesion to CD36 and CSA. We also show that var2csa was transcribed at higher levels in three placental parasite isolates compared with transcription in parasites from peripheral blood of two children with P. falciparum malaria. This var gene thus has the properties expected of a gene encoding the parasite adhesion molecule that initiates the pathology associated with PAM.
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Affiliation(s)
- Ali Salanti
- Centre for Medical Parasitology at the Institute for Medical Microbiology and Immunology, University of Copenhagen, Panum Institute 24-2, and Department of Infectious Diseases, Copenhagen University Hospital (Rigshospitalet), Denmark.
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90
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Kraemer SM, Gupta L, Smith JD. New tools to identify var sequence tags and clone full-length genes using type-specific primers to Duffy binding-like domains. Mol Biochem Parasitol 2003; 129:91-102. [PMID: 12798510 DOI: 10.1016/s0166-6851(03)00099-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Cytoadherence of infected erythrocytes is a hallmark of Plasmodium falciparum infection and a key determinant in the particular virulence of this species. Infected erythrocytes bind a variety of host receptors but certain adhesion traits are associated with more severe disease. A large, diverse protein family named P. falciparum erythrocyte membrane protein 1 (PfEMP1) is responsible for sequestration of mature stage infected erythrocytes and orchestrates parasite binding tropism. To better understand the molecular basis for malaria disease, more study is needed to identify the subset of PfEMP1 variants that contribute to basic disease phenotypes. PfEMP1 proteins have multiple receptor-like domains that group into different homology types based upon sequence similarity. Universal primers have been developed that recognize some, but not all PfEMP1 adhesion domain types. In this study, we designed and validated a new series of type-discriminatory primers to the DBL-beta, -gamma, and -delta adhesion types for epidemiological profiling. In addition, we used new primers to the var upstream region and exon 2 to demonstrate how the strategic placement of primers throughout the gene structure can be exploited to efficiently clone the var gene coding region. These new approaches provide valuable tools to gain novel insights into cytoadherence and malaria pathogenesis.
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Affiliation(s)
- Susan M Kraemer
- Seattle Biomedical Research Institute, 4 Nickerson Street, Seattle, WA 98109, USA
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91
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Kyes SA, Christodoulou Z, Raza A, Horrocks P, Pinches R, Rowe JA, Newbold CI. A well-conserved Plasmodium falciparum var gene shows an unusual stage-specific transcript pattern. Mol Microbiol 2003; 48:1339-48. [PMID: 12787360 PMCID: PMC2869446 DOI: 10.1046/j.1365-2958.2003.03505.x] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The var multicopy gene family encodes Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) variant antigens, which, through their ability to adhere to a variety of host receptors, are thought to be important virulence factors. The predominant expression of a single cytoadherent PfEMP1 type on an infected red blood cell, and the switching between different PfEMP1 types to evade host protective antibody responses, are processes thought to be controlled at the transcriptional level. Contradictory data have been published on the timing of var gene transcription. Reverse transcription-polymerase chain reaction (RT-PCR) data suggested that transcription of the predominant var gene occurs in the later (pigmented trophozoite) stages, whereas Northern blot data indicated such transcripts only in early (ring) stages. We investigated this discrepancy by Northern blot, with probes covering a diverse var gene repertoire. We confirm that almost all var transcript types were detected only in ring stages. However, one type, the well-conserved varCSA transcript, was present constitutively in different laboratory parasites and does not appear to undergo antigenic variation. Although varCSA has been shown to encode a chondroitin sulphate A (CSA)-binding PfEMP1, we find that the presence of full-length varCSA transcripts does not correlate with the CSA-binding phenotype.
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Affiliation(s)
- Sue A Kyes
- Molecular Parasitology Group, Weatherall Institute of Molecular Medicine, Headington, Oxford OX3 9DS, UK.
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92
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Tami A, Ord R, Targett GAT, Sutherland CJ. Sympatric Plasmodium falciparum isolates from Venezuela have structured var gene repertoires. Malar J 2003; 2:7. [PMID: 12737636 PMCID: PMC155546 DOI: 10.1186/1475-2875-2-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2003] [Accepted: 04/11/2003] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The human malaria parasite Plasmodium falciparum expresses adhesins belonging to the erythrocyte membrane protein 1 (PfEMP1) family on the surface of the infected host erythrocyte. These antigens elicit a strain-specific antibody response that is associated with protection from disease. During clonal expansion of blood-stage parasites, the surface phenotype of the infected erythrocyte changes because of transcriptional switching among the 40 to 50 members of the highly polymorphic var multi-gene family which encode PfEMP1 variants. Studies to date have compared var repertoires of natural isolates from various geographical locations but have not addressed any within-population structure that may exist among repertoires. METHODS Distinct parasite genotypes from a single population co-circulating among a defined group of hosts were selected. PCR products encoding the DBL-alpha domain of PfEMP-1 were cloned and sequenced from each of three isolates. Repertoire similarity was statistically evaluated using combinatorial analysis. The chromosomal location of shared sequences was inferred from similarity to dbl-alpha of known location in the 3D7 genome. RESULTS Sympatric parasites were found to share few var gene sequences, even when alleles at other polymorphic loci were shared. A number of the sequences shared by at least two of the isolates studied were found to be related to 3D7 genomic sequences with non-telomeric chromosomal locations, or atypical domain structures, which may represent globally conserved loci. CONCLUSION The parasite population studied is structured, with minimal overlap in PfEMP1 repertoires. The var gene family accumulates diversity more rapidly than other antigen genes examined. This may be facilitated by ectopic recombination among the sub-telomeric regions of P. falciparum chromosomes.
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Affiliation(s)
- Adriana Tami
- Immunology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St, London, WC1E 7HT, UK
| | - Rosalynn Ord
- Immunology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St, London, WC1E 7HT, UK
| | - Geoffrey AT Targett
- Immunology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St, London, WC1E 7HT, UK
| | - Colin J Sutherland
- Immunology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St, London, WC1E 7HT, UK
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93
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Winter G, Chen Q, Flick K, Kremsner P, Fernandez V, Wahlgren M. The 3D7var5.2 (var COMMON) type var gene family is commonly expressed in non-placental Plasmodium falciparum malaria. Mol Biochem Parasitol 2003; 127:179-91. [PMID: 12672527 DOI: 10.1016/s0166-6851(03)00004-5] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Relapse variants in chronic Plasmodium falciparum infections are antigenically distinct from the parental parasites. The variable antigen PfEMP1 expressed at the surface of the infected erythrocyte (IE) is encoded by the var gene family with approximately 60 copies per haploid genome. Placental isolates commonly express DBLgamma containing subtypes of var genes with homology to either 3D7var5.2 (var(COMMON)) or FCR3var(CSA). Here we report that var(COMMON) related genes are constitutively transcribed in approximately 60% of malaria infected children in Gabon. var(COMMON) is conserved in field isolates over at least 2.1kb. In 3D7 parasites var(COMMON) is present on chromosome 5 (var5.2) and constitutively transcribed in the opposite direction to most other var genes. It lacks a regulatory intron, an acidic terminal segment and ends in telomeric repeat sequences. var(COMMON) encodes a large, hypothetical PfEMP1 of a structure similar to previous placenta-binding PfEMP1s but it is not present at the IE-surface. IE of a 3D7 clone (3D7S8) transcribe var(COMMON) but express a PfEMP1 distinct from var(COMMON) at the surface and adhere to placental tissues through var(COMMON) independent novel mechanisms. Our report suggests that expression of var(COMMON) type genes is not restricted to placental malaria.
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Affiliation(s)
- Gerhard Winter
- Microbiology and Tumor Biology Center, Karolinska Institutet, P.O. Box 280, SE-171 77, Stockholm, Sweden
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94
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Duffy MF, Reeder JC, Brown GV. Regulation of antigenic variation in Plasmodium falciparum: censoring freedom of expression? Trends Parasitol 2003; 19:121-4. [PMID: 12643994 DOI: 10.1016/s1471-4922(03)00003-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Plasmodium falciparum employs a strategy of clonal antigenic variation to evade the host immune response during the intraerythrocytic stage of its life cycle. The major variant parasite molecule is the P. falciparum erythrocyte membrane protein (PfEMP)1, which is encoded by the var multigene family. The parasite switches between different PfEMP1 molecules through regulation of var transcription. Recent studies have shed considerable light on this process, but much remains unknown. However, striking parallels between transcriptional control of var and genes in other organisms provide direction for future studies.
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Affiliation(s)
- Michael F Duffy
- Department of Medicine, The University of Melbourne, Royal Melbourne Hospital, Royal Parade, Melbourne, Victoria 3050, Australia.
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95
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Mercereau-Puijalon O, Barale JC, Bischoff E. Three multigene families in Plasmodium parasites: facts and questions. Int J Parasitol 2002; 32:1323-44. [PMID: 12350369 DOI: 10.1016/s0020-7519(02)00111-x] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Multigene families optimise fitness by providing a set of related genes with possibly different temporal and/or topological expression patterns. We analyse here the structural organisation and sequence diversity of the rDNA, sera and var C Plasmodium falciparum families, and discuss their consequences for parasite biology. The low rDNA copy number, which reduces reshuffling, is probably the corollary of the need for functionally distinct rRNAs in the insect and in the vertebrate host. The unusual intra-genome and population rDNA sequence diversity results in cells equipped with mosaic ribosome sets. The functional constraints are such that ribosome compatibility could influence parasite fitness and contribute to population structuring. Unlike the dispersed rDNA units, the sera family is arranged as a tandem gene cluster, with seven contiguous similar genes, and one more distantly related paralog. We address the question of the inclusion criteria in family definition. We discuss the results concerning the SERA proteins expression and function in the context of the long overlooked multigene family. The var C module is shared by var genes, 'orphan' var C and var C pseudogenes. Analysis of 125 var C deduced protein sequences highlights a well-conserved framework, including putative phosphorylation sites, consistent with the proposed function of mediating interaction with cytoskeletal proteins. The 5' and 3' flanking sequences of the var C pseudogenes are heterogeneous. In contrast, the flanking sequences of the uninterrupted var C modules show remarkable conservation. This is interesting in view of the silencing activity of the var intronic sequence on var expression. The 5' flanking sequence dichotomy reported for internal and sub-telomeric var genes extends to the 3' flanking sequences. This has profound implications for transcription regulation and generation of diversity. The var C family suggests a role for pseudogenes as a diversity reservoir and in genome dynamics by promoting ectopic recombination.
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Affiliation(s)
- Odile Mercereau-Puijalon
- Unité d'Immunologie Moléculaire des Parasites, Unité de Recherche Associée 1960 du Centre National de la Recherche Scientifique, Institut Pasteur, 25 rue du Dr ROUX, 75015, Paris, France.
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96
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Peters J, Fowler E, Gatton M, Chen N, Saul A, Cheng Q. High diversity and rapid changeover of expressed var genes during the acute phase of Plasmodium falciparum infections in human volunteers. Proc Natl Acad Sci U S A 2002; 99:10689-94. [PMID: 12142467 PMCID: PMC125014 DOI: 10.1073/pnas.162349899] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2001] [Accepted: 06/11/2002] [Indexed: 11/18/2022] Open
Abstract
Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) proteins expressed on the surface of P. falciparum-infected erythrocytes undergo antigenic variation by switching the gene expressed within a repertoire of approximately 50 var genes per haploid genome. The switching of PfEMP1 plays an important role in the survival and pathogenesis of the parasite. To understand how a parasite switches its var gene expression in human infections, we investigated the composition and change of var gene transcripts during the acute phase of well-defined laboratory-induced P. falciparum infections in naive human hosts. Multiple var transcripts, with the same dominant transcript, were identified in samples collected after three to four asexual-parasite cycles in two volunteers infected with cloned 3D7 P. falciparum via mosquito bites. A major change in composition and frequency of var gene transcripts was observed between the culture used to infect the mosquitoes and the parasites recovered from the infected volunteers. A further change was seen when infected blood from a mosquito-infected volunteer was either passaged to other volunteers or cultured in vitro. The diversity of var transcripts did not increase with time. The results suggest that the switch of var gene expression is reinitiated after mosquito transmission and that var genes may rapidly switch from the first gene expressed after liver stage, but subsequent switching occurs at a much lower rate.
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Affiliation(s)
- Jennifer Peters
- Malaria Laboratory, Infectious Diseases Unit, Queensland Institute of Medical Research, Post Office Royal Brisbane Hospital, Queensland 4029, Australia
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97
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Horrocks P, Pinches R, Kyes S, Kriek N, Lee S, Christodoulou Z, Newbold CI. Effect of var gene disruption on switching in Plasmodium falciparum. Mol Microbiol 2002; 45:1131-41. [PMID: 12180930 DOI: 10.1046/j.1365-2958.2002.03085.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The molecular mechanisms underpinning switching of variant antigens on the surface of Plasmodium falciparum-infected erythrocytes are poorly understood. We tested the hypothesis that insertional disruption of the A4var gene, one of two var genes located within the subtelomeric region of one end of chromosome 13, would result in a preferential switch in transcription to the adjacent R29var gene upon rosette selection. In this way, we aimed to mimic the preferential transcription of R29var in rosetting R29 parasites, a parasite line in which the A4var gene is deleted through a chromosome end truncation. Initial analysis of the knock-out parasite lines shows that the insertional disruption of the A4var gene prevents A4 PfEMP1 expression, but that switching transcription to other var gene variants is unaffected. Furthermore, analysis of var transcription in the knock-out parasite line during rosette selection shows that, rather than facilitating a switch to R29var gene transcription, this event was suppressed in the transfectants. These data, and the implications for epigenetic transcriptional control of var genes, are discussed.
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Affiliation(s)
- Paul Horrocks
- Molecular Parasitology Group, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, UK.
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98
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Vázquez-Macías A, Martínez-Cruz P, Castañeda-Patlán MC, Scheidig C, Gysin J, Scherf A, Hernández-Rivas R. A distinct 5' flanking var gene region regulates Plasmodium falciparum variant erythrocyte surface antigen expression in placental malaria. Mol Microbiol 2002; 45:155-67. [PMID: 12100556 DOI: 10.1046/j.1365-2958.2002.02999.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Plasmodium falciparum multigene var family codes for approximately 50 variant adhesive proteins expressed in a mutually exclusive manner at the surface of infected red blood cells (iRBCs). Switching expression of var genes can lead to fundamental changes in the adhesive and antigenic properties of iRBCs. For example, a specific phenotypic switch in adhesion from CD36 to chondroitin sulphate A (CSA) is associated with malaria pathogenesis in pregnant women. The factors and DNA elements that control the expression of a particular member of the var gene family during gestational malaria remains enigmatic. Here, we report that the subtelomeric FCR3 varCSA is expressed under the control of a unique DNA element of 1.8 kb, whereas the other members of the var multigene family are flanked by common regulatory elements. The 5' varCSA-type element is conserved as a single copy in laboratory strains and clinical isolates from Brazil and West Africa and contains two distinct repetitive elements of 150 bp and 60 bp respectively. The 5' varCSA-type sequence tags a var gene in the 3D7 genome that is homologous to the FCR3 varCSA gene. A recombinant DBL gamma domain of this var gene showed specific binding to CSA. This subtelomeric varCSA gene is transcribed in the opposite sense when compared with the usual orientation of telomere-adjacent var genes. This unique arrangement might explain why the varCSA gene is relatively conserved in genetically distinct parasites despite being located in a highly recombinogenic chromosome compartment. The 5' untranslated region (UTR) of the varCSA-type sequence is also transcribed in placental isolates that bind to CSA, illustrating an important role for the unique 5' varCSA-type sequence in the regulation of var genes involved in malaria pathogenesis in pregnant women. However, this promoter is not always found to be transcribing var genes selected for expression of products that bind to CSA in vitro. Our work identifies a sequence tag for the identification of varCSA genes in placental isolates for the first time.
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Affiliation(s)
- Aleida Vázquez-Macías
- Department of Molecular Biomedicine, Centro de Investigación y de Estudios Avanzados del IPN, México, D.F., Mexico
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99
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Afonso Nogueira P, Wunderlich G, Shugiro Tada M, d'Arc Neves Costa J, José Menezes M, Scherf A, Pereira-da-Silva LH. Plasmodium falciparum: analysis of transcribed var gene sequences in natural isolates from the Brazilian Amazon region. Exp Parasitol 2002; 101:111-20. [PMID: 12427465 DOI: 10.1016/s0014-4894(02)00107-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Parasite isolates from Brazilian Western Amazonian patients suffering from uncomplicated falciparum malaria were matured in vitro and their var gene transcripts were analysed by RT-PCR and sequencing. Additionally, the cytoadherence patterns of these isolates were determined by panning techniques using transfected CHO cell lines expressing different surface receptors. All of the isolates tested showed between 4 and 13 different var gene transcripts per isolate. Several of these transcripts were present in more than one isolate and three sequences appeared to be preferentially expressed in natural infections. In most of the isolates, cytoadherence occurred to the receptors ICAM-1 and CD36. Several isolates showed a multiadherent profile. Analysis of MSP1 and MSP2 allelic polymorphism indicated polyclonal infections, that could be responsible for the multiadherent phenotype.
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Affiliation(s)
- Paulo Afonso Nogueira
- Centro de Pesquisa em Medicina Tropical, CP 87, Correio Central, 78.910-210 Porto Velho, Rondônia, Brazil
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100
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Fernandez V, Chen Q, Sundström A, Scherf A, Hagblom P, Wahlgren M. Mosaic-like transcription of var genes in single Plasmodium falciparum parasites. Mol Biochem Parasitol 2002; 121:195-203. [PMID: 12034453 DOI: 10.1016/s0166-6851(02)00038-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The var gene family of Plasmodium falciparum encodes the clonally variant adhesin PfEMP1 present on the surface of infected erythrocytes. A poorly understood mechanism of allelic exclusion controls the expression of PfEMP1. Transcription of var genes is developmentally and, most likely, epigenetically regulated. Here we have studied the transcriptional pattern of 28 members of this multigene family in individual parasites, early in the intraerythrocytic cycle. The results show unique patterns (type and number) of var transcripts in each individual PRBC, with 1-15 mRNA species detected per cell at 2-4 h post-invasion. When a panel of ten single PRBC was analyzed, the var gene coding for the expressed PfEMP1 was transcribed in more cells than any other, although transcripts from this gene did not give the strongest hybridization signal within each individual cell. Chromosomal mapping of transcriptionally active var genes indicated that their distribution reflects that of var loci in the genome, including a pronounced clustering in chromosome 4. These findings, taken together with existing data on var transcription at later developmental stages, suggest that the mosaic-like transcription of multiple var genes detected at the ring stage and the steady transcription of the gene encoding the expressed PfEMP1 are distinct although superimposed events, one of them random and the other taking place under some form of imprinting. With its unique features, the expression of P. falciparum var genes may reveal new principles of gene regulation.
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Affiliation(s)
- Victor Fernandez
- Microbiology and Tumor Biology Center, Karolinska Institutet and Swedish Institute for Infectious Disease Control, Box 280, S-17177 Stockholm, Sweden.
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