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Alper CA. The Path to Conserved Extended Haplotypes: Megabase-Length Haplotypes at High Population Frequency. Front Genet 2021; 12:716603. [PMID: 34422017 PMCID: PMC8378214 DOI: 10.3389/fgene.2021.716603] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 07/13/2021] [Indexed: 11/13/2022] Open
Abstract
This minireview describes the history of the conceptual development of conserved extended haplotypes (CEHs): megabase-length haplotypes that exist at high (≥0.5%) population frequency. My career began in internal medicine, shifted to pediatrics, and clinical practice changed to research. My research interest was initially in hematology: on plasma proteins, their metabolism, synthesis, and function. This narrowed to a focus on proteins of the human complement system, their role in immunity and their genetics, beginning with polymorphism and deficiency of C3. My group identified genetic polymorphisms and/or inherited deficiencies of C2, C4, C6, and C8. After defining glycine-rich beta glycoprotein as factor B (Bf) in the properdin system, we found that the genes for Bf (CFB), C2, C4A, and C4B were inherited as a single haplotypic unit which we named the "complotype." Complotypes are located within the major histocompatibility complex (MHC) between HLA-B and HLA-DRB1 and are designated (in arbitrary order) by their CFB, C2, C4A, and C4B types. Pedigree analysis revealed long stretches (several megabases) of apparently fixed DNA within the MHC that we referred to as "extended haplotypes" (later as "CEHs"). About 10 to 12 common CEHs constitute at least 25 - 30% of MHC haplotypes among European Caucasian populations. These CEHs contain virtually all the most common markers of MHC-associated diseases. In the case of type 1 diabetes, we have proposed a purely genetic and epigenetic model (with a small number of Mendelian recessive disease genes) that explains all the puzzling features of the disease, including its rising incidence.
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Affiliation(s)
- Chester A Alper
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, United States.,Department of Pediatrics, Harvard Medical School, Boston, MA, United States
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2
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Creary LE, Sacchi N, Mazzocco M, Morris GP, Montero-Martin G, Chong W, Brown CJ, Dinou A, Stavropoulos-Giokas C, Gorodezky C, Narayan S, Periathiruvadi S, Thomas R, De Santis D, Pepperall J, ElGhazali GE, Al Yafei Z, Askar M, Tyagi S, Kanga U, Marino SR, Planelles D, Chang CJ, Fernández-Viña MA. High-resolution HLA allele and haplotype frequencies in several unrelated populations determined by next generation sequencing: 17th International HLA and Immunogenetics Workshop joint report. Hum Immunol 2021; 82:505-522. [PMID: 34030896 DOI: 10.1016/j.humimm.2021.04.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 04/23/2021] [Accepted: 04/28/2021] [Indexed: 12/12/2022]
Abstract
The primary goal of the unrelated population HLA diversity (UPHD) component of the 17th International HLA and Immunogenetics Workshop was to characterize HLA alleles at maximum allelic-resolution in worldwide populations and re-evaluate patterns of HLA diversity across populations. The UPHD project included HLA genotype and sequence data, generated by various next-generation sequencing methods, from 4,240 individuals collated from 12 different countries. Population data included well-defined large datasets from the USA and smaller samples from Europe, Australia, and Western Asia. Allele and haplotype frequencies varied across populations from distant geographical regions. HLA genetic diversity estimated at 2- and 4-field allelic resolution revealed that diversity at the majority of loci, particularly for European-descent populations, was lower at the 2-field resolution. Several common alleles with identical protein sequences differing only by intronic substitutions were found in distinct haplotypes, revealing a more detailed characterization of linkage between variants within the HLA region. The examination of coding and non-coding nucleotide variation revealed many examples in which almost complete biunivocal relations between common alleles at different loci were observed resulting in higher linkage disequilibrium. Our reference data of HLA profiles characterized at maximum resolution from many populations is useful for anthropological studies, unrelated donor searches, transplantation, and disease association studies.
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Affiliation(s)
- Lisa E Creary
- Department of Pathology, Stanford University School of Medicine, Palo Alto, CA, USA; Histocompatibility and Immunogenetics Laboratory, Stanford Blood Center, Palo Alto CA, USA.
| | - Nicoletta Sacchi
- Italian Bone Marrow Donor Registry Tissue Typing Laboratory, E.O. Ospedali Galliera, Genova, Italy
| | - Michela Mazzocco
- Italian Bone Marrow Donor Registry Tissue Typing Laboratory, E.O. Ospedali Galliera, Genova, Italy
| | - Gerald P Morris
- Department of Pathology, University of California San Diego, La Jolla, CA, USA
| | - Gonzalo Montero-Martin
- Histocompatibility and Immunogenetics Laboratory, Stanford Blood Center, Palo Alto CA, USA
| | - Winnie Chong
- Histocompatibility and Immunogenetics Service Development Laboratory, NHS Blood and Transplant, London, UK
| | - Colin J Brown
- Department of Histocompatibility and Immunogenetics, NHS Blood and Transplant, London, UK; Faculty of Life Sciences and Medicine, King's College London, University of London, England, UK
| | - Amalia Dinou
- Biomedical Research Foundation Academy of Athens, Hellenic Cord Blood Bank, Athens, Greece
| | | | - Clara Gorodezky
- Laboratory of Immunology and Immunogenetics, Fundación Comparte Vida, A.C. Mexico City, Mexico
| | | | | | - Rasmi Thomas
- US Military HIV Research Program, Walter Reed Army Institute of Research, Silver Spring, USA
| | | | - Jennifer Pepperall
- Welsh Transplant and Immunogenetics Laboratory, Welsh Blood Service, Pontyclun, United Kingdom
| | - Gehad E ElGhazali
- Sheikh Khalifa Medical City-Union 71, Abu Dhabi and the Department of Immunology, College of Medicine and Health Sciences, UAE University, Al Ain, United Arab Emirates
| | - Zain Al Yafei
- Sheikh Khalifa Medical City-Union 71, Abu Dhabi and the Department of Immunology, College of Medicine and Health Sciences, UAE University, Al Ain, United Arab Emirates
| | - Medhat Askar
- Department of Pathology and Laboratory Medicine, Baylor University Medical center, Dallas, USA
| | - Shweta Tyagi
- Department of Transplant Immunology and Immunogenetics, All India Institute of Medical Sciences, New Delhi, India
| | - Uma Kanga
- Department of Transplant Immunology and Immunogenetics, All India Institute of Medical Sciences, New Delhi, India
| | - Susana R Marino
- Department of Pathology, The University of Chicago Medicine, Chicago, IL, USA
| | - Dolores Planelles
- Histocompatibility, Centro de Transfusión de la Comunidad Valenciana, Valencia, Spain; Grupo Español de Trabajo en Histocompatibilidad e Inmunología del Trasplante (GETHIT), Spanish Society for Immunology, Madrid, Spain
| | | | - Marcelo A Fernández-Viña
- Department of Pathology, Stanford University School of Medicine, Palo Alto, CA, USA; Histocompatibility and Immunogenetics Laboratory, Stanford Blood Center, Palo Alto CA, USA.
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Buhler S, Baldomero H, Ferrari-Lacraz S, Nunes JM, Sanchez-Mazas A, Massouridi-Levrat S, Heim D, Halter J, Nair G, Chalandon Y, Schanz U, Güngör T, Nicoloso G, Tiercy JM, Passweg J, Villard J. High-resolution HLA phased haplotype frequencies to predict the success of unrelated donor searches and clinical outcome following hematopoietic stem cell transplantation. Bone Marrow Transplant 2019; 54:1701-9. [PMID: 30953025 DOI: 10.1038/s41409-019-0520-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 03/18/2019] [Indexed: 02/06/2023]
Abstract
HLA matching is a critical factor for successful allogeneic hematopoietic stem cell transplantation. For unrelated donor searches, matching is usually based on high-resolution typing at five HLA loci, looking for a 10/10 match. Some studies have proposed that further matching at the haplotype level could be beneficial for clinical outcome. In this study, we determined the phased haplotypes of 291 patients using family members and segregation analysis. The sum of ranks of the haplotypes carried by patients was used as a surrogate predictor of a successful unrelated donor search. The putative impact of haplotypes was then analyzed in a cohort of 211 recipients transplanted with 10/10 matched unrelated donors. A logistic regression analysis showed a highly significant effect of the haplotypes in the outcome of a search, but we did not find any significant effect on overall survival, graft versus host disease or relapse/progression following HSCT. This study provides useful data for the optimization of unrelated bone marrow donor searches, but does not confirm previous reports that matching at the haplotype level has a clinical impact following HSCT. Due to the extreme polymorphism of HLA genes, further studies are warranted to better understand the many factors at play.
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Goeury T, Creary LE, Brunet L, Galan M, Pasquier M, Kervaire B, Langaney A, Tiercy JM, Fernández-Viña MA, Nunes JM, Sanchez-Mazas A. Deciphering the fine nucleotide diversity of full HLA class I and class II genes in a well-documented population from sub-Saharan Africa. HLA 2019; 91:36-51. [PMID: 29160618 PMCID: PMC5767763 DOI: 10.1111/tan.13180] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Revised: 11/01/2017] [Accepted: 11/15/2017] [Indexed: 01/06/2023]
Abstract
With the aim to understand how next‐generation sequencing (NGS) improves both our assessment of genetic variation within populations and our knowledge on HLA molecular evolution, we sequenced and analysed 8 HLA loci in a well‐documented population from sub‐Saharan Africa (Mandenka). The results of full‐gene NGS‐MiSeq sequencing compared with those obtained by traditional typing techniques or limited sequencing strategies showed that segregating sites located outside exon 2 are crucial to describe not only class I but also class II population diversity. A comprehensive analysis of exons 2, 3, 4 and 5 nucleotide diversity at the 8 HLA loci revealed remarkable differences among these gene regions, notably a greater variation concentrated in the antigen recognition sites of class I exons 3 and some class II exons 2, likely associated with their peptide‐presentation function, a lower diversity of HLA‐C exon 3, possibly related to its role as a KIR ligand, and a peculiar molecular diversity of HLA‐A exon 2, revealing demographic signals. Based on full‐length HLA sequences, we also propose that the most frequent DRB1 allele in the studied population, DRB1*13:04, emerged from an allelic conversion involving 3 potential alleles as donors and DRB1*11:02:01 as recipient. Finally, our analysis revealed a high occurrence of the DRB1*13:04‐DQA1*05:05:01‐DQB1*03:19 haplotype, possibly resulting from a selective sweep due to protection to Onchorcerca volvulus, a prevalent pathogen in West Africa. This study unveils highly relevant information on the molecular evolution of HLA genes in relation to their immune function, calling for similar analyses in other populations living in contrasting environments.
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Affiliation(s)
- T Goeury
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva, University of Geneva, Geneva, Switzerland
| | - L E Creary
- Department of Pathology, Stanford University School of Medicine, Palo Alto, California
| | - L Brunet
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva, Switzerland.,Transplantation Immunology Unit and National Reference Laboratory for Histocompatibility (UIT/LNRH), Geneva University Hospital, Geneva, Switzerland
| | - M Galan
- INRA, UMR 1062 CBGP, avenue du Campus Agropolis, Montferrier sur Lez, France
| | - M Pasquier
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva, University of Geneva, Geneva, Switzerland
| | - B Kervaire
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva, Switzerland.,Transplantation Immunology Unit and National Reference Laboratory for Histocompatibility (UIT/LNRH), Geneva University Hospital, Geneva, Switzerland
| | - A Langaney
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva, Switzerland
| | - J-M Tiercy
- Institute of Genetics and Genomics in Geneva, University of Geneva, Geneva, Switzerland.,Transplantation Immunology Unit and National Reference Laboratory for Histocompatibility (UIT/LNRH), Geneva University Hospital, Geneva, Switzerland
| | - M A Fernández-Viña
- Department of Pathology, Stanford University School of Medicine, Palo Alto, California
| | - J M Nunes
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva, University of Geneva, Geneva, Switzerland
| | - A Sanchez-Mazas
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva, University of Geneva, Geneva, Switzerland
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Goodin DS, Khankhanian P, Gourraud PA, Vince N. Highly conserved extended haplotypes of the major histocompatibility complex and their relationship to multiple sclerosis susceptibility. PLoS One 2018; 13:e0190043. [PMID: 29438392 PMCID: PMC5810982 DOI: 10.1371/journal.pone.0190043] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 12/07/2017] [Indexed: 12/03/2022] Open
Abstract
Objective To determine the relationship between highly-conserved extended-haplotypes (CEHs) in the major histocompatibility complex (MHC) and MS-susceptibility. Background Among the ~200 MS-susceptibility regions, which are known from genome-wide analyses of single nucleotide polymorphisms (SNPs), the MHC accounts for roughly a third of the currently explained variance and the strongest MS-associations are for certain Class II alleles (e.g., HLA-DRB1*15:01; HLA-DRB1*03:01; and HLA-DRB1*13:03), which frequently reside on CEHs within the MHC. Design/Methods Autosomal SNPs (441,547) from 11,376 MS cases and 18,872 controls in the WTCCC dataset were phased. The most significant MS associated SNP haplotype was composed of 11 SNPs in the MHC Class II region surrounding the HLA-DRB1 gene. We also phased alleles at the HLA-A, HLA-C, HLA-B, HLA-DRB1, and HLA-DQB1 loci. This data was used to probe the relationship between CEHs and MS susceptibility. Results We phased a total of 59,884 extended haplotypes (HLA-A, HLA-C, HLA-B, HLA-DRB1, HLA-DQB1 and SNP haplotypes) from 29,942 individuals. Of these, 10,078 unique extended haplotypes were identified. The 10 most common CEHs accounted for 22% (13,302) of the total. By contrast, the 8,446 least common extended haplotypes also accounted for approximately 20% (12,298) of the total. This extreme frequency-disparity among extended haplotypes necessarily complicates interpretation of reported disease-associations with specific HLA alleles. In particular, the HLA motif HLA-DRB1*15:01~HLA-DQB1*06:02 is strongly associated with MS risk. Nevertheless, although this motif is almost always found on the a1 SNP haplotype, it can rarely be found on others (e.g., a27 and a36), and, in these cases, it seems to have no apparent disease-association (OR = 0.7; CI = 0.3–1.3 and OR = 0.7; CI = 0.2–2.2, respectively). Furthermore, single copy carriers of the a1 SNP-haplotype without this HLA motif still have an increased disease risk (OR = 2.2; CI = 1.2–3.8). In addition, even among the set of CEHs, which carry the Class II motif of HLA-DRB1*15:01~HLA-DQB1*06:02~a1, different CEHs have differing strengths in their MS-associations. Conclusions The MHC in diverse human populations consists, primarily, of a very small collection of very highly-selected CEHs. Our findings suggest that the MS-association with the HLA-DRB1*15:01~HLA-DQB1*06:02 haplotype may be due primarily to the combined attributes of the CEHs on which this particular HLA-motif often resides.
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Affiliation(s)
- Douglas S. Goodin
- Department of Neurology, University of California, San Francisco, CA, United States of America
- * E-mail:
| | - Pouya Khankhanian
- Center for Neuro-engineering and Therapeutics, University of Pennsylvania, Philadelphia, PA, United States of America
| | - Pierre-Antoine Gourraud
- Department of Neurology, University of California, San Francisco, CA, United States of America
- Centre de Recherche en Transplantation et Immunologie UMR 1064, INSERM, Université de Nantes, Nantes, France
- Institut de Transplantation Urologie Néphrologie (ITUN), CHU Nantes, Nantes, France
| | - Nicolas Vince
- Centre de Recherche en Transplantation et Immunologie UMR 1064, INSERM, Université de Nantes, Nantes, France
- Institut de Transplantation Urologie Néphrologie (ITUN), CHU Nantes, Nantes, France
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Sanchez-Mazas A, Černý V, Di D, Buhler S, Podgorná E, Chevallier E, Brunet L, Weber S, Kervaire B, Testi M, Andreani M, Tiercy JM, Villard J, Nunes JM. The HLA-B landscape of Africa: Signatures of pathogen-driven selection and molecular identification of candidate alleles to malaria protection. Mol Ecol 2017; 26:6238-6252. [PMID: 28950417 DOI: 10.1111/mec.14366] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Accepted: 09/11/2017] [Indexed: 11/30/2022]
Abstract
Human leukocyte antigen (HLA) genes play a key role in the immune response to infectious diseases, some of which are highly prevalent in specific environments, like malaria in sub-Saharan Africa. Former case-control studies showed that one particular HLA-B allele, B*53, was associated with malaria protection in Gambia, but this hypothesis was not tested so far within a population genetics framework. In this study, our objective was to assess whether pathogen-driven selection associated with malaria contributed to shape the HLA-B genetic landscape of Africa. To that aim, we first typed the HLA-A and -B loci in 484 individuals from 11 populations living in different environments across the Sahel, and we analysed these data together with those available for 29 other populations using several approaches including linear modelling on various genetic, geographic and environmental parameters. In addition to relevant signatures of populations' demography and migrations history in the genetic differentiation patterns of both HLA-A and -B loci, we found that the frequencies of three HLA alleles, B*53, B*78 and A*74, were significantly associated with Plasmodium falciparum malaria prevalence, suggesting their increase through pathogen-driven selection in malaria-endemic environments. The two HLA-B alleles were further identified, by high-throughput sequencing, as B*53:01:01 (in putative linkage disequilibrium with one HLA-C allele, C*04:01:01:01) and B*78:01 in all but one individuals tested, making them appropriate candidates to malaria protection. These results highlight the role of environmental factors in the evolution of the HLA polymorphism and open key perspectives for functional studies focusing on HLA peptide-binding properties.
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Affiliation(s)
- Alicia Sanchez-Mazas
- Department of Genetics and Evolution - Anthropology Unit, Laboratory of Anthropology, Genetics and Peopling History (AGP), University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva (IGE3), Geneva, Switzerland
| | - Viktor Černý
- Department of Anthropology and Human Genetics, Faculty of Science, Charles University, Prague, Czech Republic
| | - Da Di
- Department of Genetics and Evolution - Anthropology Unit, Laboratory of Anthropology, Genetics and Peopling History (AGP), University of Geneva, Geneva, Switzerland
| | - Stéphane Buhler
- Department of Genetics and Evolution - Anthropology Unit, Laboratory of Anthropology, Genetics and Peopling History (AGP), University of Geneva, Geneva, Switzerland.,Department of Genetic and Laboratory Medicine, Transplantation Immunology Unit and National Reference Laboratory for Histocompatibility (UIT/LNRH), Geneva University Hospitals, Geneva, Switzerland
| | - Eliška Podgorná
- Department of the Archaeology of Landscape and Archaeobiology, Archaeogenetics Laboratory, Institute of Archaeology of the Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Elodie Chevallier
- Department of Genetics and Evolution - Anthropology Unit, Laboratory of Anthropology, Genetics and Peopling History (AGP), University of Geneva, Geneva, Switzerland
| | - Lydie Brunet
- Department of Genetics and Evolution - Anthropology Unit, Laboratory of Anthropology, Genetics and Peopling History (AGP), University of Geneva, Geneva, Switzerland.,Department of Genetic and Laboratory Medicine, Transplantation Immunology Unit and National Reference Laboratory for Histocompatibility (UIT/LNRH), Geneva University Hospitals, Geneva, Switzerland
| | - Stephan Weber
- Department of Genetics and Evolution - Anthropology Unit, Laboratory of Anthropology, Genetics and Peopling History (AGP), University of Geneva, Geneva, Switzerland
| | - Barbara Kervaire
- Department of Genetic and Laboratory Medicine, Transplantation Immunology Unit and National Reference Laboratory for Histocompatibility (UIT/LNRH), Geneva University Hospitals, Geneva, Switzerland
| | - Manuela Testi
- Laboratory of Immunogenetics and Transplant Biology, IME Foundation, Policlinic of the University of Tor Vergata, Rome, Italy
| | - Marco Andreani
- Laboratory of Immunogenetics and Transplant Biology, IME Foundation, Policlinic of the University of Tor Vergata, Rome, Italy
| | - Jean-Marie Tiercy
- Institute of Genetics and Genomics in Geneva (IGE3), Geneva, Switzerland.,Department of Genetic and Laboratory Medicine, Transplantation Immunology Unit and National Reference Laboratory for Histocompatibility (UIT/LNRH), Geneva University Hospitals, Geneva, Switzerland
| | - Jean Villard
- Institute of Genetics and Genomics in Geneva (IGE3), Geneva, Switzerland.,Department of Genetic and Laboratory Medicine, Transplantation Immunology Unit and National Reference Laboratory for Histocompatibility (UIT/LNRH), Geneva University Hospitals, Geneva, Switzerland
| | - José Manuel Nunes
- Department of Genetics and Evolution - Anthropology Unit, Laboratory of Anthropology, Genetics and Peopling History (AGP), University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva (IGE3), Geneva, Switzerland
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Buhler S, Nunes JM, Sanchez-Mazas A. HLA class I molecular variation and peptide-binding properties suggest a model of joint divergent asymmetric selection. Immunogenetics 2016; 68:401-416. [PMID: 27233953 PMCID: PMC4911380 DOI: 10.1007/s00251-016-0918-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 05/17/2016] [Indexed: 01/20/2023]
Abstract
The main function of HLA class I molecules is to present pathogen-derived peptides to cytotoxic T lymphocytes. This function is assumed to drive the maintenance of an extraordinary amount of polymorphism at each HLA locus, providing an immune advantage to heterozygote individuals capable to present larger repertories of peptides than homozygotes. This seems contradictory, however, with a reduced diversity at individual HLA loci exhibited by some isolated populations. This study shows that the level of functional diversity predicted for the two HLA-A and HLA-B genes considered simultaneously is similar (almost invariant) between 46 human populations, even when a reduced diversity exists at each locus. We thus propose that HLA-A and HLA-B evolved through a model of joint divergent asymmetric selection conferring all populations an equivalent immune potential. The distinct pattern observed for HLA-C is explained by its functional evolution towards killer cell immunoglobulin-like receptor (KIR) activity regulation rather than peptide presentation.
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Affiliation(s)
- Stéphane Buhler
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution, Anthropology Unit, University of Geneva, Geneva, Switzerland. .,Transplantation Immunology Unit & National Reference Laboratory for Histocompatibility, Department of Genetic and Laboratory Medicine, Geneva University Hospital, Geneva, Switzerland.
| | - José Manuel Nunes
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution, Anthropology Unit, University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva (iGE3), University of Geneva, Geneva, Switzerland
| | - Alicia Sanchez-Mazas
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution, Anthropology Unit, University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva (iGE3), University of Geneva, Geneva, Switzerland
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Abstract
MS-pathogenesis involves both genetic-susceptibility and environmental determinants. Three (or more) sequential environmental-factors are implicated. The first acts near birth, the second acts during childhood/adolescence, and the third acts subsequently. Two candidate factors (vitamin D deficiency and Epstein-Barr viral infection) seem particularly well-suited to the first two environmental-events but other factors (e.g., obesity and smoking behavior) seem also to be involved in the causal scheme. MS-pathogenesis can be modeled by incorporating both the environmental and genetic-factors into a causal scheme, which can then help to explain some of the changes in MS-epidemiology (e.g., increasing disease-prevalence, changing sex-ratio, and regional-variations in monozygotic-twin-concordance-rates), which have been taking place recently. This model suggests that genetic-susceptibility is overwhelmingly the most important determinant of MS and that, at least, 92.5% of individuals (and likely much more) are, essentially, incapable of developing MS, regardless of their specific environmental-exposures. Nevertheless, the genetics is complex and the contribution of any specific gene to MS-susceptibility seems to be quite modest. Thus, even for the DRB1*1501 allele (the strongest known MS-susceptibility marker), most carriers are not in the genetically-susceptible group. Moreover, 45-50% of individuals with MS lack this allele entirely and some of the haplotypes that carry this allele don't also confer any disease-risk. Finally, because the prevalence of genetic-susceptibility seems to be so similar throughout North America and Europe, and despite the crucial importance of a person's genetic make-up to disease pathogenesis, it is the environmental-factors, which largely responsible for the observed regional variations in disease-characteristics. Thus, despite MS being more common in women, men are more likely to be genetically-susceptible. This apparent paradox seems to relate to the fact that women are much more responsive than men to the recent changes in environmental-exposure (whatever these have been). These gender-differences may help to explain changes in the sex-ratio and the increasing disease-prevalence, which have both been observed recently. The potential importance of these conclusions regarding the role of environment in MS-pathogenesis is that they open the door to the possibility of pursuing strategies for primary primary disease prevention in the future.
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Affiliation(s)
- D S Goodin
- Multiple Sclerosis Center at the University of California, San Francisco, San Francisco, CA, USA.
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