The essential malaria protein PfCyRPA targets glycans to invade erythrocytes

Plasmodium falciparum is a human-adapted apicomplexan parasite that causes the most dangerous form of malaria. P. falciparum cysteine-rich protective antigen (PfCyRPA) is an invasion complex protein essential for erythrocyte invasion. The precise role of PfCyRPA in this process has not been resolved. Here, we show that PfCyRPA is a lectin targeting glycans terminating with α2-6-linked N-acetylneuraminic acid (Neu5Ac). PfCyRPA has a >50-fold binding preference for human, α2-6-linked Neu5Ac over non-human, α2-6-linked N-glycolylneuraminic acid. PfCyRPA lectin sites were predicted by molecular modeling and validated by mutagenesis studies. Transgenic parasite lines expressing endogenous PfCyRPA with single amino acid exchange mutants indicated that the lectin activity of PfCyRPA has an important role in parasite invasion. Blocking PfCyRPA lectin activity with small molecules or with lectin-site-specific monoclonal antibodies can inhibit blood-stage parasite multiplication. Therefore, targeting PfCyRPA lectin activity with drugs, immunotherapy, or a vaccine-primed immune response is a promising strategy to prevent and treat malaria.

Analysis of nucleic acids extracted from rapid diagnostic tests reveals a significant proportion of false positive test results associated with recent malaria treatment

BACKGROUND

Surveillance programmes often use malaria rapid diagnostic tests (RDTs) to determine the proportion of the population carrying parasites in their peripheral blood to assess the malaria transmission intensity. Despite an increasing number of reports on false-negative and false-positive RDT results, there is a lack of systematic quality control activities for RDTs deployed in malaria surveillance programmes.

METHODS

The diagnostic performance of field-deployed RDTs used for malaria surveys was assessed by retrospective molecular analysis of the blood retained on the tests.

RESULTS

Of the 2865 RDTs that were collected in 2018 on Bioko Island and analysed in this study, 4.7% had a false-negative result. These false-negative RDTs were associated with low parasite density infections. In 16.6% of analysed samples, masked pfhrp2 and pfhrp3 gene deletions were identified, in which at least one Plasmodium falciparum strain carried a gene deletion. Among all positive RDTs analysed, 28.4% were tested negative by qPCR and therefore considered to be false-positive. Analysing the questionnaire data collected from the participants, this high proportion of false-positive RDTs could be explained by P. falciparum histidine rich protein 2 (PfHRP2) antigen persistence after recent malaria treatment.

CONCLUSION

Malaria surveillance depending solely on RDTs needs well-integrated quality control procedures to assess the extent and impact of reduced sensitivity and specificity of RDTs on malaria control programmes.

An Antigen Capture Assay for the Detection of Mycolactone, the Polyketide Toxin of Mycobacterium ulcerans

Mycolactone is a cytotoxin responsible for most of the chronic necrotizing pathology of Mycobacterium ulcerans disease (Buruli ulcer). The polyketide toxin consists of a 12-membered lactone ring with a lower O-linked polyunsaturated acyl side chain and an upper C-linked side chain. Mycolactone is unique to M. ulcerans and an immunological Ag capture assay would represent an important tool for the study of Buruli ulcer pathogenesis and for laboratory diagnosis. When testing sets of mycolactone-specific mouse mAbs, we found that Abs against the hydrophobic lower side chain only bind mycolactone immobilized on a solid support but not when present in solution. This observation supports previous findings that mycolactone forms micellar structures in aqueous solution with the hydrophobic region sequestered into the inner core of the aggregates. Although an Ag capture assay typically requires two Abs that recognize nonoverlapping epitopes, our search for matching pairs of mAbs showed that the same mAb could be used both as capture and as detecting reagent for the detection of the mycolactone aggregates. However, the combination of a core-specific and a core/upper side chain-specific mAb constituted the most sensitive ELISA with a sensitivity in the low nanogram range. The results of a pilot experiment showed that the sensitivity of the assay is sufficient to detect mycolactone in swab samples from Buruli ulcer lesions. Although the described capture ELISA can serve as a tool for research on the biology of mycolactone, the assay system will have to be adapted for use as a diagnostic tool.

Role of human Pegivirus infections in whole Plasmodium falciparum sporozoite vaccination and controlled human malaria infection in African volunteers

BACKGROUND

Diverse vaccination outcomes and protection levels among different populations pose a serious challenge to the development of an effective malaria vaccine. Co-infections are among many factors associated with immune dysfunction and sub-optimal vaccination outcomes. Chronic, asymptomatic viral infections can contribute to the modulation of vaccine efficacy through various mechanisms. Human Pegivirus-1 (HPgV-1) persists in immune cells thereby potentially modulating immune responses. We investigated whether Pegivirus infection influences vaccine-induced responses and protection in African volunteers undergoing whole P. falciparum sporozoites-based malaria vaccination and controlled human malaria infections (CHMI).

METHODS

HPgV-1 prevalence was quantified by RT-qPCR in plasma samples of 96 individuals before, post vaccination with PfSPZ Vaccine and after CHMI in cohorts from Tanzania and Equatorial Guinea. The impact of HPgV-1 infection was evaluated on (1) systemic cytokine and chemokine levels measured by Luminex, (2) PfCSP-specific antibody titers quantified by ELISA, (3) asexual blood-stage parasitemia pre-patent periods and parasite multiplication rates, (4) HPgV-1 RNA levels upon asexual blood-stage parasitemia induced by CHMI.

RESULTS

The prevalence of HPgV-1 was 29.2% (28/96) and sequence analysis of the 5' UTR and E2 regions revealed the predominance of genotypes 1, 2 and 5. HPgV-1 infection was associated with elevated systemic levels of IL-2 and IL-17A. Comparable vaccine-induced anti-PfCSP antibody titers, asexual blood-stage multiplication rates and pre-patent periods were observed in HPgV-1 positive and negative individuals. However, a tendency for higher protection levels was detected in the HPgV-1 positive group (62.5%) compared to the negative one (51.6%) following CHMI. HPgV-1 viremia levels were not significantly altered after CHMI.

CONCLUSIONS

HPgV-1 infection did not alter PfSPZ Vaccine elicited levels of PfCSP-specific antibody responses and parasite multiplication rates. Ongoing HPgV-1 infection appears to improve to some degree protection against CHMI in PfSPZ-vaccinated individuals. This is likely through modulation of immune system activation and systemic cytokines as higher levels of IL-2 and IL17A were observed in HPgV-1 infected individuals. CHMI is safe and well tolerated in HPgV-1 infected individuals. Identification of cell types and mechanisms of both silent and productive infection in individuals will help to unravel the biology of this widely present but largely under-researched virus.

Performance of a real-time PCR approach for diagnosing Schistosoma haematobium infections of different intensity in urine samples from Zanzibar

Background

Efforts to control and eliminate schistosomiasis have accelerated over the past decade. As parasite burden, associated morbidity and egg excretion decrease, diagnosis with standard parasitological methods becomes harder. We assessed the robustness and performance of a real-time PCR (qPCR) approach in comparison with urine filtration microscopy and reagent strip testing for the diagnosis of Schistosoma haematobium infections of different intensities.

Methods

The robustness of DNA isolation and qPCR was validated in eight laboratories from Europe and Africa. Subsequently, 792 urine samples collected during cross-sectional surveys of the Zanzibar Elimination of Schistosomiasis Transmission (ZEST) project in 2012–2017 were examined with qPCR in 2018. Diagnostic sensitivity of the qPCR was calculated at different infection intensity categories, using urine filtration microscopy as reference test. Spearman’s rank correlation between Ct-values and S. haematobium egg counts was assessed and Ct-value percentiles for infection intensity categories determined.

Results

S. haematobium Dra1 DNA-positive samples were identified correctly in all eight laboratories. Examination of urine samples from Zanzibar revealed Dra1 DNA in 26.8% (212/792) by qPCR, S. haematobium eggs in 13.3% (105/792) by urine filtration, and microhaematuria in 13.8% (109/792) by reagent strips. Sensitivity of the qPCR increased with augmenting egg counts: 80.6% (29/36) for counts between 1 and 4 eggs, 83.3% (15/18) for counts between 5 and 9 eggs, 100% (23/23) for counts between 10 and 49 eggs, and 96.4% (27/28) for counts of 50+ eggs. There was a significant negative correlation between Ct-values and egg counts (Spearman’s rho = − 0.49, P < 0.001). Seventy-five percent of the Ct-values were ≥ 33 in the egg-negative category, < 31 in the light intensity category, and < 24 in the heavy intensity category.

Conclusions

While the sensitivity of the qPCR was ~ 80% for very light intensity infections (egg counts < 10), in general, the Dra1 based qPCR assay detected twice as many S. haematobium infections compared with classical parasitological tests. The qPCR is hence a sensitive, urine-based approach for S. haematobium diagnosis that can be used for impact assessment of schistosomiasis elimination programmes, individual diagnosis, and in improved format also for verification and certification of elimination.

Trial registration

ISRCTN, ISRCTN48837681. Registered 05 September 2012 - Retrospectively registered.

Development of an ELISA for the quantification of mycolactone, the cytotoxic macrolide toxin of Mycobacterium ulcerans

Mycolactones, macrolide cytotoxins, are key virulence factors of Mycobacterium ulcerans, the etiological agent of the chronic necrotizing skin disease Buruli ulcer. There is urgent need for a simple point-of-care laboratory test for Buruli ulcer and mycolactone represents a promising target for the development of an immunological assay. However, for a long time, all efforts to generate mycolactone-specific antibodies have failed. By using a protein conjugate of a truncated non-toxic synthetic mycolactone derivative, we recently described generation of a set of mycolactone-specific monoclonal antibodies. Using the first mycolactone-specific monoclonal antibodies that we have described before, we were able to develop an antigen competition assay that detects mycolactones. By the systematic selection of a capturing antibody and a reporter molecule, and the optimization of assay conditions, we developed an ELISA that detects common natural variants of mycolactone with a limit of detection in the low nanomolar range. The mycolactone-specific ELISA described here will be a very useful tool for research on the biology of this macrolide toxin. After conversion into a simple point-of-care test format, the competition assay may have great potential as laboratory assay for both the diagnosis of Buruli ulcer and for the monitoring of treatment efficacy.

Activation of TCR Vδ1+ and Vδ1-Vδ2- γδ T Cells upon Controlled Infection with Plasmodium falciparum in Tanzanian Volunteers

Our understanding of the human immune response to malaria remains incomplete. Clinical trials using whole-sporozoite-based vaccination approaches such as the Sanaria PfSPZ Vaccine, followed by controlled human malaria infection (CHMI) to assess vaccine efficacy offer a unique opportunity to study the immune response during Plasmodium falciparum infection. Diverse populations of T cells that are not restricted to classical HLA (unconventional T cells) participate in the host response during Plasmodium infection. Although several populations of unconventional T cells exist, the majority of studies focused on TCR Vγ9Vδ2 cells, the most abundant TCR γδ cell population in peripheral blood. In this study, we dissected the response of three TCR γδ cell subsets and mucosal-associated invariant T cells in healthy volunteers immunized with PfSPZ Vaccine and challenged by CHMI using Sanaria PfSPZ Challenge. Using a flow cytometry-based unbiased analysis followed by T cell cloning, several findings were made. Whereas major ex vivo alterations were not detectable after immunization with PfSPZ Vaccine, TCR Vδ2, and mucosal-associated invariant T cells expanded after asexual blood-stage parasitemia induced by CHMI. CHMI, but not vaccination, also induced the activation of TCR Vδ1 and Vδ1^-Vδ2^- γδ T cells. The activated TCR Vδ1 cells were oligoclonal, suggesting clonal expansion, and upon repeated CHMI, showed diminished response, indicating long-term alterations induced by blood-stage parasitemia. Some TCR Vδ1 clones recognized target cells in the absence of parasite-derived Ags, thus suggesting recognition of self-molecules. These findings reveal the articulate participation of different populations of unconventional T cells to P. falciparum infection.

Configurationally Stabilized Analogs of M. ulcerans Exotoxins Mycolactones A and B Reveal the Importance of Side Chain Geometry for Mycolactone Virulence

Mycolactones A/B (1a/b) are exotoxins of Mycobacterium ulcerans that are the molecular cause of Buruli ulcer. 1a/b represent a rapidly equilibrating mixture of Z/E isomers about the C4'═C5' double bond of the C5-side chain. Here, we describe the syntheses of mycolactone analogs with configurationally stable C5-side chains (2a, E mimetic; 2b/c, Z mimetics). Based on the cytotoxicity of 2a-c, the Δ^4',5'-trans isomer of mycolactones A/B (1b) appears to be the major virulence factor.

Loss of Genomic Diversity in a Neisseria meningitidis Clone Through a Colonization Bottleneck

Neisseria meningitidis is the leading cause of epidemic meningitis in the "meningitis belt" of Africa, where clonal waves of colonization and disease are observed. Point mutations and horizontal gene exchange lead to constant diversification of meningococcal populations during clonal spread. Maintaining a high genomic diversity may be an evolutionary strategy of meningococci that increases chances of fixing occasionally new highly successful "fit genotypes". We have performed a longitudinal study of meningococcal carriage and disease in northern Ghana by analyzing cerebrospinal fluid samples from all suspected meningitis cases and monitoring carriage of meningococci by twice yearly colonization surveys. In the framework of this study, we observed complete replacement of an A: sequence types (ST)-2859 clone by a W: ST-2881 clone. However, after a gap of 1 year, A: ST-2859 meningococci re-emerged both as colonizer and meningitis causing agent. Our whole genome sequencing analyses compared the A population isolated prior to the W colonization and disease wave with the re-emerging A meningococci. This analysis revealed expansion of one clone differing in only one nonsynonymous SNP from several isolates already present in the original A: ST-2859 population. The colonization bottleneck caused by the competing W meningococci thus resulted in a profound reduction in genomic diversity of the A meningococcal population.

Emergence and genomic diversification of a virulent serogroup W:ST-2881(CC175) Neisseria meningitidis clone in the African meningitis belt

Countries of the African 'meningitis belt' are susceptible to meningococcal meningitis outbreaks. While in the past major epidemics have been primarily caused by serogroup A meningococci, W strains are currently responsible for most of the cases. After an epidemic in Mecca in 2000, W:ST-11 strains have caused many outbreaks worldwide. An unrelated W:ST-2881 clone was described for the first time in 2002, with the first meningitis cases caused by these bacteria reported in 2003. Here we describe results of a comparative whole-genome analysis of 74 W:ST-2881 strains isolated within the framework of two longitudinal colonization and disease studies conducted in Ghana and Burkina Faso. Genomic data indicate that the W:ST-2881 clone has emerged from Y:ST-175(CC175) bacteria by capsule switching. The circulating W:ST-2881 populations were composed of a variety of closely related but distinct genomic variants with no systematic differences between colonization and disease isolates. Two distinct and geographically clustered phylogenetic clonal variants were identified in Burkina Faso and a third in Ghana. On the basis of the presence or absence of 17 recombination fragments, the Ghanaian variant could be differentiated into five clusters. All 25 Ghanaian disease isolates clustered together with 23 out of 40 Ghanaian isolates associated with carriage within one cluster, indicating that W:ST-2881 clusters differ in virulence. More than half of the genes affected by horizontal gene transfer encoded proteins of the 'cell envelope' and the 'transport/binding protein' categories, which indicates that exchange of non-capsular antigens plays an important role in immune evasion.

The Macrolide Toxin Mycolactone Promotes Bim-Dependent Apoptosis in Buruli Ulcer through Inhibition of mTOR

Mycolactone, the macrolide exotoxin produced by Mycobacterium ulcerans, is central to the pathogenesis of the chronic necrotizing skin disease Buruli ulcer (BU). Here we show that mycolactone acts as an inhibitor of the mechanistic Target of Rapamycin (mTOR) signaling pathway by interfering with the assembly of the two distinct mTOR protein complexes mTORC1 and mTORC2, which regulate different cellular processes. Inhibition of the assembly of the rictor containing mTORC2 complex by mycolactone prevents phosphorylation of the serine/threonine protein kinase Akt. The associated inactivation of Akt leads to the dephosphorylation and activation of the Akt-targeted transcription factor FoxO3. Subsequent up-regulation of the FoxO3 target gene BCL2L11 (Bim) increases expression of the pro-apoptotic regulator Bim, driving mycolactone treated mammalian cells into apoptosis. The central role of Bim-dependent apoptosis in BU pathogenesis deduced from our experiments with cultured mammalian cells was further verified in an experimental M. ulcerans infection model. As predicted by the model, M. ulcerans infected Bim knockout mice did not develop necrotic BU lesions with large clusters of extracellular bacteria, but were able to contain the mycobacterial multiplication. Our findings provide a new coherent and comprehensive concept of BU pathogenesis.

Antibody-Mediated Neutralization of the Exotoxin Mycolactone, the Main Virulence Factor Produced by Mycobacterium ulcerans

BACKGROUND

Mycolactone, the macrolide exotoxin produced by Mycobacterium ulcerans, causes extensive tissue destruction by inducing apoptosis of host cells. In this study, we aimed at the production of antibodies that could neutralize the cytotoxic activities of mycolactone.

METHODOLOGY/PRINCIPAL FINDINGS

Using the B cell hybridoma technology, we generated a series of monoclonal antibodies with specificity for mycolactone from spleen cells of mice immunized with the protein conjugate of a truncated synthetic mycolactone derivative. L929 fibroblasts were used as a model system to investigate whether these antibodies can inhibit the biological effects of mycolactone. By measuring the metabolic activity of the fibroblasts, we found that anti-mycolactone mAbs can completely neutralize the cytotoxic activity of mycolactone.

CONCLUSIONS/SIGNIFICANCE

The toxin neutralizing capacity of anti-mycolactone mAbs supports the concept of evaluating the macrolide toxin as vaccine target.

A ring-closing metathesis (RCM)-based approach to mycolactones A/B

The total synthesis of the mycobacterial toxins mycolactones A/B (1 a/b) has been accomplished based on a strategy built around the construction of the mycolactone core through ring-closing metathesis. By employing the Grubbs second-generation catalyst, the 12-membered core macrocycle of mycolactones, with a functionalized C2 handle attached to C11, was obtained in 60-80 % yield. The C-linked upper side chain (comprising C12-C20) was completed by a highly efficient modified Suzuki coupling between C13 and C14, while the attachment of the C5-O-linked polyunsaturated acyl side chain was achieved by Yamaguchi esterification. Surprisingly, a diene containing a simple isopropyl group attached to C11 could not be induced to undergo ring-closing metathesis. By employing fluorescence microscopy and flow cytometry techniques, the synthetic mycolactones A/B (1 a/b) were demonstrated to display similar apoptosis-inducing and cytopathic effects as mycolactones A/B extracted from Mycobacterium ulcerans. In contrast, a simplified analogue with truncated upper and lower side chains was found to be inactive.

T cell receptor contact to restricting MHC molecules is a prerequisite for peripheral interclonal T cell competition

T cell survival and homeostatic proliferation in the periphery requires T cell receptor (TCR) binding to restricting major histocompatability complex (MHC)-encoded molecules, as well as the availability of certain lymphokines. However, the exact mechanisms by which these signals interrelate and contribute to homeostasis are not understood. By performing T cell transfers into TCR transgenic hosts we detected a hierarchical order of homeostatic proliferation for T cells differing in MHC restriction, such that OT1 cells (K(b) restricted) proliferated in P14 (D(b)-restricted TCR) recipients, but not vice versa. Using K(b) mutant mice, we demonstrated that proliferation of OT1 cells in P14 recipients, as well as the ability of host OT1 cells to hinder the proliferation of donor P14 cells, were dependent on OT1-TCR binding to K(b) molecules. However, interclonal T cell competition was not mediated simply by competition for physical access to the MHC-bearing cell. This was shown in parabiotic pairs of OT1 and K(b) mutant mice in which P14 cells failed to proliferate, even though the OT1 cells could not interact with half of the APCs in the system. Thus, we conclude that the interaction between the TCR and restricting MHC molecule influences the ability to compete for trophic resources not bound to the stimulating APC. This mechanism allows a local competitiveness that extends beyond a T cell's specificity.

ST2859 serogroup A meningococcal meningitis outbreak in Nouna Health District, Burkina Faso: a prospective study

We analysed cerebrospinal fluid samples from suspected meningitis cases in Nouna Health District, Burkina Faso, during the meningitis seasons of 2004-2006. Serogroup A ST2859 meningococci belonging to the ST5 clonal complex of subgroup III meningococci were the predominant causative agent. ST2859 bacteria were associated with focal outbreaks in the north of the district. While >10% of the population of an outbreak village carried ST2859, the population in the south of the district was predominantly colonised by serogroup Y ST4375 meningococci, which were associated with only sporadic cases of meningitis. Colonisation with the less virulent Y meningococci may interfere with the spread of the ST2859 to the south of the district, but there are concerns that this serogroup A clone may cause a third wave of subgroup III meningococcal disease in the African Meningitis Belt.

Improved protective efficacy of a species-specific DNA vaccine encoding mycolyl-transferase Ag85A from Mycobacterium ulcerans by homologous protein boosting

Vaccination with plasmid DNA encoding Ag85A from M. bovis BCG can partially protect C57BL/6 mice against a subsequent footpad challenge with M. ulcerans. Unfortunately, this cross-reactive protection is insufficient to completely control the infection. Although genes encoding Ag85A from M. bovis BCG (identical to genes from M. tuberculosis) and from M. ulcerans are highly conserved, minor sequence differences exist, and use of the specific gene of M. ulcerans could possibly result in a more potent vaccine. Here we report on a comparison of immunogenicity and protective efficacy in C57BL/6 mice of Ag85A from M. tuberculosis and M. ulcerans, administered as a plasmid DNA vaccine, as a recombinant protein vaccine in adjuvant or as a combined DNA prime-protein boost vaccine. All three vaccination formulations induced cross-reactive humoral and cell-mediated immune responses, although species-specific Th1 type T cell epitopes could be identified in both the NH₂-terminal region and the COOH-terminal region of the antigens. This partial species-specificity was reflected in a higher—albeit not sustained—protective efficacy of the M. ulcerans than of the M. tuberculosis vaccine, particularly when administered using the DNA prime-protein boost protocol.

Buruli ulcer (BU) is an infectious disease characterized by deep, ulcerating skin lesions, particularly on arms and legs, that are provoked by a toxin. BU is caused by a microbe belonging to the same family that also causes tuberculosis and leprosy. The disease is emerging as a serious health problem, especially in West Africa. Vaccines are considered to be the most cost-effective strategy to control and eventually eradicate an infectious disease. For the moment, however, there is no good vaccine against BU, and it is still not fully understood which immune defence mechanisms are needed to control the infection. The identification of microbial components that are involved in the immune control is an essential step in the development of an effective vaccine. In this paper, we describe the identification of one of these microbial components, i.e., antigen 85A, a protein involved in the integrity of the cell wall of the microbe. Our findings obtained in a mouse model now need to be extended to other experimental animals and later to humans. Combination with a vaccine targeting the toxin may be a way to strengthen the effectiveness of the vaccine.

Genetic diversification of Neisseria meningitidis during waves of colonization and disease in the meningitis belt of sub-Saharan Africa

Although Neisseria meningitidis is a highly variable organism, most invasive disease is caused by a minority of genotypes. Hypervirulent lineages have been identified and their pandemic spread has been traced. During a longitudinal meningococcal colonization study in a district of northern Ghana clonal waves of carriage and disease were observed. Genetic diversification of genoclouds was analysed by pulsed field gel electrophoretic (PFGE) analysis of isolates from healthy carriers and from meningitis patients. Even during the limited time of persistence in the district, microevolution of the dominating genoclouds took place. Population genomic analyses are required to understand the genetic basis for the emergence of new lineages with epidemic potential, which is of crucial importance for the development of long-term global vaccination strategies against meningococcal disease.

Clonal waves of Neisseria colonisation and disease in the African meningitis belt: eight- year longitudinal study in northern Ghana

BACKGROUND

The Kassena-Nankana District of northern Ghana lies in the African "meningitis belt" where epidemics of meningococcal meningitis have been reoccurring every eight to 12 years for the last 100 years. The dynamics of meningococcal colonisation and disease are incompletely understood, and hence we embarked on a long-term study to determine how levels of colonisation with different bacterial serogroups change over time, and how the patterns of disease relate to such changes.

METHODS AND FINDINGS

Between February 1998 and November 2005, pharyngeal carriage of Neisseria meningitidis in the Kassena-Nankana District was studied by twice-yearly colonisation surveys. Meningococcal disease was monitored throughout the eight-year study period, and patient isolates were compared to the colonisation isolates. The overall meningococcal colonisation rate of the study population was 6.0%. All culture-confirmed patient isolates and the majority of carriage isolates were associated with three sequential waves of colonisation with encapsulated (A ST5, X ST751, and A ST7) meningococci. Compared to industrialised countries, the colonising meningococcal population was less constant in genotype composition over time and was genetically less diverse during the peaks of the colonisation waves, and a smaller proportion of the isolates was nonserogroupable. We observed a broad age range in the healthy carriers, resembling that of meningitis patients during large disease epidemics.

CONCLUSIONS

The observed lack of a temporally stable and genetically diverse resident pharyngeal flora of meningococci might contribute to the susceptibility to meningococcal disease epidemics of residents in the African meningitis belt. Because capsular conjugate vaccines are known to impact meningococcal carriage, effects on herd immunity and potential serogroup replacement should be monitored following the introduction of such vaccines.

Emergence of W135 meningococcal meningitis in Ghana

Neisseria meningitidis serogroup W135, well known for a long time as a cause of isolated cases of meningococcal meningitis, has recently increasingly been associated with disease outbreaks of considerable magnitude. Burkina Faso was hit by W135 epidemics in the dry seasons of 2002-2004, but only four W135 meningitis cases were recorded between February 2003 and March 2004 in adjoining Ghana. This reconfirms previous findings that bottlenecks exist in the spreading of new epidemic N. meningitidis clones within the meningitis belt of sub-Saharan Africa. Of the four Ghanaian W135 meningitis patients one died and three survived, of whom one had profound neurosensory hearing loss and speech impairment. All four disease isolates were sensitive to penicillin G, chloramphenicol, ciprofloxacin and cefotaxime and had the multi-locus sequence type (ST) 11, which is the major ST of the ET-37 clonal complex. Pulsed-field gel electrophoresis (PFGE) profiles of the Ghanaian disease isolates and recent epidemic isolates from Burkina Faso were largely identical. We conducted meningococcal colonization surveys in the home communities of three of the patients and in the Kassena Nankana District located at the border to Burkina Faso. W135 carriage rates ranged between 0% and 17.5%. When three consecutive surveys were conducted in the patient community with the highest carrier rate, persistence of W135 colonization over a period of 1 year was observed. Differences in PFGE profiles of carrier isolates taken at different times in the same patient community were indicative of rapid microevolution of the W135 bacteria, emphasizing the need for innovative fine typing methods to reveal the relationship between W135 isolates.

An outbreak of serotype 1 Streptococcus pneumoniae meningitis in northern Ghana with features that are characteristic of Neisseria meningitidis meningitis epidemics

BACKGROUND

The Kassena-Nankana District (KND) of northern Ghana lies in the African meningitis belt, where epidemics of bacterial meningitis have been reoccurring every 8-12 years. These epidemics are generally caused by Neisseria meningitidis, an organism that is considered to be uniquely capable of causing meningitis epidemics.

METHODS

We recruited all patients with suspected meningitis in the KND between 1998 and 2003. Cerebrospinal fluid samples were collected and analyzed by standard microbiological techniques. Bacterial isolates were subjected to serotyping, multilocus sequence typing (MLST), and antibiotic-resistance testing.

RESULTS

A continual increase in the incidence of pneumococcal meningitis was observed from 2000 to 2003. This outbreak exhibited strong seasonality, a broad host age range, and clonal dominance, all of which are characteristic of meningococcal meningitis epidemics in the African meningitis belt. The case-fatality rate for pneumococcal meningitis was 44.4%; the majority of pneumococcal isolates were antibiotic sensitive and expressed the serotype 1 capsule. MLST revealed that these isolates belonged to a clonal complex dominated by sequence type (ST) 217 and its 2 single-locus variants, ST303 and ST612.

CONCLUSIONS

The S. pneumoniae ST217 clonal complex represents a hypervirulent lineage with a high propensity to cause meningitis, and our results suggest that this lineage might have the potential to cause an epidemic. Serotype 1 is not included in the currently licensed pediatric heptavalent pneumococcal vaccine. Mass vaccination with a less complex conjugate vaccine that targets hypervirulent serotypes should, therefore, be considered.

Proviral integration of an Abelson-murine leukemia virus deregulates BKLF-expression in the hypermutating pre-B cell line 18-81

The transcription factor BKLF (basic Krüppel-like factor, KLF3) is a member of the Krüppel-like factors (KLF) family. KLF members harbor a characteristic C-terminal zinc-finger DNA-binding domain and bind preferentially to CACCC-motifs. BKLF is highly expressed in haematopoietic and erythoid cells and works either as repressor or activator of transcription in various genes. BKLF-deficient mice display myeloproliferative disorders and abnormalities in haematopoiesis. Other members of the KLF-family such as GKLF and BCL11A have been implicated in tumorigenesis, however, for BKLF such association has not yet been demonstrated. We report here that a single Abelson-murine leukemia virus (A-MuLV) provirus is present in the genome of the hypermutating murine pre-B cell line 18-81. The provirus has integrated into the locus of the transcription factor BKLF. In contrast to other A-MuLV transformed pre-B cell lines, BKLF is highly transcribed in cell line 18-81. BKLF transcripts originate from the retroviral long terminal repeats (LTRs) and BKLF protein can be detected by gel shift retardation assay. We hypothesize on a potential role of BKLF deregulation in tumorigenesis and/or in the induction of somatic hypermutation in cell line 18-81.

Evidence for a stepwise evolution of the CD3 family

The three CD3 components of the TCR complex are encoded as clustered genes in mammals. The evolution of such a multimeric complex is likely to occur stepwise. The chicken CD3 cluster was entirely sequenced, and, in contrast to mammals, only two chicken CD3 genes were found to be physically linked to the unrelated genes HZW10 and epithelial V-like Ag flanking both sides of the CD3 cluster. Biochemical analyses of CD3 immunoprecipitates confirmed the presence of only two CD3 proteins and revealed an essential role for CD3gammadelta glycosylation during assembly. Functional analyses indicated that the chicken TCR/CD3 complex was efficiently down-regulated by phorbol ester treatment, demonstrating the integrity of a CD3gamma-like cytoplasmic internalization motif. These data argue for a stepwise CD3 evolution, with major differences in the TCR/CD3 structure between mammalian and nonmammalian vertebrates setting a basis for the understanding of the CD3 phylogeny and proving the ancestral nature of the CD3gammadelta protein.

Ontogeny of the immune system: gamma/delta and alpha/beta T cells migrate from thymus to the periphery in alternating waves

The embryonic thymus is colonized by the influx of hemopoietic progenitors in waves. To characterize the T cell progeny of the initial colonization waves, we used intravenous adoptive transfer of bone marrow progenitors into congenic embryos. The experiments were performed in birds because intravenous cell infusions can be performed more efficiently in avian than in mammalian embryos. Progenitor cells, which entered the vascularized thymus via interlobular venules in the capsular region and capillaries located at the corticomedullary junction, homed to the outer cortex to begin thymocyte differentiation. The kinetics of differentiation and emigration of the T cell progeny were analyzed for the first three waves of progenitors. Each progenitor wave gave rise to gamma/delta T cells 3 d earlier than alpha/beta T cells. Although the flow of T cell migration from the thymus was uninterrupted, distinct colonization and differentiation kinetics defined three successive waves of gamma/delta and alpha/beta T cells that depart sequentially the thymus en route to the periphery. Each wave of precursors rearranged all three TCR Vgamma gene families, but displayed a variable repertoire. The data indicate a complex pattern of repertoire diversification by the progeny of founder thymocyte progenitors.

HEMCAM, an adhesion molecule expressed by c-kit+ hemopoietic progenitors

We have characterized the adhesion molecule HEMCAM, which is expressed by hemopoietic progenitors of embryonic bone marrow. HEMCAM belongs to the immunoglobulin superfamily and consists of the V-V-C2-C2-C2 Ig domains. There are three mRNA splice variants. One has a short cytoplasmic tail; another has a long tail; while the third seems to lack transmembrane and cytoplasmic regions. Except for the NH2-terminal sequence, HEMCAM is identical to gicerin, a molecular involved in neurite outgrowth and Wilm's kidney tumor progression in the chicken and it is significantly homologous with MUC18 a molecule involved in melanoma progression and metastasis in human beings. In the bone marrow the HEMCAM+ cell population contains c-kit+ subsets. HEMCAM+ cells coexpressing the receptor tyrosine kinase c-kit give rise to T cells at a frequency of 0.17 when injected intrathymically in congenic animals. As HEMCAM+, c-kit+ cells differentiate into myeloid and erythroid CFU's the double-positive cell population seems to contain precursors for multiple lineages. HEMCAM promotes cell-cell adhesion of transfected cells. Cross-linking of murine HEMCAM leads to cell spreading of T-lymphocyte progenitors adhering to the vascular adhesion molecules, PECAM-1 and VCAM-1. Thus, HEMCAM is likely to be involved in cellular adhesion and homing processes.

Ontogeny of TCR V beta 1 expression revealed novel invariant alternative transcripts

Analysis of TCR-beta gene recombination and expression was performed by quantitative PCR amplification technique throughout chicken embryogenesis and development. Our data demonstrated that TCR V beta 1 promoters were turned on by day 10 of embryogenesis, 2 days before detection of TCR-beta gene recombination. The V to D recombination step was first detected by day 11 of embryogenesis whereas DJ and V(D)J rearranged genes were detected 1 day later, on day 12 of embryogenesis. Thus, transcription of unrearranged TCR-beta genes in chickens precedes the expression of V(D)J recombinase activity as in mammals. In contrast, although TCR-beta rearrangement starts with the D to J recombination step in mammals, it can start either by the VD or the DJ step in chickens. Furthermore, reverse transcriptase-PCR amplification of TCR-beta transcripts revealed the presence of two kinds of alternative transcripts. These novel alternatively spliced products appeared in thymocytes from embryonic thymus during colonization periods and were absent in transformed T cell lines. Splicing sites are located in the middle of V beta 1 segments and lead to delta V beta 1-C beta and delta V beta 1-D beta-J beta-C beta transcripts. delta V beta 1-C beta transcripts might lead to synthesis of invariant truncated TCR beta-chains containing the aminoterminal portion of the V beta 1 region followed by the C beta region. Because this type of splicing can be generated by using all known V beta 1 members, these invariant forms could play a role in thymocyte development.

Ontogeny of TCR V beta 1 expression revealed novel invariant alternative transcripts

Analysis of TCR-beta gene recombination and expression was performed by quantitative PCR amplification technique throughout chicken embryogenesis and development. Our data demonstrated that TCR V beta 1 promoters were turned on by day 10 of embryogenesis, 2 days before detection of TCR-beta gene recombination. The V to D recombination step was first detected by day 11 of embryogenesis whereas DJ and V(D)J rearranged genes were detected 1 day later, on day 12 of embryogenesis. Thus, transcription of unrearranged TCR-beta genes in chickens precedes the expression of V(D)J recombinase activity as in mammals. In contrast, although TCR-beta rearrangement starts with the D to J recombination step in mammals, it can start either by the VD or the DJ step in chickens. Furthermore, reverse transcriptase-PCR amplification of TCR-beta transcripts revealed the presence of two kinds of alternative transcripts. These novel alternatively spliced products appeared in thymocytes from embryonic thymus during colonization periods and were absent in transformed T cell lines. Splicing sites are located in the middle of V beta 1 segments and lead to delta V beta 1-C beta and delta V beta 1-D beta-J beta-C beta transcripts. delta V beta 1-C beta transcripts might lead to synthesis of invariant truncated TCR beta-chains containing the aminoterminal portion of the V beta 1 region followed by the C beta region. Because this type of splicing can be generated by using all known V beta 1 members, these invariant forms could play a role in thymocyte development.

T cell migration during development: homing is not related to TCR V beta 1 repertoire selection

T cell precursors enter the chick thymus in three waves during embryonic life. Each wave of thymocyte precursors colonizing the thymus gave rise to a similar TCR V beta repertoire in thymus, spleen and intestine both in terms of V beta 1 and J beta usage as well as in the length of V beta-D beta-J beta junctions. Seventeen V beta 1s were utilized, and a new J beta segment was found. In the progeny of the third wave, more nucleotides were deleted at the 5' end of the J beta segment, but the overall size of the CDR3 was conserved by a concomitant increase of N nucleotide addition at the V beta-D beta-J beta junctions during rearrangement. This CDR3 modification was observed in the spleen but not in the intestine, implying that progeny of the third wave migrate preferentially to the spleen, a possibility that was confirmed by adoptive cell transfers into congenic chickens. Very low frequencies of non-productive rearrangements in the intestine suggested that negative selection may occur in this organ. The present analysis indicates that V beta 1+ T cells in spleen and intestine are primarily of thymic origin, this colonization of both organs occurs in waves and is not characterized by preselection of the TCR V beta 1 repertoire.

Overexpression of c-jun, junB, or junD affects cell growth differently

The coding sequences of murine c-jun, junB, or junD, which code for proteins with practically identical dimerization and DNA binding properties, were introduced into a nondefective retroviral vector, and the phenotype of primary avian fibroblasts chronically infected with each of these viruses was studied. Cells expressing c-jun grew in low-serum medium and developed into colonies in agar, two properties characteristic of in vitro transformation. Cells expressing junB grew in agar, with a reduced efficiency as compared to c-jun, but did not grow in low-serum medium. Finally, no effect of junD expression on cell growth was observed. These different phenotypes suggest that these three closely related transcription factors play distinct roles during normal cell growth. Analysis of c-jun deletion mutants and of c-jun/junB and c-jun/junD chimeric genes showed that the N-terminal portion (amino acids 2-168) of the c-Jun protein that is involved in transcriptional activation is required for efficient transformation. On the contrary, cells expressing a truncated mouse c-Jun lacking this N-terminal domain grew slower than normal embryo fibroblasts. The reduced growth rate may be related to the finding that expression of the intact or the truncated mouse c-jun repressed the endogenous avian c-Jun homologue, suggesting that functional c-Jun product is required for normal cell growth.

Overexpression of avian or mouse c-jun in primary chick embryo fibroblasts confers a partially transformed phenotype

The coding sequences of avian (quail) or murine c-jun proto-oncogenes were introduced into a non-defective retroviral vector derived from Rous sarcoma virus (RSV) in which c-jun replaces v-src. Primary avian fibroblasts chronically infected with either one of these viruses exhibit some phenotypic traits characteristic of RSV-transformed cells, including sustained growth in low serum medium and ability to develop colonies from single cells in agar, even though they are still of normal morphology and contact inhibited. This altered growth control correlates with enhanced AP1-specific DNA binding activity as well as with higher levels of c-Jun products. Unexpectedly, repression of the endogenous c-Jun product is observed in cells overexpressing murine c-Jun. Cells expressing the avian and the murine c-Jun products display qualitatively similar phenotypes; nevertheless, for every transformed trait considered, the murine c-jun seemed more potent than its quail homologue. These data suggest that the avian or murine c-jun proto-oncogenes may trigger a subset of the 'transforming functions' normally induced by v-src, and which are more specifically related to growth in low serum and in the absence of solid support.