Abstract: A Th1 response is required for the development of Plasmodium berghei ANKA (PbA)-induced experimental cerebral malaria (ECM). The role of pro-Th1 IL-12 in malaria is complex and controversial. In this study, we addressed the role of IL-12Rβ2 in ECM development. C57BL/6 mice deficient for IL-12Rβ2, IL-12p40, or IL-12p35 were analyzed for ECM development after blood-stage PbA infection in terms of ischemia and blood flow by noninvasive magnetic resonance imaging and angiography, T cell recruitment, and gene expression. Without IL-12Rβ2, no neurologic sign of ECM developed upon PbA infection. Although wild-type mice developed distinct brain microvascular pathology, ECM-resistant, IL-12Rβ2-deficient mice showed unaltered cerebral microcirculation and the absence of ischemia after PbA infection. In contrast, mice deficient for IL-12p40 or IL-12p35 were sensitive to ECM development. The resistance of IL-12Rβ2-deficient mice to ECM correlated with reduced recruitment of activated T cells and impaired overexpression of lymphotoxin-α, TNF-α, and IFN-γ in the brain after PbA infection. Therefore, IL-12Rβ2 signaling is essential for ECM development but independent from IL-12p40 and IL-12p35. We document a novel link between IL-12Rβ2 and lymphotoxin-α, TNF-α, and IFN-γ expression, key cytokines for ECM pathogenesis.
Abstract: Platelet adhesion to the brain microvasculature has been associated with cerebral malaria (CM) in humans, suggesting that platelets play a role in the pathogenesis of this syndrome. In vitro co-cultures have shown that platelets can act as a bridge between Plasmodium falciparum-infected red blood cells (pRBC) and human brain microvascular endothelial cells (HBEC) and potentiate HBEC apoptosis. Using cDNA microarray technology, we analyzed transcriptional changes of HBEC in response to platelets in the presence or the absence of tumor necrosis factor (TNF) and pRBC, which have been reported to alter gene expression in endothelial cells. Using a rigorous statistical approach with multiple test corrections, we showed a significant effect of platelets on gene expression in HBEC. We also detected a strong effect of TNF, whereas there was no transcriptional change induced specifically by pRBC. Nevertheless, a global ANOVA and a two-way ANOVA suggested that pRBC acted in interaction with platelets and TNF to alter gene expression in HBEC. The expression of selected genes was validated by RT-qPCR. The analysis of gene functional annotation indicated that platelets induce the expression of genes involved in inflammation and apoptosis, such as genes involved in chemokine-, TREM1-, cytokine-, IL10-, TGFβ-, death-receptor-, and apoptosis-signaling. Overall, our results support the hypothesis that platelets play a pathogenic role in CM.
Abstract: Hemoglobin C (HbC) has been recently associated with protection against Plasmodium falciparum malaria. It is thought that HbC influences the development of immune responses against malaria, suggesting that the variation at the HbC locus (rs33930165) may interact with polymorphic sites in immune genes. We investigated, in 198 individuals belonging to 34 families living in Burkina Faso, statistical interactions between HbC and 11 polymorphisms within interleukin-4 (IL4), IL12B, NCR3, tumor necrosis factor (TNF) and lymphotoxin-α (LTA), which have been previously associated with malaria-related phenotypes. We searched for multilocus interactions by using the pedigree-based generalized multifactor dimensionality reduction approach. We detected 29 multilocus interactions for mild malaria, maximum parasitemia or asymptomatic parasitemia after correcting for multiple tests. All the single-nucleotide polymorphisms studied are included in several multilocus models. Nevertheless, most of the significant multilocus models included IL12B 3' untranslated region, IL12Bpro or LTA+80, suggesting that those polymorphisms play a particular role in the interactions detected. Moreover, we identified six multilocus models involving NCR3 that encodes the activating natural killer (NK) receptor NKp30, suggesting an interaction between HbC and genes involved in the activation of NK cells. More generally, our findings suggest an interaction between HbC and genes influencing the activation of effector cells for phenotypes related to mild malaria.
Abstract: The natural killer (NK) cell receptor NKp30 is involved in the recognition of tumor and dendritic cells (DCs). Here we describe the influence of three NKp30 splice variants on the prognosis of gastrointestinal sarcoma (GIST), a malignancy that expresses NKp30 ligands and that is treated with NK-stimulatory KIT tyrosine kinase inhibitors. Healthy individuals and those with GIST show distinct patterns of transcription of functionally different NKp30 isoforms. In a retrospective analysis of 80 individuals with GIST, predominant expression of the immunosuppressive NKp30c isoform (over the immunostimulatory NKp30a and NKp30b isoforms) was associated with reduced survival of subjects, decreased NKp30-dependent tumor necrosis factor-α (TNF-α) and CD107a release, and defective interferon-γ (IFN-γ) and interleukin-12 (IL-12) secretion in the NK-DC cross-talk that could be restored by blocking of IL-10. Preferential NKp30c expression resulted partly from a single-nucleotide polymorphism at position 3790 in the 3' untranslated region of the gene encoding NKp30. The genetically determined NKp30 status predicts the clinical outcomes of individuals with GIST independently from KIT mutation.
Abstract: Deciphering host responses contributing to dengue shock syndrome (DSS), the life-threatening form of acute viral dengue infections, is required to improve both the differential prognosis and the treatments provided to DSS patients, a challenge for clinicians.
Abstract: Peripheral T-cell lymphomas constitute a heterogeneous group with regard to diagnosis, treatment and prognosis. Efforts have been made to combine novel techniques with cytology and immunochemistry in order to more precisely define these entities. Molecular profiling has contributed to novel insights in the biology of T-cell lymphoma. Regarding anaplastic large cell lymphoma, low expression T-cell receptor signalling and high STAT3 target signatures have been associated with the ALK-positive subgroup. Gene expression profiling differentiates angioblastic T-cell lymphoma from other T-cell malignancies, suggests that the normal counterpart of lymphoma cells are follicular helper T cells, and supports the involvement of vascular endothelial growth factor deregulation in its physiopathology. In peripheral T-cell lymphoma unspecified, gene profiling suggests the normal counterpart of tumour cells are activated CD4(+) or CD8(+) T-lymphocytes, delineates prognostic groups depending on the proliferative signature, and suggests therapeutic options aimed at regulating nuclear factor-kappaB and platelet-derived growth factor receptor-alpha phosphorylation. Gene expression profiling of primary cutaneous T cell lymphomas highlighted the importance of abnormal methylation patterns, suggested a pivotal role for JUNB/AP-1, and defined a predictive model for response to interferon-alpha. In conclusion, gene expression profiling is beginning to change the pathological classification, the prognosis profiles and the therapeutic approach in T-cell lymphomas.
Abstract: The first scientific meeting of the newly established European SYSGENET network took place at the Helmholtz Centre for Infection Research (HZI) in Braunschweig, April 7-9, 2010. About 50 researchers working in the field of systems genetics using mouse genetic reference populations (GRP) participated in the meeting and exchanged their results, phenotyping approaches, and data analysis tools for studying systems genetics. In addition, the future of GRP resources and phenotyping in Europe was discussed.
Abstract: Tumor necrosis factor (TNF)-related genes are thought to play a role in human malaria. TNF polymorphisms have been associated with severe malaria, mild malaria, and parasitemia. Lymphotoxin-alpha gene (LTA) that belongs to the TNF family is one such candidate gene. Here we report the family-based association analysis of a cis-regulatory lymphotoxin-alpha polymorphism with parasitemia in two independent populations living in Burkina Faso. Analysis of 199 subjects (34 families) living in an urban endemic area revealed the association of the low producing LTA+80A allele with reduced parasitemia. Furthermore, there was evidence of significant LTA+80-by-age and LTA+80-by-gender interactions. In another set of 318 residents (55 families) in a rural endemic area, we found both the association of the low producing LTA+80A allele with reduced parasitemia and LTA+80-by-age and LTA+80-by-gender interactions. This study suggests that LTA+80 polymorphism influences parasitemia and acts in an age- and gender-dependent manner.
Abstract: Chromosome 5q31-q33 has been linked to Plasmodium falciparum parasitemia in several independent studies. This chromosomal region contains numerous immunoregulatory genes. Among these, IL12B that encodes the p40 subunit of interleukin-12 (IL-12) appeared to be a promising functional candidate gene, and IL12Bpro, a promoter polymorphism, was associated with mortality from severe malaria in children. In this study, we characterized genetic variation in IL12B in 215 individuals belonging to 34 families and evaluated linkage and association of parasitemia with IL12B polymorphisms and haplotypes. We searched for IL12B polymorphisms in the coding regions and the corresponding intron-exon borders. We also examined IL12Bpro and IL12B 3'untranslated region (UTR) polymorphisms, which are thought to influence the production of IL-12. We showed a high level of conservation of IL12B-coding regions and identified five polymorphisms in introns and the two polymorphisms in the promoter and the 3'UTR regions. Although IL12B polymorphisms were linked to parasitemia, there was association of parasitemia with neither polymorphisms nor haplotypes. We cannot exclude that an unknown IL12B cis-regulatory element polymorphism affects both IL-12 production and parasitemia. However, our results suggest that genetic variation in IL12B does not explain differences in parasitemia in individuals living in an endemic area.
Abstract: The identification of genes underlying complex traits is a challenging task, and there are a limited number of confirmed genes that influence human complex diseases. In particular, few genes involved in complex diseases related to immune response, such as infectious diseases and inflammatory diseases, have been identified. Recent advances in genotyping technology lead to the depository of millions of single-nucleotide polymorphisms (SNPs) into public databases, and SNPs are considered powerful tools in the search for genes involved in complex diseases. A number of SNP-genotyping methods are available, and two critical points are to select the SNPs required for a comprehensive analysis and to perform association analyses that avoid statistical biases because of population substructure. This chapter describes a way to take advantage of the mass of known SNPs and to evaluate family-based association between polymorphisms and phenotypes related to diseases, with special emphasis on innate immunity genes. After summarizing relevant aspects of genetic epidemiology, I describe how to obtain SNP data from ENSEMBL visualize an annotated sequence containing SNPs with SNPper select SNPs on the basis of population frequency and functional information explore SNP data in the IIGA database focused on innate immunity genes evaluate the association of SNPs with quantitative phenotypes by using Quantitative trait Transmission/Disequilibrium Tests (QTDT) evaluate the association of SNPs with binary and quantitative phenotypes by using Family-Based Association Tests (FBAT). All the procedures use publicly available servers and free statistical programs for academic users.
Abstract: ABSTRACT: BACKGROUND: : Microarray analyses allow the identification and assessment of molecular signatures in whole tissues undergoing pathological processes. To better understand cerebral malaria pathogenesis, we investigated intra-cerebral gene-expression profiles in well-defined genetically cerebral malaria-resistant (CM-R) and CM-susceptible (CM-S) mice, upon infection by Plasmodium berghei ANKA (PbA). We investigated mouse transcriptional responses at early and late stages of infection by use of cDNA microarrays. RESULTS: : Through a rigorous statistical approach with multiple testing corrections, we showed that PbA significantly altered brain gene expression in CM-R (BALB/c), and in CM-S (CBA/J and C57BL/6) mice, and that 327 genes discriminated between early and late infection stages, between mouse strains, and between CM-R and CM-S mice. We further identified 104, 56, 84 genes with significant differential expression between CM-R and CM-S mice on days 2, 5, and 7 respectively. The analysis of their functional annotation indicates that genes involved in metabolic energy pathways, the inflammatory response, and the neuroprotection/neurotoxicity balance play a major role in cerebral malaria pathogenesis. In addition, our data suggest that cerebral malaria and Alzheimer's disease may share some common mechanisms of pathogenesis, as illustrated by the accumulation of beta-amyloid proteins in brains of CM-S mice, but not of CM-R mice. CONCLUSION: Our microarray analysis highlighted marked changes in several molecular pathways in CM-S compared to CM-R mice, particularly at early stages of infection. This study revealed some promising areas for exploration that may both provide new insight into the knowledge of CM pathogenesis and the development of novel therapeutic strategies.
Abstract: Plasmodium falciparum malaria is a major cause of morbidity and mortality in many developing countries especially in sub-Saharan Africa. A susceptibility locus for mild malaria has been mapped to the MHC region, and TNF polymorphisms have been associated with mild malaria. The Natural Cytotoxicity-triggering Receptor 3 (NCR3) gene is located in the peak region of linkage, and is 15kb distal to TNF. In this study, we considered NCR3 as a candidate gene, and we genotyped ten NCR3 single nucleotide polymorphisms (SNPs). Here, we report evidence of an association between mild malaria and NCR3 -412G>C polymorphism located within the promoter. Population-based association analysis showed that NCR3 -412C carriers had more frequent mild malaria attacks than NCR3 -412GG individuals (P=0.001). Using the family-based association test (FBAT) program and its phenotype (PBAT) option, we further found that NCR3 -412C (P=0.0009) and a haplotype containing NCR3 -412C (P=0.008) were significantly associated with increased risk of mild malaria, and that the association was not due to the association of TNF with mild malaria. These observations suggest that there are at least two genes located on the central region of MHC involved in genetic control of human malaria. The association of NCR3 with malaria should provide new insights into the role of Natural Killer cells in this common disease.
Abstract: Tumor necrosis factor alpha (Tnf) plays a pleiotropic role in murine malaria. Some investigations have correlated Tnf with hypothermia, hyperlactatemia, hypoglycemia, and a suppression of the erythropoietic response, although others have not. In this study, we have evaluated parasitemia, survival rate and several pathological features in C57BL/6JTnf(-/-) and C57BL/6JTnf(+/+) mice after infection with Plasmodium chabaudi adami 408XZ. Compared to the C57BL/6JTnf(+/+) mice, C57BL/6JTnf(-/-) mice showed increased parasitemia and decreased survival rate, whereas blood glucose, blood lactate and body weight were not significantly different. However, C57BL/6JTnf(-/-) mice suffered significantly more from severe anemia and hypothermia than C57BL/6JTnf(+/+) mice. These results suggest that Tnf is an important mediator of parasite control, but not of anemia development. We hypothesize that the high mortality observed in the Tnf knock-out mice is due to increased anemia and pathology as a direct result of increased levels of parasitemia.
Abstract: The development of cerebral malaria (CM) in mice with Plasmodium berghei ANKA infection is under genetic control. Brain gene-expression patterns were investigated in well-defined genetically CM-resistant (CM-R; BALB/c and DBA/2) and CM-susceptible (CM-S; C57BL/6 and CBA/J) mice by use of cDNA microarrays. By combining transcriptional profiling with rigorous statistical methods and cluster analysis, we identified a set of 69 genes that perfectly discriminated between mouse strains and between CM-R and CM-S mice. The analysis of gene ontological terms revealed that the genes that clustered and were related to susceptibility to CM preferentially belonged to some biological process classes, such as those pertaining to immune responses. Using a false discovery rate of 5% and the Welch t test, we identified 31 genes with consistent differential expression between CM-R and CM-S mice. These data indicate that microarray analysis may be useful for identification of candidate genes that are potentially responsible for resistance or susceptibility to mouse CM and suggest that candidate genes identified in mice could be specifically tested in humans for an association with disease severity.
Abstract: We have previously obtained strong evidence for linkage of mild malaria attack to the MHC region, with a peak close to the tumor necrosis factor (TNF) gene. We screened, for polymorphisms, the entire TNF gene in the same sample of 34 families comprising 197 individuals living in a Plasmodium falciparum endemic area and we found 17 polymorphisms. In a longitudinal study, we investigated whether the 11 most frequent and informative polymorphisms were associated with mild malaria attack and maximum parasitemia, which was the highest parasitemia in each individual over 2 years. Mild malaria attack and maximum parasitemia were positively correlated. Transmission disequilibrium tests showed nominal evidence for association between TNF-1031, TNF-308, TNF851 and TNF1304 polymorphisms, and mild malaria attack on the one hand, and between TNF-238, TNF851 and TNF1304 polymorphisms, and maximum parasitemia on the other hand. After accounting for multiple tests, we confirmed the association of TNF-238 with maximum parasitemia and the association of TNF1304 and TNF851 with maximum parasitemia and mild malaria attack. The association tests with mild malaria attack suggest a moderate effect of TNF-308 polymorphism. In conclusion, our study suggests that several TNF variants may be part of the genetic determinants for maximum parasitemia and/or mild malaria attack.
Abstract: BACKGROUND: To extend our previous findings showing an imbalanced distribution of immunoglobulin G2 (IgG2) antibodies to Plasmodium falciparum merozoite surface protein 2 (MSP2) and a higher frequency of infection with multiple P. falciparum strains in Gabonese children with sickle cell trait (hemoglobin AS), human Fc gamma receptor (Fc gamma R) IIa (CD32) polymorphism and the rate of in vitro invasion of red blood cells (RBCs) from subjects with either hemoglobin AA or AS by multiple P. falciparum strains were investigated. METHODS: Fc gamma RIIa mutation at amino acid position 131 (arginine or histidine) was detected by polymerase chain reaction, and in vitro cultures for parasites were used to assess the invasion rate. RESULTS: Fc gamma RIIa polymorphism is normally distributed in this population, with no preferential carriage by children with hemoglobin AS. Lower levels of IgG2 subclass antibodies to MSP2 peptides were independently associated with the Fc gamma RIIa-R131 allele and with carriage of hemoglobin AS. Our data suggest that IgG3 antibody responses to MSP2 epitopes could be exacerbated by lower IgG2 levels in children with hemoglobin AS. CONCLUSIONS: The higher rate of invasion of RBCs in the presence of multiple strains may indicate that several invasion pathways are solicited simultaneously, and the longer persistence of ring forms in RBCs from the subjects with hemoglobin AS might reflect a slower multiplication phase, leading to a longer circulation and enhanced phagocytosis of these nonpathogenic parasite forms. This may contribute to the protection against P. falciparum malaria observed in children with hemoglobin AS.
Abstract: Genetic predisposition to malaria has been shown by epidemiological, case-control and linkage studies. In particular, case-control studies have recently shown association between hemoglobin C and resistance to severe malaria in Mali and to clinical malaria in Burkina Faso. In a longitudinal study of families living in an endemic area, we investigated whether hemoglobin C is associated with reduced Plasmodium falciparum parasitemia and low risk of mild malaria attack. We surveyed 256 individuals (71 parents and 185 sibs) from 53 families during 2 years. Hemoglobin C carriers had less frequent malaria attacks than AA individuals within the same age group (P=0.01). Since age correlated with malaria attack and parasitemia (P<0.0001), we took age into account in association analyses. We performed combined linkage and association analyses, which avoid biases due to population structure. Using multi-allelic tests, we evidenced association between hemoglobin genotype and phenotypes related to malarial infection and disease (P<0.001). We further analyzed individual hemoglobin alleles and detected negative association between hemoglobin C and malaria attack (P=0.00013). Analyses that took into account confounding factors confirmed the negative association of hemoglobin C with malaria attack (P=0.0074) and evidenced a negative correlation between hemoglobin C and parasitemia (P=0.0009). These associations indicate that hemoglobin C reduces parasitemia and confers protection against mild malaria attack.
Abstract: Susceptible A/J and more resistant C57BL/6J mice were infected with Plasmodium chabaudi chabaudi 54X, P.c. chabaudi AS and Plasmodium chabaudi adami 408XZ. As expected, most C57BL/6J mice survived the infections with the different isolates. But in contrast to previous observations, not all A/J mice succumbed to infection: just over 50% of A/J mice survived infections with P.c. chabaudi 54X, while 80% survived P.c. chabaudi AS. The more virulent parasite, P.c. adami 408XZ, was able to kill all A/J mice and 20% of C57BL/6J mice after an intravenous infection with 10(5) pRBC. A detailed study of four parameters of pathology (body weight, body temperature, blood glucose and RBC counts) in both mouse strains after a P.c. adami 408XZ infection showed similar patterns to those previously reported after infection with P.c. chabaudi AS. These data suggest that environmental factors as well as parasite polymorphisms might influence the severity of malaria between susceptible and resistant mice.
Abstract: A number of linkage studies in human populations have identified a locus ( pfbi) on Chromosome 5q31-q33 controlling Plasmodiun falciparum blood infection levels. This region contains numerous candidate genes encoding immunological molecules such as cytokines, growth factors and growth-factor receptors. We have used an F(11) advance intercross line (AIL) population of mice infected with Plasmodium chabaudi to identify additional mouse quantitative trait loci (QTL) for control of parasitaemia on Chrs 11 and 18, which carry regions homologous to human Chr 5q31-q33. Herein, we report a novel QTL for parasitaemia control ( char8) on the mouse Chr 11, linked to marker D11Mit242, and involved in the clearance stages of the parasites from the bloodstream. Strikingly, several Th2 cytokines that are located within char8 have been identified to play a predominant role in the late stages of the infection.
Abstract: We developed an F(11) AIL population from an F(1) cross of A/J (susceptible) and C57BL/6J (resistant) mouse strains. One thousand F(11) mice were challenged with P.c. chabaudi 54X, and 340 mice selected from the phenotypic extremes for susceptibility and resistance were genotyped for microsatellite markers on Chromosomes (Chrs) 5, 8, and 17. QTL originally detected in backcross and F(2) populations were confirmed on the three chromosomes within narrower genomic regions, by maximum likelihood and regression analyses. Each of the previously mapped QTL on Chrs 5 and 17 resolved into two linked QTLs. The distal and proximal QTLs on Chrs 5 and 17, respectively, map to the previously reported QTL.
Abstract: We have previously mapped a locus controlling Plasmodium falciparum blood infection levels (PFBI) to chromosome 5q31-q33. We genotyped 19 microsatellite markers on chromosome 5q31-q33 in a new sample of 44 pedigrees comprising 84 nuclear families and 292 individuals living in a P. falciparum endemic area. Using a nonparametric multipoint variance-component approach (by GENEHUNTER), we evidenced a peak of linkage close to D5S636 (P=0.0069), with a heritability of 0.46. Using a variance-component method for linkage-disequilibrium mapping of quantitative traits (by QTDT) and the Bonferroni correction for multiple testing, we further detected allelic association in the presence of linkage between blood infection levels and D5S487 (P=6 x 10(-5); P(c)=0.0011), which is located on the distal part of the peak. These results confirm the importance of chromosome 5q31-q33 in the genetic control of PFBI levels.
Abstract: Tumor necrosis factor alpha (TNF alpha) is thought to be a critical mediator of malaria fever, and mild malaria was previously reported to be linked to the MHC region containing the tumor necrosis factor alpha gene (TNF). Thirty-four families from Burkina Faso were analyzed to test for linkage between polymorphisms within the MHC region and mild malaria using the maximum-likelihood-binomial (MLB) program. Two-point analysis indicated linkage of mild malaria to TNFd (LOD = 3.27; P = 5.44 x 10(-5)). Using multipoint analysis, we also found evidence for linkage of mild malaria to the MHC region, with a peak close to TNF (LOD = 3.86; P = 1.22 x 10(-5)). Our results support genes within the MHC region being involved in mild malaria. In particular, the genetic variation within TNF may influence susceptibility to mild malaria. Nevertheless, TNF-238, TNF-244 and TNF-308 polymorphisms are unlikely to explain linkage of mild malaria to the MHC region, and the causal mutations remain to be identified.
Abstract: Host genes are thought to determine the immune response to malaria infection and the outcome. Cytophilic antibodies have been associated with protection, whereas noncytophilic antibodies against the same epitopes may block the protective activity of the protective ones. To assess the contribution of genetic factors to immunoglobulin G (IgG) subclass responses against conserved epitopes and Plasmodium falciparum blood-stage extracts, we analyzed the isotypic distribution of the IgG responses in 366 individuals living in two differently exposed areas in Burkina Faso. We used one-way analysis of variance and pairwise estimators to calculate sib-sib and parent-offspring correlation coefficients, respectively. Familial patterns of inheritance of IgG subclass responses to defined antigens and P. falciparum extracts appear to be similar in the two areas. We observed a sibling correlation for the IgG, IgG1, IgG2, IgG3, and IgG4 responses directed against ring-infected-erythrocyte surface antigen, merozoite surface protein 1 (MSP-1), MSP-2, and P. falciparum extract. Moreover, a parent-offspring correlation was found for several IgG subclass responses, including the IgG, IgG1, IgG2, IgG3, and IgG4 responses directed against conserved MSP-2 epitopes. Our results indicated that the IgG subclass responses against P. falciparum blood-stage antigens are partly influenced by host genetic factors. The localization and identification of these genes may have implications for immunoepidemiology and vaccine development.
Abstract: Natural killer (NK) cells are components of the innate immune system that can recognize and kill virally infected cells, tumor cells, and allogeneic cells without prior sensitization. NK cells also elaborate cytokines (e.g., interferon-gamma and tumor necrosis factor-alpha) and chemokines (e.g., macrophage inflammatory protein-1alpha) that promote the acquisition of antigen-specific immunity. NK cell differentiation is accompanied by the cell surface expression of a mucin-like glycoprotein bearing an NK cell-restricted keratan sulfate-related lactosamine carbohydrate, the PEN5 epitope. Here, we report that PEN5 is a post-translational modification of P-selectin glycoprotein ligand-1 (PSGL-1). The PEN5 epitope creates on PSGL-1 a unique binding site for L-selectin, which is independent of PSGL-1 tyrosine sulfation. On the surface of NK cells, the expression of PEN5 is coordinated with the disappearance of L-selectin and the up-regulation of Killer cell Ig-like Receptors (KIR). These results indicate that NK cell differentiation is accompanied by the acquisition of a unique carbohydrate, PEN5, that can serve as part of a combination code to deliver KIR(+) NK cells to specific tissues.
Abstract: There is accumulating evidence for a role of immunoglobulin G (IgG) in protection against malarial infection and disease. Only IgG1 and IgG3 are considered cytophilic and protective against P. falciparum, whereas IgG2 and IgG4 were thought to be neither and even to block protective mechanisms. However, no clear pattern of association between isotypes and protection has so far emerged. We analyzed the isotypic distribution of the IgG response to conserved epitopes and P. falciparum blood-stage extract in 283 malaria-exposed individuals whose occurrence of infection and malaria attack had been monitored for about 1 year. Logistic regression analyses showed that, at the end of the season of transmission, high levels of IgG2 to RESA and to MSP2 epitopes were associated with low risk of infection. Indeed, IgG2 is able to bind FcgammaRIIA in individuals possessing the H131 allele, and we showed that 70% of the study subjects had this allele. Also, high specific IgG4 levels were associated with an enhanced risk of infection and with a high risk of malaria attack. Moreover, specific IgG2 and IgG3 levels, as well as the IgG2/IgG4 and IgG3/IgG4 ratios, increased with the age of subjects, in parallel with the protection against infection and disease. IgG4 likely competes with cytophilic antibodies for antigen recognition and may therefore block cytotoxicity mediated by antibody-activated effector cells. In conclusion, these results favor a protective role of IgG3 and IgG2, which may activate effector cells through FcgammaRIIA, and provide evidence for a blocking role of IgG4 in malarial infection and disease.
Abstract: Genetic factors have clearly been shown to play a role in controlling malarial infection in animal models. There is now also increasing evidence for the genetic control of malaria in man. We carried out a segregation analysis based on blood parasite load phenotype for a population of the town of Bobo-Dioulasso (Burkina-Faso). This analysis demonstrated a strong genetic effect. Our results were not consistent with the segregation of a major gene and thus suggest that parasite load is under the control of minor genes. The genetic effect was stronger in children than in adults. We carried out a regression analysis in children and found that there was an association between the phenotype for blood parasite load and the q31-33 region of chromosome 5. We identified a gene in this region, Pfil1 (Plasmodium falciparum infection levels 1), which accounted for almost 50% of the variance in blood parasite load and which played a fundamental role in the control of infection. The 5q31-33 region contains several genes encoding cytokines that regulate T lymphocytes. The identification of genes controlling malarial infection opens up new possibilities for preventive and treatment strategies. It should be possible in the near future to identify individuals at risk of malaria, who would derive the greatest benefit from preventive and therapeutic measures. Finally, a deeper understanding of these genes controlling protective immune responses could be of value for the development of vaccines.
Notes: 1157-5999 (Print) xD;Comparative Study xD;English Abstract xD;Journal Article
Abstract: There is accumulating evidence of host genetic control in malaria infection and, in humans, some genes have been associated with severe malaria. Nevertheless, other important genes controlling blood infection levels, malarial disease and immune responses are likely to be identified. In this paper, we focus on segregation and linkage analyses of blood infection levels in an urban population living in Burkina Faso. We found evidence of a complex genetic control and a linkage to chromosome 5q31-q33. The identification of genes controlling complex traits related to malaria infection should be helpful in understanding protective mechanisms and the relationship between infection, malaria attacks and severe malaria.
Abstract: The genetic control of blood infection levels in human malaria remains unclear. Case control studies have not demonstrated a strong association between candidate genes and blood parasite densities as opposed to surveys that have focused on severe malaria. As an alternative approach, we used segregation analyses to determine the genetic control of blood parasitemia. We surveyed 509 residents (53 pedigrees) in a rural area and 389 residents (41 pedigrees) in an urban area during 18 months. Each family was visited 20 times and 28 times in the urban area and in the rural area; the mean number of parasitemia measurements per subject was 12.1 in the town and 14.9 in the village. The intensity of transmission of Plasmodium falciparum was 8-fold higher in the rural area than in the urban area. Using the class D regressive model for both populations, we found that blood parasite densities were correlated between sibs. We obtained strong evidence for a major effect, but we found that the transmission of this major effect was not compatible with a simple Mendelian model, suggesting a more complex mode of inheritance. Moreover, there was a strong interaction between major effect and age, suggesting that the influence of the putative major gene may be more prominent in children than in adults. Further nonparametric linkage studies, such as sib pair analysis, that focus on children would help us better understand the genetic control of blood infection levels.
Abstract: Plasmodium falciparum malaria remains a major cause of morbidity and mortality in many tropical countries, especially those in sub-Saharan Africa. Human genetic control of malaria infection is poorly understood; in particular, genes controlling P. falciparum blood infection levels remain to be identified. We recently evidenced the existence of complex genetic factors controlling blood infection levels in an urban population living in Burkina Faso. We performed, on 153 sibs from 34 families, sib-pair linkage analyses between blood infection levels and chromosome 5q31-q33, which contains numerous candidate genes encoding immunological molecules. Our results, obtained by means of the two-point Haseman-Elston (HE) method and a nonparametric (NP) approach, show linkage of parasitemia to D5S393 (P=.002) and D5S658 (P=.0004). Multipoint analyses confirmed linkage, with a peak close to D5S658 (P=.0013 and P=.0007 with the HE and NP methods, respectively). The heritability of the locus was .48, according to the two-point results, and .43, according to the multipoint results; this indicates that its variation accounted for approximately 45% of the variance of blood infection levels and that the locus plays a central role in the control of parasitemia. The identification of the gene is, therefore, of major interest in understanding the mechanisms controlling P. falciparum parasitemia.
Abstract: The hypothesis of an association between human resistance to reinfection by the parasite Schistosoma mansoni and anti-larval immunoglobulin isotypes was tested by logistic regression in the presence of the explicative variables water contact, age, and sex. Of the seven isotypes tested (IgM, IgG1, IgG2, IgG3, IgG4, IgA, and IgE), only IgE, IgG4, and IgG2 showed an association (positive for IgE and negative for IgG2 and IgG4) with resistance to reinfection after chemotherapy. The opposite effects of IgE and IgG4 were undissociable in the analysis, indicating that these isotypes probably antagonize each other in protection. The negative association of IgG2 with resistance is consistent with the view that anti-carbohydrate antibodies may facilitate reinfection. Finally, epidemiologic and immunologic studies support the view that there is a progressive but slow development of acquired immunity in children and adolescents.
Abstract: A method allowing the immunopurification of human IgE from small volumes of sera with a yield close to 100% (mean = 97.8%; SEM = 0.7) has been developed. The immunopurification eluates were cleared of other class antibodies that could compete with IgE in specific assays. Immunopurification of IgE followed by specific IgE enzyme-linked immunosorbent assay (ELISA) (IMMEL) was then applied to sera of 160 individuals from an area endemic for Schistosoma mansoni. In comparison with radioimmunosorbent test (RAST) and ELISA performed on unfractionated sera, IMMEL provided the highest specific IgE signals. Furthermore, the best correlations between the specific IgE levels and either the specific basophil histamine release levels (r = 0.84; p less than 10(-4) or the anti-S. mansoni skin test values (r = 0.45; p = 10(-4)) were obtained with IMMEL. Measurement of anti-S. mansoni IgE levels in immunopurified fractions and in unfractionated sera of these 160 individuals revealed a strong serum inhibition (geometric means of 98.6% and 96.8% for the adult worms and the larvae, respectively) of the specific IgE reactivity in ELISA. This inhibition was correlated with the anti-adult worm and anti-larval IgG4 levels (r = 0.65; p less than 10(-4) and r = 0.58; p less than 10(-4), respectively). In contrast, this inhibition did not correlate with the specific IgG1, IgG2, IgG3 and IgM levels. Furthermore, the level of specific IgG4 was clearly lower than that of specific IgG1, suggesting that the major contribution of IgG4 in the competition effect is not due to higher levels but rather to a specificity spectrum close to that of the specific IgE. These results support the idea that a specific function of IgG4 in serum might be to control antigen recognition by IgE and consequently, to regulate anaphylactic reactions and IgE-mediated immunity.
Abstract: The design of programs for the control of endemies requires the knowledge of the principal factors that determine parasite transmission and infection levels in exposed populations. In the studies summarized in this article, the role of environmental and host specific factors in the infection by S. mansoni have been evaluated. It is shown that a limited number of factors actually influences infection intensity: water contacts, age, and sex were shown to account for 20 to 25% of infection variance, while 35 to 40% of it was accounted for by the effect of a major codominant gene. A remarkable fact is the important weighting (around 55% of the variance) of factors (the major gene and age) that influence human capacities of resistance. This observation strongly supports control measures aimed at increasing human resistance, such as vaccination. The effect of age on the development of resistance has now been observed in several studies on S. mansoni or S. haematobium. It is, therefore, a constant finding in schistosomiasis infections that resistance develops extremely slowly requiring a long period of exposure to the parasite and repeated infections. These studies provide strong incentives to increase efforts in the evaluation of the immune response of subjects living in endemic areas. Such evaluations are necessary to define vaccine and vaccination programs, and they are also urgently needed to evaluate the effects of chemotherapy on the development of immunity in children and adolescents, as well as on the persistence of protective immunity in adults. Immunological studies begin to provide a clearer picture of the role of acquired immunity in human protection against S. mansoni. It is increasingly clear that the slow development of resistance in children, as well as its alteration in certain age groups, are related to the maturation of parasite specific immunity and its alteration by specific immune factors. Thus, the development of resistance is associated with the maturation of IgE-dependent immunity, whereas blocking Ab may interfere in children and adolescents with the expression of full resistance. This finding raises the question as to whether a vaccine could include major allergens without triggering the well-known deleterious side effects associated with hypersensitivity reactions. The absence of such reactions in subjects with high parasite-specific IgE levels who are exposed to daily infections suggests that this may be feasible.
Abstract: The anti-larval IgE antibody response of adolescents with high or low resistance to infection by Schistosoma mansoni was evaluated before parasitological cure with oxamniquine and over an extended post-treatment period during which the least resistant subjects regained high infections. IgE from most sera, taken at several bleeding times before and after treatment, reacted, on immunoblots, with a large number of antigens (Ag) in schistosomular tegument extract. A family of 120-165-kDa cross-reacting molecules and a 85-kDa Ag were the most prominent Ag. Some of these determinants were shown to be located on the outer tegumental membrane and to be accessible to IgE on living larvae. The comparison of IgE between the two study groups showed that IgE levels were on average six-to eightfold higher (p less than 0.01) in the sera of the most resistant adolescents whereas there was no difference in patterns of Ag recognition between study groups. In contrast to IgE, anti-larval IgG and IgM levels were either similar in both groups or higher in the least resistant subjects when these exhibited high reinfection levels. IgG that competed for the binding of IgE to larval Ag were detected in most sera and their levels were higher in the least resistant group after reinfection. Finally, the treatment had no observable long-lasting effects on the levels and on the specificity of the anti-larval IgE. Altogether, these observations can be taken as evidence supporting a role of IgE in human resistance to infection by S. mansoni.
