387 research outputs found
Sub-grouping of <it>Plasmodium falciparum </it>3D7 <it>var </it>genes based on sequence analysis of coding and non-coding regions
No full textAbstract Background The variant surface antigen family Plasmodium falciparum erythrocyte membrane protein-1 (PfEMP1) is an important target for protective immunity and is implicated in the pathology of malaria through its ability to adhere to host endothelial receptors. The sequence diversity and organization of the 3D7 PfEMP1 repertoire was investigated on the basis of the complete genome sequence. Methods Using two tree-building methods we analysed the coding and non-coding sequences of 3D7 var and rif genes as well as var genes of other parasite strains. Results var genes can be sub-grouped into three major groups (group A, B and C) and two intermediate groups B/A and B/C representing transitions between the three major groups. The best defined var group, group A, comprises telomeric genes transcribed towards the telomere encoding PfEMP1s with complex domain structures different from the 4-domain type dominant of groups B and C. Two sequences belonging to the var1 and var2 subfamilies formed independent groups. A rif subgroup transcribed towards the centromere was found neighbouring var genes of group A such that the rif and var 5' regions merged. This organization appeared to be unique for the group A var genes Conclusion The grouping of var genes implies that var gene recombination preferentially occurs within var gene groups and it is speculated that the groups reflect a functional diversification evolved to cope with the varying conditions of transmission and host immune response met by the parasite.</p
Cytophilic Antibodies to Plasmodium Falciparum Glutamate Rich Protein are Associated with Malaria Protection in an Area of Holoendemic Transmission.
No full textSeveral studies conducted in areas of medium or low malaria transmission intensity have found associations between malaria immunity and plasma antibody levels to glutamate rich protein (GLURP). This study was conducted to analyse if a similar relationship could be documented in an area of intense malaria transmission. A six month longitudinal study was conducted in an area of holoendemic malaria transmission in north-eastern Tanzania, where the incidence of febrile malaria decreased sharply by the age of three years, and anaemia constituted a significant part of the malaria disease burden. Plasma antibodies to glutamate rich protein (GLURP) were analysed and related with protection against malaria morbidity in models correcting for the effect of age. The risk of febrile malaria episodes was reduced significantly in children with measurable anti-GLURP IgG1 antibodies at enrollment [adjusted odds ratio: 0.39 (95% CI: 0.15, 0.99); P = 0.047]. Interestingly, there was an inverse relationship between the plasma anti-GLURP IgG1 and IgG3 levels and the levels of parasitaemia at enrollment. However, anti-GLURP IgG2 and IgG4 levels were not associated with reduction in parasite density. Similarly, antibody levels were not associated with haemoglobin levels or anaemia risk. Cytophilic IgG1 and IgG3 antibodies against R0-GLURP may contribute to the control of parasite multiplication and reduction in febrile malaria incidence in children living in an area of intense malaria transmission
Antigen-specific influence of GM/KM allotypes on IgG isotypes and association of GM allotypes with susceptibility to <it>Plasmodium falciparum </it>malaria
No full textAbstract Background Plasmodium falciparum malaria is a complex disease in which genetic and environmental factors influence susceptibility. IgG isotypes are in part genetically controlled, and GM/KM allotypes are believed to be involved in this control. Methods In this study, 216 individuals from Daraweesh, an area of seasonal malaria transmission in Sudan, were followed for nine years for malaria infection. Total IgG and IgG isotypes against four malaria antigens, MSP2-3D7, MSP2-FC27, AMA1, and Pf332-C231 were measured in plasma obtained from the cohort at the end of the study, during the dry malaria-free period. The GM/KM allotypes of the donors were determined. Results The GM 1,17 5,13,14,6 phenotype was associated with a higher incidence of malaria compared with the non-1,17 5,13,14,6 phenotypes (P = 0.037). Paradoxically, the carriers of the GM 1,17 5,13,14,6 phenotype had significantly higher baseline levels of total IgG and non-cytophilic IgG isotypes as compared to non-carriers. The KM allotypes influence on IgG isotypes level was limited. Finally, the differences in the baseline concentrations of total IgG and IgG isotypes between the different GK/KM phenotype carriers were antigen-dependent. Discussion The results show that GM but not KM allotypes appeared to influence host susceptibility to uncomplicated malaria as well as the antibody profile of the donors, and the carriers of the GM 1,17 5,13,14,6 phenotype were the most susceptible Conclusions The GM allotypes have significant influence on susceptibility to uncomplicated P. falciparum malaria and antigen-dependent influence on total IgG and IgG subclasses.</p
Developing Plasmodium falciparum malaria vaccines for populations living in areas with stable parasite transmission
No full textIndividuals living in areas with stable transmission of Plasmodium falciparum parasites develop substantial protective immunity to the disease during childhood. Because of naturally acquired immunity, which appears mainly to target parasite-encoded Variable Surface Antigens (VSA) on the Infected Erythrocytes (IE), severe and life-threatening disease among adults in such areas is rare. However, low-grade asymptomatic parasitaemia continues to be present in a large proportion of people. So far, experimental P. falciparum malaria vaccination employing non-VSA antigens have resulted in variable degrees of protection, including sterile protection, but the duration of the protection afforded is short-lived, probably due to insufficient boosting. Based on these findings, our approach to vaccine development is to accelerate naturally acquired VSA-specific immunity. The ambition is to develop vaccines that will protect against mortality and severe morbidity, but which allow persistence of low-grade, asymptomatic infection. Hopefully, this approach will ensure regular boosting of immunity that appears necessary for the long-lasting protection required of vaccines to be deployed in
malaria-endemic areas
Prospects and challenges regarding Plasmodium falciparum erythrocyte membrane protein I as vaccine antigens
No full textUdgivelsesdato: 2008/
Pathology of post-kala-azar dermal leishmaniasis: a light microscopical, immunohistochemical, and ultrastructural study of skin lesions and draining lymph nodes
No full textUdgivelsesdato: 2006-DecBACKGROUND: Whereas the clinical manifestations and treatment of post-kala-azar dermal leishmaniasis (PKDL) have been adequately described before, the pathology received little attention, particularly the African form of PKDL which shows some clinical differences from the disease in India. Therefore, our aim was to characterize the pathology and the immunohistopathology in PKDL lesions and correlate the histopathological findings with the clinical features of the disease. METHODS: Biopsies of skin lesions were examined for histopathological changes in formalin-fixed tissues and for cell phenotypes and adhesion molecules by immunohistochemistry. RESULTS: The epidermis showed various changes in different combinations. The dermis was infiltrated by lymphocytes and macrophages, but plasma cells were scanty or absent. The majority of cells were CD3 T cells, with a preponderance of CD4 over CD8 cells. Degenerating basal keratinocytes expressed HLA-DR, ICAM-1 and Leishmania antigen and closely interacted with CD4 T cells. Regional lymph nodes showed hyperplasia of the B- and T-cell zones. Conclusions: The inflammatory reaction in PKDL lesions is in response to Leishmania parasites and/or antigen. The majority of cells are CD4 T cells. Degeneration of the basal keratinocytes is probably due to the action of cytotoxic CD4 T cells interacting with leishmania-expressing epidermal cells. Ismail A, Gadir AFA, Theander TG, Kharazmi A, El Hassan AM. Pathology of post-kala-azar dermal leishmaniasis: a light microscopical, immunohistochemical, and ultrastructural study of skin lesions and draining lymph nodes
Seasonal changes in human immune responses to malaria
No full textUdgivelsesdato: 1993-JanCellular as well as humorol immune responses to malaria antigens fluctuate in time in individuals living in molono-endemic areas, particularly where malaria transmission is seasonal. The most pronounced changes are seen in association with clinical attacks, but osymptomatic infection can also lead to apparent immune depression. However, recent data have shown that seasonal variation in cellular immune responses may occur even in the absence of detectable porositaemia. Here, Lars Hviid and Thor G. Theonder review the seasonal variation in human immune responses to malaria, and discuss its possible causes and implications
Regulatory immune responses in humans naturally primed to Plasmodium falciparum or vaccinated with tetanum toxoid or purified protein derivative
No full textIt is well established that the balance between functionally distinct regulatory CD4+ T cells plays a major role in the development of immunity and/or pathogenesis to many different infections. In spite of the importance of Th lineage commitment in disease, the critical questions how the balance between Th1 and Th2 cells is regulated is largely unresolved. This thesis describes work aimed at assessing CD4+ T cell heterogeneity and how this is regulated in humans naturally primed to P. falciparum malaria or vaccinated with tetanus toxoid or BCG.Different types of antigens have been implicated to be of importance in the polarization of Th1 or Th2 cells. To investigate this, we stimulated peripheral blood mononuclear cells (PBMC) with tetanus toxoid (TT) and the mycobacterial antigen, purified protein derivative (PPD) in vitro and determined the number of IFN-g (Th1 cytokine) and IL-4 (Th2 cytokine) producing cells using the ELISPOT assay. PPD preferentially induced IFN-g and very few IL-4 producing cells, while TT- induced both IL-4 and IFN-g. These differences probably reflect the different types of immune responses the two antigens induce, mycobacteria preferentially a cell-mediated Th1 type of immunity, while immunity to tetanus is an antibody-dependent, Th2 type of response.To investigate the role of Th1 and Th2 cells in the regulation of anti-malarial IgE in individuals living in P.falciparum endemic areas, the number of IL-4 and IFN-g producing cells was correlated to the plasma anti-malarial IgE levels. A negative correlation between the number of IFN-g producing cells and anti-P.falciparum IgE was found. For IL-4 there was a weak positive correlation with anti-malarial IgE levels, suggesting that other cells than T cells can produce IL-4. The anti-malarial IgE levels correlated significantly with an increased ratio of IL-4/IFN-g producing cells. These data suggest a regulatory role for IL-4 in the induction of anti-P.falciparum IgE antibodies.When PBMC from two groups of individuals naturally exposed to P.falciparum, living in two different parts of Africa (Burkina Faso and Tanzania), were stimulated in vitro with P.falciparum antigens, no malaria-specific IL-4 producing cells were detected. The levels of IgE were lower in the Burkina individuals as compared to the Tanzania ones. This might reflect differences in malaria exposure or genetic (ethnic) differences between the two study groups.To study the influence of genetic and/or environmental factors on the development and shaping of the human peripheral T cell repertoire, the T cell receptor (TCR) Vb usage in ten adult monozygous (Mz) and nine dizygous (Dz) twin pairs living in a P.falciparum endemic area in The Gambia was studied. The results revealed that the frequencies of cells expressing particular TCR Vb genes were not influenced by the parasitaemia, indicating that malaria exposure is not a dominating factor in shaping the peripheral TCR repertoire in humans. The mean within-pair difference was significantly lower for the Mz than for the Dz pairs. The mean within-pair difference for a group of MHC-class II identical twin pairs was significantly higher than for the Mz group but similar to that of the Dz as a whole. These data indicate that genetic factors other than MHC class II genes (i.e non-MHC) influence the shaping of the peripheral TCR Vb repertoire in humans.To study whether or not IgE-containing malaria sera have the capacity to induce IL-4 in human basophils, IgE containing sera from malaria immune donors were added to tissue culture plates coated with anti-human IgE antibodies. IgE-anti-IgE complexes induced IL-4 in basophils. Serum depleted of IgE induced significantly less IL-4. These data show that malaria IgE can induce IL-4 production in cells of basophil origin that can subsequently amplify Th2 type of responses.Taken together, our data show the existence of functionally distinct T cells in individuals naturally primed to P.falciparum or vaccinated with TT or BCG.</p
IgG responses to Anopheles gambiae salivary antigen gSG6 detect variation in exposure to malaria vectors and disease risk.
No full textAssessment of exposure to malaria vectors is important to our understanding of spatial and temporal variations in disease transmission and facilitates the targeting and evaluation of control efforts. Recently, an immunogenic Anopheles gambiae salivary protein (gSG6) was identified and proposed as the basis of an immuno-assay determining exposure to Afrotropical malaria vectors. In the present study, IgG responses to gSG6 and 6 malaria antigens (CSP, AMA-1, MSP-1, MSP-3, GLURP R1, and GLURP R2) were compared to Anopheles exposure and malaria incidence in a cohort of children from Korogwe district, Tanzania, an area of moderate and heterogeneous malaria transmission. Anti-gSG6 responses above the threshold for seropositivity were detected in 15% (96/636) of the children, and were positively associated with geographical variations in Anopheles exposure (OR 1.25, CI 1.01-1.54, p = 0.04). Additionally, IgG responses to gSG6 in individual children showed a strong positive association with household level mosquito exposure. IgG levels for all antigens except AMA-1 were associated with the frequency of malaria episodes following sampling. gSG6 seropositivity was strongly positively associated with subsequent malaria incidence (test for trend p = 0.004), comparable to malaria antigens MSP-1 and GLURP R2. Our results show that the gSG6 assay is sensitive to micro-epidemiological variations in exposure to Anopheles mosquitoes, and provides a correlate of malaria risk that is unrelated to immune protection. While the technique requires further evaluation in a range of malaria endemic settings, our findings suggest that the gSG6 assay may have a role in the evaluation and planning of targeted and preventative anti-malaria interventions
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