Wormy mothers, healthy babies: case closed or conundrum?

Host-parasite interactio

Persistent Epstein-Barr viral reactivation in young African children with a history of severe Plasmodium falciparum malaria.

Item does not contain fulltextEpstein-Barr virus (EBV) and Plasmodium falciparum have overlapping distributions and are thought to have causal interactions, particularly with regard to the aetiology of endemic Burkitt's lymphoma. Using real-time PCR, we quantified and compared EBV DNA levels in the blood before and after antimalarial treatment of age- and gender-matched groups of Gabonese children who presented with either mild or severe P. falciparum malaria. Following treatment, the prevalence of EBV DNA declined in the mild malaria group but increased in the severe malaria group, and a significantly higher proportion of the latter had EBV DNA detectable in their blood when they were healthy and parasite free (67% vs. 39%; P=0.013). High EBV DNA loads were associated with more malaria attacks and with elevated plasma concentrations of both TNF-alpha and IL-12p40. Significantly more under 5 year olds had EBV DNA, highlighting the strong age dependence of the interaction between the two pathogens. These findings confirm that EBV is reactivated during acute P. falciparum malaria but, importantly, also reveal that: (i) EBV activity persists at a higher frequency in children with a history of severe malaria; and (ii) higher peripheral blood EBV DNA loads are associated with susceptibility to more frequent P. falciparum episodes and with altered cytokine activity

Activation status of cord blood gamma delta T cells reflects in utero exposure to Plasmodium falciparum antigen.

Item does not contain fulltextBACKGROUND: Placental Plasmodium falciparum infection modulates neonatal cell-mediated immune responses and is associated with increased susceptibility of infants to malaria. METHODS: By flow-cytometric analysis of maternal peripheral and cord blood samples collected at delivery, we measured and compared the activation status and proinflammatory cytokine activity of T cells from women segregated into groups according to malaria status. RESULTS: Stimulation with phorbol myristate acetate/ionomycin resulted in the highest percentages of tumor necrosis factor-alpha- and interferon-gamma-positive gamma delta T cells in peripheral blood samples and in corresponding cord blood samples from those treated for malaria during pregnancy. Cord blood samples from this group also contained significantly higher percentages of CD69(+) and CD25(+) gamma delta T cells and CD3(+) T cells, compared with samples from either the group with active placental P. falciparum infection at delivery or the group with no infection. Proinflammatory cytokine activity of cells from the group with placental P. falciparum infection at delivery was either similar to or lower than that of cells from the group with no infection. CONCLUSIONS: The findings imply that treatment of P. falciparum malaria during pregnancy leads to enhanced innate immune T cell activation and proinflammatory cytokine responses in both maternal and fetal compartments. Ongoing placental P. falciparum infection, conversely, is associated with an absence of such activity

Placental Plasmodium falciparum infection: causes and consequences of in utero sensitization to parasite antigens.

Contains fulltext : 51932.pdf (publisher's version ) (Closed access)Available evidence suggests that, in African populations, systemic blood-dwelling parasitoses of mothers are associated with enhanced susceptibility to infection of their offspring. Thus, children born to mothers with filariasis or schistosomiasis are infected earlier, and offspring of mothers with placental Plasmodium falciparum at delivery, commonly referred to as pregnancy-associated malaria or PAM, are themselves at higher risk of developing parasitaemia during infancy. Since foetal/neonatal antigen-presenting cells (APC) are either immature or provide insufficient costimulatory signals to T cells, thus favouring tolerance induction, it is commonly assumed that soluble parasite components [protein antigens], transferred transplacentally and inducing foetal immune tolerance, are largely, if not exclusively, responsible for these outcomes. Plasmodial asexual blood stage antigen-specific T cells are detectable in as many as two-thirds of all cord blood samples in malaria-endemic countries of sub-Saharan Africa, indicating that in utero sensitization may be a common phenomenon during pregnancy in these populations. Parasite antigen-specific T cell responses of neonates born to helminth-infected mothers display a highly skewed Th2-type cytokine pattern, with a prominent role for the regulatory cytokine interleukin (IL)-10. Similarly, the cord blood immune response of those born to mothers identified with on-going PAM is characterised by inducible parasite antigen-specific IL-10-producing regulatory T cells that can inhibit both APC HLA expression and Th1-type T cell responses. In contrast, plasmodial antigen-specific Th1-type responses, characterised by IFN-gamma production, predominate in cord blood of those born to mothers successfully treated for Pf malaria during gestation, suggesting that the duration and/or the nature of antigen exposure in utero governs the outcome with respect to neonatal immune responses. Aspects of APC function in the context of these differentially modulated responses, whether and how the latter translate into altered susceptibility to Pf infection during infancy, as well as the possible implications for vaccination in early life, are aspects that are discussed in this review

The dog that did not bark: malaria vaccines without antibodies.

Item does not contain fulltextTo date, the only pre-blood stage vaccine to confer protection against malaria in field trials elicits both antigen-specific antibody and T-cell responses. Recent clinical trials of new heterologous prime-boost malaria vaccine regimens using DNA, fowlpox or MVA, have chiefly elicited T-cell responses that have promisingly reduced hepatic merozoites in challenge trials, but failed to protect in field trials. These encouraging results suggest further augmentation of T-cell responses to pre-blood stage antigens might one day contribute to a highly protective vaccine. We envision that a highly protective pre-erythrocytic vaccine will likely be based upon a heterologous prime-boost regimen that induces both appropriate T-cell responses as well as robust and protracted antibody production

Influenza virosomes: a flu jab for malaria?

Item does not contain fulltextThe major attractions of vaccines based on viral carriers (vectors) include their immunogenicity without adjuvant and the relative simplicity of their associated production processes in comparison with recombinant protein-based approaches. Two influenza virosomal vaccines - for influenza and hepatitis A - are registered for human use, and the virosome platform is being evaluated as the carrier for a Plasmodium falciparum vaccine that targets both the exo-erythrocytic and erythrocytic stages. Although safe and immunogenic, the first such virosome-based malaria vaccine showed no protection in a Phase IIa clinical trial. Nevertheless, the established safety profile of virosomes and their flexibility with regard to antigen delivery - allowing for antibody induction via the conjugation of peptides and T-cell induction via encapsulation - indicate that they warrant further exploration

The multiplicity of Plasmodium falciparum infections is associated with acquired immunity to asexual blood stage antigens.

Item does not contain fulltextWe evaluated the relationship between immune response markers and the multiplicity of Plasmodium falciparum infections in order to assess the validity of the latter as an indicator of the acquisition of anti-malarial immunity. Parasite populations present during malaria episodes of 64 Gabonese children who presented with at least 4 such attacks during active follow-up over a 7-year period were characterized using MSP-1 and MSP-2 PCR-based methods. Plasma samples taken at healthy and parasite-free phase were used to measure P. falciparum antigen-specific antibody and cytokine activity. We found evidence of intra- and inter-individual variation in the number of parasite genotypes present in different malaria episodes, although in 72% of isolates no more than 2 parasite genotypes were detectable. Samples with the highest multiplicity were from children with significantly lower (p < 0.03) antibody responses to specific asexual stage antigens. Additionally, the whole blood interferon-gamma production capacity was significantly higher (p < 0.02) in those with lower infection multiplicity. Malaria episodes with multiple clones indeed reflect a low level of acquired immunity and a consequently poor capacity to control the infection. These findings suggest that the multiplicity of falciparum infection may be a potentially useful parameter in the evaluation of malaria control interventions

Reduced cord blood immune effector-cell responsiveness mediated by CD4+ cells induced in utero as a consequence of placental Plasmodium falciparum infection.

Contains fulltext : 50468.pdf (publisher's version ) (Closed access)To determine mechanisms of neonatal parasite antigen (Ag)-specific immune suppression associated with placental Plasmodium falciparum infection, we isolated cord blood mononuclear cells (CBMCs) from Gabonese neonates born to mothers with differing histories of P. falciparum infection and performed ex vivo and in vitro studies to evaluate immune regulatory activity. We found increased ex vivo percentages of CD4(+)CD25(hi) and CD4(+)CD25(+)CTLA-4(+) cells and increased interleukin (IL)-10 responses to parasite Ag in vitro in CBMCs from neonates born to mothers with placental P. falciparum infection at delivery. Depleting CBMCs of CD4(+)CD25(+) cells before cell culture led to the abrogation of parasite Ag-specific IL-10 responses, to enhanced interferon- gamma responses, and to enhanced expression of CD25 on CD8(+) T cells and of major histocompatibility complex class I and II on monocytes. These data demonstrate that parasite Ag-specific CD4(+) regulatory cells are generated in utero as a consequence of placental P. falciparum infection

ABO blood group and the risk of placental malaria in sub-Saharan Africa

Background: In malarious areas of the world, a higher proportion of the population has blood group O than in non-malarious areas. This is probably due to a survival advantage conferred either by an attenuating effect on the course of or reduction in the risk of infection by plasmodial parasites. Here, the association between ABO blood group and incidence of placental malaria was assessed in order to determine the possible influence of the former on the latter. Methods: Data from a study in Lambarene, Gabon, and data from three previously published reports of studies in The Gambia, Malawi and Sudan, were compiled and compared. ABO blood groups were cross-tabulated with placental malaria stratified by parity. Odds ratios (OR), stratified by parity, were calculated for the outcome, placental parasitaemia, and compared between blood group O vs. non-O mothers in all four studies. Random effects meta-analysis of data from individual studies from areas with perennial hyper/holoendemic transmission was performed. Results: In Gabon, the odds ratio (OR) for active placental parasitaemia in mothers with group O was 0.3 (95% CI 0.05-1.8) for primiparae and 0.7 (95% CI 0.3-1.8) for multiparae. The OR for primiparae in the published study from The Gambia was 3.0 (95% CI 1.2-7.3) and, in Malawi, 2.2 (95% CI 1.1-4.3). In the Sudanese study, no OR for primiparae could be calculated. The OR for placental parasitaemia in group O multiparae was 0.8 (95% CI 0.3-1.7) in the Gambia, 0.6 (95% CI 0.4-1.0) in Malawi and 0.4 (95% CI 0.1-1.8) in Sudan. Combining data from the three studies conducted in hyper-/holo-endemic settings (Gambia, Malawi, Gabon) the OR for placental malaria in blood group O multiparae was 0.65 (95% CI 0.44-0.96) and for primiparae 1.70 (95% CI 0.67-4.33). Conclusion: Studies conducted in The Gambia and Malawi suggest that blood group O confers a higher risk of active placental infection in primiparae, but a significantly lower risk in multiparae. These findings were not confirmed by the study from Gabon, in which statistically non-significant trends for reduced risk of placental parasitaemia in those with blood group O, regardless of parity, were observed.Host-parasite interactio