Antibody responses to helminth parasite antigens in malaria endemic populations.

Introduction Co-infection with P. falciparum and helminths in Sub-Saharan Africa could modulate the immune response towards the parasites as well as susceptibility to disease (Salgame et al. Nat Rev Immunol 2013). Our aim is to investigate the impact of helminth infections on the different immunity to malaria shown by ethnic groups from Burkina Faso (Modiano et al. PNAS 1996). Specific objectives are: i) to measure immunoglobulins against helminth parasite antigens in plasma samples collected among Mossi, Fulani and Rimaibe populations; ii) to assess differences in prevalences and levels of specific IgG in relation to age, sex, village, ethnic group, and infection with P. falciparum. Material and methods Plasma samples were collected during a cross-sectional survey conducted in August 2007 in rural villages of Burkina Faso. A subset of samples (N=288) was assayed by ELISA to measure IgG against: i) Strongyloides stercoralis antigens (Bordier Affinity); ii) filarial nematodes antigens (Bordier Affinity) iii) Schistosoma haematobium Soluble Egg Antigen (SEA, Mutapi et al. Paras Immunol 1997). Results The prevalence of IgG against antigens of Strongyloides stercoralis, filarial nematodes and Schistosoma hematobium is 5%, 16%, 63% respectevely. These measures lye within the infection prevalence ranges as obtained by direct diagnosis, suggesting ELISA may be suitable for population screening and evaluation of control programmes. The prevalence of anti-SEA IgG is zero in infants, increases during childhood to reach its peak in teens, and decreases from 20 years onwards. Females show a lower prevalence than males (P=0.003). Differences in prevalence are not observed among villages or ethnic groups, but the Fulani show lower levels of anti-SEA IgG (P=0.0001) indicating that lighter S. haematobium infections may occur in the ethnic group known for a marked lower susceptibility to P. falciparum. Individuals infected with P. falciparum show higher levels of anti-SEA IgG (P=0.0002) suggesting that common host factors may affect susceptibility to P. falciparum and S. haematobium (e.g. age, ethnicity). Conclusions Experimental models indicate that helminths Excretory/Secretory molecules induce Dendritic Cells to produce immunoregulatory cytokines (TGFβ, IL10) promoting the expansion of Tregulatory cells (Tregs) and the suppression of effector responses against intracellular pathogens such as malaria (Salgame et al. Nat Rev Immunol 2013). The malaria resistant Fulani population have been previously described to show lower levels of TGFβ and lower number of Tregs (Torcia et al. PNAS 2008). The observation of lower anti-SEA IgG levels in the Fulani warrants further investigation into the immunological cross-talk between S. haematobium and P. falciparum in this population.