Decreased atopy in children infected with Schistosoma haematobium: a role for parasite-induced interleukin-10

Background Most of the effort directed at understanding the role infections have in preventing allergy has focused on bacteria and viruses and their a bility to divert the immune system towards T-helper-1 responses and away fr om proallergic T-helper-2 responses. However, helminth infections, highly p revalent in large parts of the developing world, where allergy is uncommon, stimulate strong T-helper-2 responses. We investigated the influence of ch ronic helminth infections on the prevalence of atopy and aimed to understan d the relation at a detailed immunological level. Methods 520 Gabonese schoolchildren were tested for shin reaction to house- dust mite and other allergens, for Schistosoma haematobium eggs In urine, a nd for microfilariae in blood samples. Total and mite-specific IgE antibodi es were measured. A subsample selected on the basis of their skin test to h ouse-dust mite received detailed immunological investigations. Findings Children with urinary schistosomiasis had a lower prevalence of a positive skin reaction to house-dust mite than those free of this infection (odds ratio 0.32 [95% CI 0.16-0.63]). The degree of sensitisation to house -dust mite could not explain this difference in skin-prick positivity. Schi stosome-antigen-specific concentrations of interleukin-10 were significantl y higher in infected children, and higher specific concentrations of this a nti-inflammatory cytokine were negatively associated with the outcome of sk in-test reactivity to mite (0.53 [0.30-0.96]). No association between polyc lonal IgE antibodies and skin-test results was found. Interpretation The anti-inflammatory cytokine, interleukin-10, induced in c hronic schistosomiasis, appears central to suppressing atopy in African chi ldren.