Th17 cells are associated with pathology in human schistosomiasis

Background. Schistosome infections are often clinically silent, but some individuals develop severe pathological reactions. In several disease processes Th17 cells have been linked to tissue injuries, while regulatory T (Treg) cells are thought to down-modulate inflammatory reactions. We assessed whether bladder pathology in human Schistosoma haematobium infection is related to the balance of Th17 and Treg cells. Using a murine model of Schistosoma mansoni infection we further investigated whether the peripheral profiles reflected ongoing events in tissues. Methods. We characterized T helper subsets in the peripheral blood of children residing in a S. haematobium-endemic area and in peripheral blood as well as in spleen and hepatic granulomas of S. mansoni-infected high-pathology CBA and low-pathology C57BL/6 mice. S. haematobium-infected children with bladder pathology had a significantly higher percentage of Th17 cells than those without pathology. Moreover, the Th17/Treg ratios were significantly higher in children with pathology compared to infected children without pathology. Results. Percentages of IL-17-producing cells were significantly more abundant in the spleen and granulomas of CBA compared to C57BL/6 mice. This difference was also reflected in the peripheral blood. Conclusions. Our results indicate for the first time that Th17 cells may be involved in the pathogenesis of human schistosomiasis.