T-helper 17 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, T-helper 17 (Th17) cells have been linked to tissue injuries, while regulatory T cells (Tregs) are thought to downmodulate inflammatory reactions. We assessed whether bladder pathology in human Schistosoma haematobium infection is related to the balance of Th17 cells and Tregs. We used a murine model of Schistosoma mansoni infection to further investigate whether the peripheral profiles reflected ongoing events in tissues. Methods. We characterized T-helper cell subsets in the peripheral blood of children residing in a S. haematobium- endemic area and in the peripheral blood, spleen, and hepatic granulomas of S. mansoni-infected highpathology CBA mice and low-pathology C57BL/6 mice. Results. 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 infected children with pathology, compared with infected children without pathology. Percentages of interleukin 17-producing cells were significantly higher in spleen and granulomas of CBA mice, compared with C57BL/6 mice. This difference was also reflected in the peripheral blood. Conclusions. This is the first study to indicate that Th17 cells may be involved in the pathogenesis of human schistosomiasis.