ICOS enhances follicular T helper responses and deteriorates the pathogenic process of liver in mice infected with Schistosoma japonicum

BackgroundHumoral immune responses play an important role in mediating liver granulomatous inflammation and fibrosis in schistosomiasis. Follicular helper T (Tfh) cells have a central role in mediating humoral immune responses. Generation of Tfh cells depends on inducible T cell costimulator (ICOS) signaling, but the underlying molecular mechanisms are incompletely understood in pathogenesis of schistosomiasis. Methodology/Principal FindingsWe used a strain of ICOS-transgenic (Tg) mice to test the degrees of liver granulomatous inflammation and fibrosis, the frequency of splenic Tfh cells and soluble egg antigen-specific cytokine responses longitudinally in mice following Schistosoma japonicum (S. japonicum) infection. In comparison with that in wide-type (WT) mice, significantly severer liver granulomatous inflammation and fibrosis and higher mortality were observed in ICOS-Tg mice. Significantly higher frequency of splenic Tfh cells was accompanied by significantly higher levels of Bcl-6 and CXCR5 expression in the livers of ICOS-Tg mice. Furthermore, significantly higher levels of SEA-specific IL-4, IL-6, IL-10, IL-13, IL-17A, IL-21 and TGF-{beta}1 responses, but lower levels of IFN-{gamma} responses were detected in ICOS-Tg mice, which were abrogated by treatment with ICOS blockers in vitro. In addition, significantly higher levels of serum anti-SEA IgG were detected in ICOS-Tg mice. Conclusions/SignificanceThe ICOS-related signaling may promote the pathogenesis of murine schistosomiasis by polarizing Tfh cells, which may be immune check points for the prevention and intervention of schistosomiasis. Author summaryGranulomatous inflammation and fibrosis in the liver are the major pathogenic characteristics of schistosomiasis. ICOS is crucial for the development of Tfh cells, which are the key modulators of B cell activation and humoral immunity. However, the underlying molecular mechanisms are incompletely understood in pathogenesis of schistosomiasis. Here, our results showed that the ICOS over-expression would significantly induce severer liver inflammation and fibrosis, higher frequency of splenic Tfh, higher levels of anti-SEA IgG as well as imbalanced SEA-specific cytokine responses in ICOS-Tg mice. The findings suggested that ICOS signaling may promote the pathogenesis of murine schistosoma-related liver inflammation and fibrosis by polarizing Tfh cells. Potentially, ICOS signaling and Tfh cells may be immune check points for the prevention and intervention of schistosomiasis.