Our study clearly showed that during the course of S. japonicum infection, in parallel with the increase of the proportion of Th17 cells, both the inducing (TGF-β, IL-6, IL-21 and IL-23) and inhibitory (IFN-γ, IL-4, Th1, Th2 and Treg cells) factors of Th17 cell generation increased as the infection progressed. The gene discussed is IL21; the disease is infection.