Fig. 1　Roles of Sox5 and c-Maf in the production of IL-17A and IL-21. Under Th17-differentiating conditions, IL-6 induces Sox5 expression in CD4＋ T cells in a Stat3-dependent manner. Additionally, IL-6 induces c-Maf expression especially in the presence of TGF-β. Sox5 and c-Maf co-induce IL-17A production via induction of RORγt. c-Maf induces IL-21 by binding to the IL-21 promoter and CNS-2 enhancer. On the other hand, TGF-β inhibits c-Maf-induced IL-21 production in CD4＋ T cells. TGF-β-induced Foxp3 binds to IL-21 promoter and CNS-2 enhancer and inhibits c-Maf-induced IL-21 production in CD4＋ T cells.