(a) CD4+ T cells isolated from wild-type (WT) and Cd4-cre;Smad4fl/fl (SMAD4 KO) mice were cultured with IL-21 and TGF-β receptor I inhibitor. After 1, 2, 3, and 4 days, IL-17A+ cells were analyzed by flow cytometry. Representative results and statistical analysis are shown. (b) The relative mRNA amounts of Th17-related genes on day 4 were analyzed by qRT-PCR. (c) CD4+ T cells isolated from wild-type (WT) and CD4-cre;Smad4fl/fl;Tgfbr2fl/fl (SMAD4-TGFβRII DKO) mice were cultured with IL-21. After 1, 2, 3, and 4 days, IL-17A+ cells were analyzed by flow cytometry. Representative results and statistical analysis are shown.