IL17A and Crohn ileitis: Consistent with the development of ileitis, elevated numbers of effector CD4+ T cells including IFN-γ+, IL-17+ and IFN-γ+ IL-17+ CD4+ T cells were present in the lamina propria of the small intestines of Batf2−/− mice compared with wild-type mice, but no changes in the number of IL-10+ CD4+ T cells were observed (Supplementary Figure 1B).