IL17A and colitis: In particular, studies examining mouse and human colonic tissue have reported on IL-17A+ CD4+ T cell or IFNγ+IL-17A+ CD4+ T cell populations that has been shown to exacerbate colitis severity (Cosmi et al., 2008; Ahern et al., 2010; Chudnovskiy et al., 2016; Britton et al., 2019; Schirmer et al., 2019).