CD4 and colitis: While the transfer of Ihh HET CD4+ T cells potently induced colitis, transfer of Ihh KO CD4+ T cells showed strongly diminished colitis indicated by reduced weight loss (Fig. 6g), reduced colon thickening/shortening (Fig. 6h) and reduced mucosal infiltration of T cells expressing IL-17a, IL-22 and IFNγ in the colon (Fig. 6i and Supplementary Fig. 9).