IL17A and colitis: Moreover, in line with reports indicating that IFN-γ and IL-17 are the main immune mediators in Th1/Th17-type IBD12 and that Th17 cells are plastic and can secrete not only IL-17-type cytokines but also IFN-γ (ref. 27), we found significantly higher mean fluorescence intensity values for IFN-γ and IL-17 production in the colon and ILN of IL-15-deficient mice with colitis (Fig. 6b–d).