IFNG and colitis: Overall, IDO-1 induced by IFN-γ and KYNA catalyzes tryptophan metabolism to produce KYN or KYNA in hADSCs, promotes hADSCs homing and the polarization of intestinal macrophages to the anti-inflammatory M2 and increases the expression of IL-10 to inhibit inflammation, and consequently alleviates colitis and colon fibrosis (Fig. 7).