IDO1 and Cowden disease: [5] Among these include exertion of antimicrobial activity, suppression of activated T-cell responses and induction of regulatory T-cells. Thus, acting as a natural break to ongoing inflammation, it is not surprising that increased IDO1 expression has been identified in active IBD and CD. [6], [7] Mechanistic studies using experimental models have advanced our knowledge by revealing that inhibition of IDO1 leads to worsened colitis severity [8], while pharmacologic induction of IDO1 can limit colitis severity and promote epithelial restitution [9], [10].