For instance, the injection of anti-CTLA-4 mAb was shown to ameliorate trinitrobenzene sulfonic acid (TNBS)-induced colitis by increasing indoleamine 2,3 dioxygenase (IDO) expression and inducing IL-10-producing ICOS+ Treg expansion in the mesenteric lymph nodes and inflamed colon (112). Here, ICOS is linked to colitis.