Recent data have also shown that IL-17A, by directly binding to its receptor (IL-17R) expressed on Th1 cells, inhibits Th1 cell-mediated colonic inflammation [18].Together, these data suggest that IL-17A plays both a pro-inflammatory and an anti-inflammatory role in IBD, which might explain the failure of the clinical trial targeting IL-17A. Here, IL17RA is linked to colitis.