We found that while wt Treg cells prevent the colitis, as evidenced by a normal colon morphology, the Rbx1-deficient Treg cells failed to do so, and the mice developed very severe colitis, similar to the control mice without receiving Treg cell injection (Fig. 2a), demonstrating that the immune suppressive function of Treg cells was indeed impaired upon Rbx1-deletion. This evidence concerns the gene RBX1 and colitis.