RBX1 and colitis: We then performed the in vivo suppression assay in Rag1−/− immunodeficient mice to confirm the role of Rbx1&Sag deficiency in the suppressive function of Treg cells and found that the Rbx1&Sag-deficient Treg cells failed to prevent the colitis induced by Tnai cells (Fig. 5A), indicating impaired suppressive function.