CD4 and colitis: Although genetic deletion of IL-15 (i.e. using IL-15 whole-body KO mice) is not successful in treating DSS-induced colitis model in mice (144) (Table 3), adoptive transfer of B6 CD4+ T cells to IL-15-deficient Rag KO mice induces colonic inflammation compared to the control, and adoptive transfer of IL-15 receptor-deficient Treg fails to suppress severe colonic inflammations with extensive mucosa damage in CD4+ T cell transfer colitis model (55) (Table 3), suggesting a direct role of IL-15 in colitogenic CD4+ T cells.