IL4 and graft versus host disease: Furthermore, that helminth infection did not promote T cell IL-4 production or, after TBI, T lymphocyte survival in a mouse model with T cell–specific deficiency of IL-4Rα (CKO mice) indicates that the Th2 cytokine IL-4 acts directly on T cells, attesting to the autocrine IL-4 and Th2 regulatory loop in alleviating GVHD.