CD4 and colitis: Strikingly, following T-cell transfer, Rag1−/−Cre+ recipient mice showed marked growth retardation compared with Rag1−/−Cre− control mice (Fig. 2b), together with severe colitis associated with accumulation of CD4+ T cells and expression of mRNA for tumour necrosis factor-α, inducible nitric oxide synthase, interferon (IFN)-γ and interleukin (IL)-17A (Figs. 2b–f).