CD4 and inflammatory bowel disease: Regulatory [Treg] and effector [Teff] CD4+ T cells are important mediators of the immune response in the gut of IBD patients, with defects in Treg number and suppressive function noted in the lamina propria and peripheral blood of patients with active IBD.4,5 Additionally, many identified IBD genetic risk loci map to immune cell enhancer regions, with particular enrichment in CD4+ T cell enhancers.6 Treg are characterised by high constitutive expression of the IL-2 receptor alpha chain [IL2RA, CD25], a component of the high-affinity IL-2 receptor heterotrimer [IL2Rα/β/γ].