IL-21 is over-produced in the intestine of IBD patients, but the vast majority of IL-21-producing CD4+ T cells co-express IFN-γ and not IL-17A, thus suggesting that Th1 and not Th17 cells are major sources of IL-21 in the human gut [32,33] (Figure 1). The gene discussed is IL17A; the disease is inflammatory bowel disease.