In mice, IL-21 is overproduced in models of autoimmune diabetes (94, 95), and deficiency in IL-21R was found to prevent the development of diabetes in non-obese diabetic (NOD) mice, while transgenic expression of IL-21 in pancreatic islets was sufficient to trigger diabetes in non-autoimmune C57BL/6 mice (95, 96). This evidence concerns the gene IL21R and diabetes mellitus.