CD4 and type 1 diabetes mellitus: There is evidence from mouse models for a role of the IL-21 pathway in type 1 diabetes [9], but aside from the established IL2-IL21 region association with type 1 diabetes risk [10], we have only identified one published, recent study that reported increased frequencies of circulating CD4+ T follicular helper (Tfh) cells together with enhanced expression of IL-21 in type 1 diabetes patients [8].