In addition to promoting B cell responses, IL-21 has also been shown to be an important factor for the differentiation of the Th17 lineage [6, 26, 27]; therefore, the increase in IL-17-producing cells in type 1 diabetes patients as compared with healthy controls observed in the current study, as well as in previous studies [4–6], could be a consequence of increased IL-21 production. This evidence concerns the gene IL21 and type 1 diabetes mellitus.