Chromogranin A Deficiency Confers Protection from Autoimmune Diabetes Via Multiple Mechanisms

Recognition of beta-cell antigens by autoreactive T cells is a critical step in the initiation of autoimmune Type1 diabetes (T1D). A complete protection from diabetes development in non-obese diabetic (NOD) mice harboring a point mutation in the insulin B-chain 9-23 epitope points to a dominant role of insulin in diabetogenesis. Generation of NOD mice lacking the Chromogranin A protein (NOD.ChgA^-/-) completely nullified the autoreactivity of the BDC2.5 T cell and conferred protection from diabetes onset. These results raised the issue concerning the dominant antigen that drives the autoimmune process. Here we revisited the NOD.ChgA^-/- mice and found that their lack of diabetes development may not be solely explained by the absence of Chromogranin A reactivity. NOD.ChgA^-/- mice displayed reduced presentation of insulin peptides in the islets and periphery, which corresponded to impaired T cell priming. Diabetes development in these mice was restored by antibody treatment targeting regulatory T cells or inhibiting TGFb and PD-1 pathways. Therefore, the global deficiency of chromogranin A impairs recognition of the major diabetogenic antigen insulin, leading to broadly impaired autoimmune responses controlled by multiple regulatory mechanisms.