Insulin as a T cell antigen in type 1 diabetes supported by the evidence from the insulin knockout NOD mice

Rodents have two functional preproinsulin genes named insulin 1 and insulin 2 on different chromosome and have two amino acid differences in insulin B chain. We have established insulin 1 or insulin 2 knockout (KO) non-obese diabetic (NOD) colonies in the animal institute of Kobe University and evaluated anti-insulin autoimmunity. Similar to the previous report, insulin 1-KO provides strong protection from insulitis (islet-infiltration of mononuclear cells) and diabetes, whereas the insulin 2-KO markedly accelerated insulitis and development of diabetes even at further backcross breeding with NOD/Shi/Kbe mice (P<0.0001). Expression of serum anti-insulin autoantibodies (IAA) was enhanced in insulin 2-KO mice at a time between 10 and 15 weeks of age (P<0.005) while the expression of insulin 1-KO NOD mice was rather reduced. Furthermore, T cell reactivity in splenocytes of insulin 2-KO NOD mice to insulin 1 B:9-23 peptide was increased (P<0.05), suggesting that expanding insulin-reactive T cells may contribute to the acceleration of diabetes in insulin 2-KO mice. Based on those observations, we hypothesize that insulin 1 is a crucial T cell antigen in murine autoimmune diabetes and modification of anti-insulin autoimmunity can be applicable to antigen-based therapy for human type 1 diabetic patients.