Differential immune response to B:9-23 insulin 1 and insulin 2 peptides in animal models of type 1 diabetes

Abstract

Mice have two insulin genes that differ in the insulin sequence by two amino acids, including the B9 position. Given prior studies of the B:9-23 insulin peptide in NOD mice, a fundamental question is whether the immune response to the B:9-23 peptide of the two insulins is identical. We investigate responses to the immunization with B:9-23 insulin 1 and 2 peptides in NOD and RIP-B7.1 Balb/c mice. NOD and F1 (Balb/c × C57/Bl6) B7.1 transgenic mice were given either B:9-23 insulin 1, B:9-23 insulin 2 or tetanus toxoid (TT) control peptide. Insulin autoantibodies (IAA), and anti-B:9-23 antibodies (IgG 1 and IgG 2c) were measured. Subcutaneous injection of the insulin 2 but not the insulin 1 peptide significantly protected NOD mice from diabetes. Conceptually similar, insulin 1 peptide immunization accelerated diabetes in the B7.1 mice compared with insulin 2 peptide. Insulin 1 and 2 peptides induced similar levels of IAA in the NOD mice except at week 26, where insulin 2 induced higher levels of IAA. Anti-IgG 1 B:9-23 peptide antibodies were higher in the insulin 2 immunized group of NOD mice, while IgG 2c anti-B:9-23 peptide antibodies were higher in the insulin 1 group. Adoptive transfer of splenocytes from insulin 1 immunized mice to NOD. scid mice demonstrated accelerated diabetogenicity. The protection afforded by insulin 2 peptide but not insulin 1 peptide in the NOD mouse is reflected by its predominant Th2 humoral response. This may relate to the protection conferred by the insulin 1 knockout when bred onto NOD mice in contrast to acceleration of disease with an insulin 2 knockout.