Identification of a New Pathogenic Hybrid Insulin Peptide-Specific CD4 T cell Capable of Inducing Autoimmune Diabetes
Type 1 diabetes (T1D) is an autoimmune disease in which autoreactive T cells target and destroy insulin-producing β cells in the pancreas, leaving patients reliant on insulin-based therapies. T cells specific for hybrid insulin peptides (HIPs) have previously been isolated from individuals with T1D and are one component considered to trigger an autoimmune response. In the non-obese diabetic (NOD) mouse, HIPs are loaded onto MHCII and recognized by I-Ag7-restricted 4.1-T cell receptors. The activated CD4 T cell becomes autoreactive and activates B cells and CD8 T cells to attack the β cells. T cells with specificity for HIPs can be detected through tetramer staining. This study aims to validate a novel tetramer containing an epitope derived from the C chain of insulin (HIP39) and to determine HIP39-specific T cells' role in diabetes pathogenesis. To determine if HIP39-specific T cells are present in the pancreas of non-obese diabetic mice, tetramer staining was performed. The tetramer was validated by comparing naive mice to immunized mice, and it was hypothesized that HIP39-specific T cells would expand in the lymph nodes and spleen in response to immunization with HIP39 peptide in Complete Freund’s adjuvant. A significant expansion of HIP39-specific CD4 T cells was observed in the spleen and lymph nodes of immunized NOD mice compared to naïve mice. Following tetramer validation, HIP39-specific T cells from immunized NOD mice were transferred to an immunocompromised mouse to determine if those T cells were sufficient to cause diabetes in a mouse lacking other immune cells, including CD4 and CD8 T cells. It was found that the recipient mouse developed diabetes 20 days after injection with HIP39-specific CD4 T cells. These data suggest that HIP39 elicits an immune response and HIP39-specific T cells are a causative agent of diabetes.