Pathogenesis of NOD Diabetes is Initiated by Reactivity to the Insulin B Chain 9–23 Epitope and Involves Functional Epitope Spreading1

Type 1 diabetes (T1D) is mediated by destruction of pancreatic β-cells by CD4 and CD8 T cells specific for epitopes on numerous diabetogenic autoantigens resulting in loss of glucose homeostasis. Employing antigen-specific tolerance induced by i.v. administration of syngeneic splenocytes ECDI cross-linked to various diabetogenic antigens/epitopes (Ag-SP), we show that epitope spreading plays a functional role in the pathogenesis of T1D in NOD mice. Specifically, Ag-SP coupled with intact insulin, Ins B(9-23) or Ins B(15-23), but not GAD65(509-528), GAD65(524-543) or IGRP(206-214), protected 4-6 week old NOD mice from the eventual development of clinical disease; infiltration of immune cells to the pancreatic islets; and blocked the induction of DTH responses in a Treg-dependent, antigen-specific manner. However, tolerance induction in 19-21 week old NOD mice was effectively accomplished only by Ins-SP, suggesting Ins B(9-23) is a dominant initiating epitope, but autoimmune responses to insulin epitope(s) distinct from Ins B(9-23) emerge during disease progression.