| Type 1 Diabetes (T1D) is a polygenic autoimmune disease characterized by immune cell infiltration into the islets of Langerhans, destruction of insulin-producing beta cells, and uncontrolled hyperglycemia. Islet-antigen reactive CD4+ and CD8+ T cells, and regulatory T cells (Tregs) are the major players in T1D pathogenesis. Both cell-intrinsic and cellextrinsic inhibitory mechanisms are required to maintain self-tolerance to islet-antigens.;Lymphocyte Activation Gene 3 (LAG3, CD223), a co-inhibitory receptor highly expressed on T cells, is one of these essential mechanisms that intrinsically regulate T cell tolerance in autoimmune diabetes. I evaluate the role of LAG3 on T cells versus non- T cells, CD8+ T cells, and Tregs by generating mice in which LAG3 is specifically absent on these subsets in a murine model of T1D. In Chapter 3, I show that the predominant expression of LAG3 on insulitic CD4+ and CD8+ T cells is required to limit the pathogenesis of autoimmune diabetes in non-obese diabetic (NOD) mice. The loss of LAG3 on CD8+ T cells alone is sufficient to promote early onset of autoimmune diabetes by promoting islet-specific glucose-6-phophatase catalytic subunit-related protein (IGRP)-reactive CD8 + T cells to differentiate into effector T cells. In Chapter 4, I show that LAG3 is preferentially and constitutively expressed on a subset of insulitic Tregs, and loss of LAG3 on Tregs leads to delayed onset and reduced incidence of autoimmune diabetes. LAG3 may intrinsically limit Treg proliferation and functionality by repressing pathways that promote the maintenance of Tregs in the pancreas of NOD mice.;In addition to dissecting the role of LAG3 in regulating T cell tolerance, I also show that removal of programmed death protein 1 (PD1) or overexpression of Neuropilin 1 (Nrp1) on Tregs protect NOD mice from autoimmune diabetes in Appendix A and Appendix B, respectively. In summary, my findings have advanced our understanding of cell-intrinsic mechanisms that regulate T cell tolerance in autoimmune diabetes. |
