CD8A and autoimmune disease: The co-inhibitory receptor T cell immunoglobulin and mucin-domain containing protein-3 (TIM-3) was originally discovered in our laboratory as a surface protein specifically expressed on Th1 cells and IFNγ-producing CD8+ T cells.89 As Th1 cells are established drivers of autoimmune disease, the function of TIM-3 was first studied in models of autoimmunity and it became apparent that TIM-3 mediates a potent inhibitory function.