CD4 and type 1 diabetes mellitus: In type 1 diabetes (T1D), insulin-producing β cells are attacked by autoreactive CD4+ and CD8+ T cells that infiltrate the pancreatic islets in a process called insulitis.38 Several self-antigens such as glutamic acid decarboxylase (GAD), insulinoma antigen-2 (IA-2), insulin, and zinc transporter 8 (ZNT8) stimulate autoreactive T cells in T1D.