PDCD1 and Autoimmunity: To prevent autoimmunity against self-antigens, T-cells have inhibitory ligands such as cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) or programmed-cell-death-protein-1 (PD-1) that compete for binding to APC ligand CD80 which result in T-cell anergy by inhibiting intracellular signaling.