PDCD1 and autoimmune disease: The co-inhibitory molecules cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), programmed cell death 1 (PD-1), and programmed cell death-ligand 1 (PD-L1), also known as immune checkpoints (IC), act on peripheral immune tolerance regulating the response to self-proteins, inhibiting the destruction of healthy tissues, and preventing autoimmune diseases (Nirschl and Drake, 2013).