In a PD-1 defective animal model, researchers observed delayed-onset, organ-specific autoimmune diseases, including lupus-like syndrome and autoimmune-dilated cardiomyopathy, indicating the lymphocytes inhibit the functions of PD-1 (Nishimura et al., 1999; Okazaki et al., 2003). Here, PDCD1 is linked to autoimmune disease.