PD-1 deficiency in mice leads to the development of various autoimmune disorders, such as dilated cardiomyopathy associated with autoantibody production in BALB/c mice, systemic lupus erythematosus-like glomerular nephritis and arthritis in C57BL/6 mice, myocarditis associated with generation of autoantibody in MRL mice, and accelerated type 1 diabetes in non-obese diabetic mice, suggesting that PD-1 is involved in the suppression of autoimmune reactions [7, 8]. Here, PDCD1 is linked to myocarditis.