Similar to IL-10, PD-1 plays a prominent role in maintaining peripheral tolerance, and several studies note that elimination of this pathway leads to the development of autoimmune disorders in animal models, with PD-1 signaling-deficient mice developing conditions including Lupus-like proliferative arthritis and autoimmune dilated cardiomyopathy [95,96]. Here, PDCD1 is linked to systemic lupus erythematosus.