The key physiological function of PD-1 had become clear when knockout mice obtained: PD-1 deficient mice develop different autoimmune diseases depending on their genetic background: C57BL/6-Pdcd1−/− mice develop lupus-like arthritis and glomerulonephritis with predominant IgG3 deposition [20]. The gene discussed is PDCD1; the disease is arthritic joint disease.