PD-1 deficiency (PD-1-/-) causes lupus-like glomerulonephritis and arthritis in C57BL/6 mice [2,3], autoimmune dilated cardiomyopathy (DCM) and gastritis in BALB/c mice [4,5], acute type 1 diabetes mellitus (T1DM) in nonobese diabetic (NOD) mice [6], and lethal myocarditis in MRL mice [7]. Here, PDCD1 is linked to arthritic joint disease.