MFIs of PD-1 on the surface of CD4+ lymphocytes obtained from PBMCs and LNCs were significantly higher in the lymphoma group (PBMCs, 1169 ± 573, P = 0.004; LNCs, 2655 ± 1116, P < 0.001) than in the control group (PBMCs, 617 ± 262; LNCs, 933 ± 375; S2 Fig). Here, CD4 is linked to lymphoma.