Enhancement of cytokine production by anti-PD-1 mAb in bovine lymphocytes. PBMC were cultivated with rat IgG control or four types of anti-PD-1 mAb (20 μg/mL) in the absence (a; n = 8 or 14) or presence (b; n = 16) of PMA/ionomycin. IFN-γ production was measured by ELISA. Statistical comparisons between rat IgG control and anti-PD-1 mAb were made using the Wilcoxon matched-pairs test. Differences were considered statistically significant at P < 0.05 (*P < 0.05; ** P < 0.01).