Recognition of PD-1-expressing cells by anti-PD-1 mAb. (a) Flow cytometric analysis of surface expression of bovine PD-1. Cos-7 expressing PD-1 (black line) and Cos-7 transfected with the control vector (dashed line) were stained with four types of anti-PD-1 mAb (2C12, 2H7, 3G2, and 5D2) and isotype control (Rat IgG). (b) Western blotting analysis of bovine PD-1 expression in CHO-DG44 cells stably expressing bovine PD-1. Three types of anti-PD-1 mAb recognized PD-1 (triangle) at about 68 kDa. Anti-actin antibody and anti-myc antibody was used as a loading control and a positive control.