PD-1 blockade enhances white and red pulp T cell motility at a later stage of exhaustion. (A and B) Mean track velocities (µm/min) of CD8⁺ P14 and CD4⁺ SMARTA cells were quantified in the splenic white (A) and red (B) pulp at day 14 after infection (n = 4 mice). 4 h before imaging, anti–PD-1 or isotype control antibodies (500 µg) were injected intravenously. Asterisks denote statistically significant differences (P < 0.05). Each dot represents the track of an individual T cell. Horizontal black bars denote the mean of each group.