Role of TCR downmodulation and of the PD-1 axis on T cell stop. (A and B) GFP⁺ OT-I CD8⁺ T cells were adoptively transferred, and recipients were stimulated by an i.v. injection of OVAp or left untreated as a control. (A) Kinetics of CD3ε (left) or PD-1 (right) surface expression on OT-I CD8⁺ T cells as determined by flow cytometry. Data are shown as mean ± SEM. (B) The surface expression of the indicated markers was assessed on GFP⁺ OT-I CD8⁺ T cells at 48 h in peptide-injected or untreated recipients. Data are representative of three independent experiments. (C) Anti­–PD-1 treatment does not restore the ability of activated T cells to arrest upon antigenic peptide injection. GFP⁺ OT-I CD8⁺ T cells were adoptively transferred, and recipients were stimulated by an i.v. injection of OVAp. Mice were treated with anti–PD-1 or isotype control on day 1. Intravital imaging of the popliteal lymph node was performed on day 2. OVAp was reinjected during the imaging experiment. Velocity and arrest coefficient of individual T cells are shown in mice treated with anti–PD-1 or an isotype control before and after OVAp reinjection. Results are representative of two independent experiments. Each dot represents an individual track. Significance testing were performed with the nonparametric Mann-Whitney test. ***, P < 0.001. Also see Fig. S2.