Strong TCR stimulation in the late phase of priming antagonizes division. (A and B) LifeAct-GFP⁺ or GFP⁺ OT-I CD8⁺ T cells were adoptively transferred, and recipients were stimulated by an i.v. injection of OVAp. Intravital imaging of the popliteal lymph node was performed at 30 or 48 h. OVAp was reinjected during the imaging experiment. Mitosis events were analyzed before or immediately after OVAp reinjection. (A) Representative images before or after OVAp reinjection illustrating that T cell divisions are reduced upon stimulation. Bar, 30 µm. (B) Quantification of T cell division before and after OVAp reinjection. Each line represents one independent video, and each square corresponds to 1 min of imaging. Red squares indicate the occurrence of a mitotic event in the imaging field. (C) The same experiment was performed in the presence of anti–PD-1 treatment or isotype control at 48 h. In these conditions also, OVAp inhibited T cell mitosis. (D and E) Compilation of the number of T cell division per hour in the imaging field before and after OVAp reinjection for the indicated conditions and time points. Each pair of dots corresponds to one imaging area. Data are pooled from three (D) or two (E) independent experiments. Significance testing was performed by using a paired t test. *, P < 0.05; ***, P < 0.001.