PD-1 KO mice exhibit systemically increased vascular permeability. (A) EB was injected i.v. to WT and PD-1 KO mice on day 6 after 10⁶ pfu LCMV docile infection and EB extravasation was analyzed in the kidney, liver, lung, and brain. The mean EB concentration in organs of WT mice was normalized to 1. Values in PD-1 KO mice were calculated accordingly. WT, n = 10 mice; KO, n = 5–6 mice. Means ± SEM from three pooled experiments are shown. (B) Photos of PBS-perfused lung lobes from WT and PD-1 KO mice were taken after EB injection on day 6 after infection. Photos from representative mice from one of two experiments are shown. (C) TAT plasma concentrations were determined in naive WT and PD-1 KO mice and infected WT, αPD-L1–treated WT, and PD-1 KO mice on day 6 p.i. Infected, n = 3–4 mice per group; naive, n = 1 mouse per group. Means ± SEM from one representative of two experiments are shown. (D) Total numbers of blood platelets were determined in WT and PD-1 KO mice on day 6 after infection. n = 2–4 mice per group. Means ± SEM from one representative of two experiments are shown. (E) EB extravasation was determined in the kidney, liver, and lung of infected WT, PD-1 KO, and αIL-6R + αTNF–treated PD-1 KO mice on day 6 after systemic infection. n = 6–8 mice per group. Means ± SEM from two pooled experiments are shown. (F) EB extravasation was analyzed in the kidney, liver, and lung of untreated WT and PKOB mice and αPD-L1–treated WT and PKOB mice on day 6 p.i. n = 6–8 mice per group. Means ± SEM from two pooled experiments are shown. n.s.: not significant. (G) EB extravasation was analyzed in the lungs of 2.5 × 10⁴ PD-1^−/− P14 cell-transferred WT→WT and WT→H-2D^b KO chimeric mice on day 6 p.i. WT→WT, n = 7 mice per group; WT→H-2D^b KO, n = 12 mice per group. Means ± SEM from two pooled experiments are shown. *, P < 0.05; **, P < 0.01 (unpaired two-tailed Student’s t test).