The role of PF4 in survival in a murine model of LPS-induced endotoxemic shock. (A) LPS (25 mg/kg intraperitoneally) was injected and survival monitored for 24 hours, 48 hours, and 72 hours after LPS. WT (white bars; n = 7 experiments with a total of 49 animals), mPF4^−/− (gray bars; n = 5 experiments with a total of 26 animals), and hPF4⁺ (black bars; n = 4 experiments with a total of 29 animals) mice were studied. The mean (± 1 SD) is shown with statistical analysis performed using the Student t test. *P < .001 and **P < .01 compared with WT littermate controls at the same time point. (B) LPS (40 mg/kg) was injected intraperitoneally and survival monitored at 16 hours and 24 hours after LPS. WT (white bars; n = 3 experiments with a total of 17 animals), PC^+/− (light gray bars; n = 3 experiments with a total of 17 animals), PC^+/−/hPF4⁺ (dark gray bars; n = 3 experiments with a total of 14 animals), and hPF4⁺ (black bars; n = 2 experiments with a total of 10 animals) mice were studied. Statistical analysis was performed as in panel A. *P < .005 and **P < .05 relative to WT mice at the same time point, and ***P < .01 relative to PC^+/− mice at the same time point. (C) Either about 2 × 10⁸ platelets or buffer (Tyrode Hepes buffer, pH 7.2, containing 2 mg/mL BSA¹⁷ ) in 200 μL per mouse were infused intravenously immediately prior to injection of LPS (40 mg/kg intraperitoneally), and survival was noted at 16, 20, 24, and 48 hours. WT mice were infused with either buffer only (white circles; n = 29), mPF4^−/− platelets (gray triangles; n = 35), or hPF4⁺ platelets (black squares; n = 30). The mean at each time point is shown. *P < .01 and **P < .05 compared with buffer by the Fisher exact test.