Activated protein C (aPC) treatments reduce lethal toxin (LT)-mediated mortality. (A) The experimental outline is illustrated. (B) The comparison of the mortality of LT-treated rats with or without aPC at 0 to 12 h following protective antigen (PA)- or LT-treatments (LT, 0.25 mg/kg single dose; aPC, 96 μg/kg/4 h; n = 15) was plotted as Kaplan-Meier curves (LT vs. LT + aPC, ** p < 0.005). The survivors in the LT + aPC group were observed for 2 mo. (C) The blood oxygen content of rats after LT (0.25 mg/kg) and LT plus aPC (LT + aPC) treatments for 4 h. Vehicle and LT data were collected from 3 experiments with 2 replicates (n = 6). The data for LT + aPC survivors and nonsurvivors were collected from 2 experiments with 2 replicates (n = 4; * p < 0.05 compared to the LT group). The nonsurvivors were those rats that survived the first 4 h of treatment, but died later (4 to 7 h). The survivors were those rats that survived the entire course of treatment (B and C; LT + aPC groups).