(A) Ivermectin-treated WT mice showed improved survival compared with vehicle-treated (Veh-treated) WT mice. The survival of ivermectin-treated P2X4R^–/– and Veh-treated P2X4R^–/– mice was comparable. WT and P2X4R^–/– mice were injected with 10 mg/kg ivermectin or its vehicle and subjected to CLP. The survival of mice was monitored for 7 days. *P < 0.05, P2X4R^–/– injected with vehicle (n = 21) vs. WT injected with vehicle (n = 25); ***P < 0.001, WT injected with ivermectin (n = 20) vs. WT injected with vehicle (n = 25). (B and C) Bacterial burden was determined by counting the number of CFUs on blood agar plates after serial dilution of blood and peritoneal lavage samples. Blood and lavage fluid were collected at 16 hours after CLP. *P < 0.05 vs. Veh (Veh and 10 mg/kg ivermectin; n = 10 and 9, respectively). (D) BUN was determined from plasma of ivermectin- or Veh-treated mice 16 hours after CLP. *P < 0.05 vs. Veh; n = 10 and 9, respectively. (E and F) Ivermectin increases intracellular killing of E. coli in cultured macrophages. Peritoneal macrophages were infected with E. coli for 90 minutes and then pulsed with ATP for 5 minutes. ATP was then removed, and the macrophages were incubated with ivermectin for 30 minutes. Thereafter, the ivermectin was removed and the cells were incubated in medium containing gentamicin for another 2 hours. The cells were then lysed, and serial dilutions of intracellular content were spread onto LB agar plates. *P < 0.05 (n = 5–6); **P < 0.01 (n = 5–6). Data are expressed as mean ± SEM. All results are representatives of 3 experiments. Mortality curves were analyzed using Kaplan-Meier curve and log rank test and in the rest of the experiments one-way ANOVA followed by Mann Whitney test or two-tailed Student’s t test was used.