PA SN induces lung injury after antibody-mediated platelet depletion of WT mice, and PA SN-induced injury can be attenuated by partial reconstitution of platelet counts in natively thrombocytopenic Mpl^−/−mice. WT mice were administered anti-GP1bα or control antibody 24 hours prior to IT PA SN, and necropsy was performed at 20 hours with peripheral blood platelet counts (10⁹/L) (A). At necropsy 20 hours after IT PA SN inoculation, gross appearance of BAL fluid (B), BAL OD₅₄₀ measurements (C), BAL protein concentrations (mg/mL) (D), BAL IgM concentrations (ng/mL) (E), and BAL neutrophil counts/mL (F) are shown (n = 6 mice/group; 2 deaths occurred in the anti-GP1bα group prior to the 20-hour time point). In separate experiments, vehicle or 10⁹ platelets from WT mice were transfused into Mpl^−/− mice 1 hour following IT PA SN administration. Blood platelet counts (10⁹/L) (G), gross appearance of BAL fluid (H), and BAL OD₅₄₀ measurements (I) were obtained 20 hours post-PA infection. Each tube or point represents a single mouse (n = 5 for vehicle, n = 7 for the WT platelet group; peripheral blood was not successfully obtained from 1 mouse in the vehicle group), and the group median is displayed. Statistical comparison by Mann-Whitney U test. *P < .05 and **P < .01.