G-CSFR^−/− mice display increased susceptibility to bronchopulmonary infection with P aeruginosa. (A) Wild-type (n = 22) and G-CSFR^−/− mice (n = 23) were challenged with a single intratracheal injection of P aeruginosa–laden beads. Kaplan-Meier estimates demonstrate significantly decreased survival in G-CSFR^−/− mice compared with wild-type mice (log rank, P = .006). Bacterial load of P aeruginosa in the lung was estimated by measuring the number of bacterial CFUs in the BALF (B) at the indicated times. The number of animals at each time point ranges from n = 4 at 24 hours to n = 21 at 48 hours. Bacterial load was also measured in whole lung homogenates (C) at 48 hours (n = 4). (D) Representative Giemsa-stained sections of lung tissue 72 hours after infection with Pseudomonas-laden beads are shown. Original magnification, × 40 (left panel) or × 200 (right panel). (E) Lungs harvested at 72 hours were sectioned and assigned a histologic score as described in “Materials and methods” (n = 4). Data represent the mean ± SEM; *P ≤ .05.