Cdc42 is critical for neutrophil recruitment into inflamed lungs. (A) Mice reconstituted with WT or Cdc42^−/− hematopoietic cells were treated with polyI:C for Cdc42 deletion in hematopoietic system including neutrophils. Broncho-alveolar lavage (BALF) was performed 4 hours after LPS challenge in the lung. Numbers of neutrophils (*P = .0067) and macrophages (ns) recovered in brancho-alveolar lavage fluid were counted (mean ± SD, 3 independent experiments). (B) Lung function (respiratory rate) in WT or Cdc42^−/− mice challenged with saline and LPS were measured as Penh frequency by barometric plethysmograph (Buxco Research Systems; **P = .0003, t test. (C) Lung histology; lungs were harvested 24 hours after challenge and fixed, and lung histology was performed. Sections were stained with H&E, scale bar, 50 μm. Images were captured at room temperature using a Leica DMI6000 microscope at 10× objective N/A0.3 with Leica camera driven by Openlab Version 5.5.0 software. (D) Quantification of lung histology parameters as indicated (*P < .001, **P < .003). (E) Genotype of lung resident macrophages extracted from total lung assessed by WB.