The loss of Rac1 activity induces a defect in neutrophil migration into the lung alveolar spaces. Mice reconstituted with WT or Rac1^−/− hematopoietic cells were exposed to fMLP in the lung, and bronchoalveolar lavage was performed 24 hours after challenge. (A) Rac protein expression in bone marrow cells from WT or Rac1^−/−-reconstituted mice was analyzed by immunoblot using antibodies specific for Rac1 or Rac2. (B) Blood was harvested, and white blood cell (WBC) count and neutrophil (PMN) count were enumerated with a hematologic analyzer for mouse blood sample. The histogram represents the total number of cells per microliter of blood. (C) Neutrophils were isolated from peripheral blood of mice reconstituted with WT or Rac1^−/− hematopoietic cells after treatment with polyI:C. Neutrophil migration was analyzed using Boyden chamber in response to 1 μM fMLP. The result represents the number of migrated cells per field. (D) White blood cell counts and neutrophil counts at the time of killing, after fMLP challenge. (E) Total number of cells recovered in the BAL. (F) Total number of PMNs recovered in the BAL. Mean ± SEM from 3 independent experiments. (G) Mice reconstituted with WT, Rac1^−/−, and Rac1^−/− bone marrow cells expressing exogenous wtRac1 were challenged with fMLP. Cells recovered in BAL were counted by hemocytometer. Representation of individual mice; horizontal bars represent average. (H) Representative images of cytospin preparation of BAL of each group, ×400.