The loss of Rac1 activity leads to impaired neutrophil transmigration. Neutrophils were derived from WT, Rac1^−/−, or Rac2^−/− bone marrow cells. (A) Rac protein expression analyzed by immunoblot using antibodies specific for Rac1 or Rac2. (B) Neutrophil migration was analyzed using Boyden chamber assay in response to 1 μM fMLP. The result represents the number of migrated cells per field. (C-D) Neutrophil migration using transwell coated with fibrinogen. Migration was evaluated without fMLP or in uniform concentration or in a gradient of 10 μM fMLP. The histogram represents the total number of migrated neutrophils recovered from the bottom well, mean ± SD, representative experiment in triplicate from 3 independent experiments.