The loss of Rac1 activity leads to impaired RhoA activity. (A) RhoA expression in WT and Rac1^−/− PMNs by immunoblot. (B) WT and Rac1^−/− PMNs were stimulated with fMLP at the indicated time (second) and subjected to the “pull down” assay for RhoA activity which consists of using the binding domain of the RhoA effector rhotekine which binds RhoA only in the GTP-bound activated form. The amount of RhoA visualized by immunoblot represents the amount of GTP bound. Total cell lysis was analyzed for RhoA expression as loading control. The ratio between GTP-RhoA and total RhoA was analyzed by densitometry of the blot and is expressed in arbitrary units. The numbers represent fold-increased density compared with unstimulated cells. Representative blot from 3 independent experiments.