Rac1 and Rac2 regulate ROS formation required for directional migration. Neutrophil directional migration toward fMLP was determined using a Zigmond chamber. XY-plots represent the end points of migrating neutrophils with respect to the origin. (A) Rac1-null control neutrophils exhibit random migration. TAT-mediated transduction (200nM) of Rac1-null cells with wild-type Rac1 was able to rescue directionality. Transduction with TAT-Rac1-A27K also rescued directionality toward fMLP. Rac1-T17N–transduced cells behaved similarly to Rac1-null control cells. (B) Rac1/2-null double-knockout cells were transduced with equal amounts (200nM each) of TAT-tagged Rac1 wild-type or A27K and Rac2 wild-type or A27K. All combinations except Rac1-A27K/Rac2-A27K were able to rescue the directional migration defect. (C) Rac1/2 double-knockout cells were transduced with TAT-Rac1-A27K and TAT-Rac2-A27K. Subsequently, the cells were exposed to an fMLP gradient or to a combined fMLP/H₂O₂ gradient. (D) The combined results of at least 3 experiments ± SD are presented in the bar diagram. Asterisks represent significance (P < .05). XY plots depict representative results of 2-3 independent experiments.