Impaired α₄ integrin– and c-Kit–induced haptotactic migration in Rac2^–/–mast cells. Mast cells from WT and Rac2-/- mice were subjected to migration assay as described in “Materials and methods.” Data are mean ± SEM from 1 of 3 representative experiments, and are expressed as the average number of migrated cells per field. At least 10 different fields were scored. *P < .05 for WT versus Rac2^-/-.