Rac GTPases required for chemokine-induced cytoskeletal reorganization. (A) Mean ± SEM F-actin in CD4⁺ T cells of the indicated genotypes stimulated with CXCL12, CCL19, or CCL21 (200 ng/mL) or not stimulated. All F-actin measurements were normalized to F-actin content of unstimulated WT T cells. Data are from 4 independent experiments. (B) Mean ± SEM pERM in CD4⁺ T cells of the indicated genotypes stimulated with CCL21 (500 ng/mL) for the indicated times. All pERM measurements were normalized to WT T cells at time = 0 seconds. Data are from 3 independent experiments. *P < .05; **P < .01; ***P < .001.