SDF-1α induces a bipolar distribution of Vav and its activation at the leading edge of human PBLs. Human PBLs were allowed to adhere to 50 μg/mL fibronectin and treated or not with 10 nM (100 ng/mL) for 30 minutes, fixed, and stained for ICAM-3 (red) and either pY174 Vav or total Vav (green). Representative fields are shown. LE, leading edge; U, uropod.