E-selectin engagement of PSGL-1 requires its cytoplasmic domain to trigger slow rolling and to activate SFKs. (A) Velocities of CD44^−/− neutrophils, OSGE-treated CD44^−/− neutrophils, or ΔCD PSGL-1/CD44^−/− neutrophils rolling on E-selectin at the indicated density with or without coimmobilized ICAM-1 (240 sites/μm²). The inset shows the expression levels of PSGL-1 on cells from the indicated genotype as measured by flow cytometry. (B) Velocities of mock- or OSGE-treated PSGL-1^−/− neutrophils rolling on E-selectin (200 sites/μm²) with or without coimmobilized ICAM-1 (240 sites/μm²). (C) OSGE-treated CD44^−/− neutrophils or ΔCD PSGL-1/CD44^−/− neutrophils were rotated on E-selectin–IgM (400 sites/μm²) in the presence or absence of EDTA or on control CD45-IgM for 5 minutes. Lysates were Western blotted with antibody that recognizes all SFKs or with anti–phospho-SFK (Y416). The data are representative of at least 3 independent experiments. *P < .01.