Differential abilities of collagen- and VWF-bound thrombi to induce neutrophil spreading under flow. Citrated whole blood was perfused over either VWF (100 μg/mL) or collagen (2 mg/mL) matrices for 5 minutes at 1800 s⁻¹ to obtain platelet thrombi. Nonadherent platelets were removed by a further 5-minute perfusion with cell-free unsupplemented Tyrode buffer at 1800 s⁻¹ followed by perfusion of isolated neutrophils (1 × 10⁶/mL) in Tyrode buffer supplemented with 1 mM CaCl₂/MgCl₂ for 5 minutes at 150 s⁻¹. Neutrophil-platelet interactions were visualized by phase-contrast microscopy and the number of neutrophils tethering in the first 30 seconds of perfusion (A), the proportion of tethering neutrophils forming stationary adhesion contacts (B), and the proportion of tethered neutrophils exhibiting spreading (C) were quantitated. Results are presented as means (± SEM; n = 4). *P < .05, **P < .01, ***P < .001.