Effect of exposing collagen to plasma under flow or vWF before perfusion with whole blood at a wall shear rate of 1,500 s⁻¹. Blood containing no antibody or blood containing an anti-₂β₁ monoclonal antibody was perfused over reconstituted type I collagen (A) or over pepsin-solubilized (nonbanded) collagen from which it was derived (B) in a parallel plate flow chamber as described in the legend to Fig 2, and the flow rate was adjusted to produce a wall shear rate of 1,500 s⁻¹ at the inlet of the chamber. (A) Upper figures: The time course of platelet adhesion on reconstituted collagen was measured as described in the legend to Fig 3. The collagen substrate was pre-exposed to autologous plasma at a wall shear rate of 1,500 s⁻¹ for 5 minutes (▵) or to purified vWF under stationary conditions for 30 minutes (•) before perfusing with blood. Control blood (○) was perfused directly over reconstituted collagen without prior exposure to plasma or vWF. (A) Lower figures: After 2.5 minutes of perfusion, the total volume of platelet thrombi present in an area of 102,236 μm² was measured by confocal sectioning at 1.0-μm intervals, as described in Materials and Methods. Measurements represent the mean ± standard error of the mean of 4 separate experiments with different blood donors. The single frame images, each representing an area of 65,536 μm², depict surface coverage of platelet thrombi after 3 minutes of perfusion under the conditions indicated. (B) The time course of platelet adhesion on pepsin-solubilized (nonbanded) collagen. The collagen substrate was pre-exposed to autologous plasma at a wall shear rate of 1,500 s⁻¹ for 5 minutes (▵) or to purified vWF under stationary conditions for 30 minutes (•) before perfusing with blood. Control blood (○) was perfused directly over pepsin-solubilized (nonbanded) collagen without prior exposure to plasma or vWF. Measurements represent the mean ± standard error of the mean of 4 separate experiments with different blood donors.