Interaction of flowing platelets with a collagen or A1/collagen surface. Plasma-free blood was perfused at a shear rate of 1500 s^–1 over different coating substrates in the absence or presence of inhibitors. (A) Collagen surface, (B) A1/collagen surface, (C) A1/collagen surface, in the presence of antibody 6F1 (against the α2-I domain), and (D) A1/collagen surface, in the presence of antibody 6D1 (against GP Ibα). The photomicrographs depict the platelets tethered to the surface after 2 minutes of perfusion and represent 3 separate experiments with blood from different donors.