Blocking of GPIbα or α₂β₁ partially reduces surface coverage on collagen, but blocking only of α₂β₁ affects PS exposure. (A) Blood was treated with 12G1 Fab₂ at 40 μg/mL and 6F1 at 20 μg/mL or GFOGER-GPP at 500 μg/mL and was perfused over collagen, as described for Figure 1. Data present surface coverage of platelet deposition or OG488-labeled annexin V binding (mean ± SE, from 4-6 experiments). **P < .01, and *P < .05 compared with matched controls. (B) Blood was treated with combinations of anti-α₂ 6F1 or GFOGER and anti-β₁ 4B4 (10 μg/mL). Data (mean ± SE) present the proportion of phase- or annexin V–positive surface coverage relative to matched controls. All combinations significantly inhibited platelet responses compared with respective controls (*P < .05; n = 2) but not with each other.