AAPP inhibits both GPVI- and integrin α₂β₁-mediated platelet adhesion to collagen. The indicated concentrations of rAAPP were incubated in 96-well plates coated with fibrillar type I collagen in the absence of Mg²⁺ (A) or with nonfibrillar type I collagen in the presence of Mg²⁺ (B) for 1 hour. After washing, washed platelet suspensions were allowed to adhere under static conditions to each well for 1 hour. After washing, adhesion platelets were quantified fluorometrically. As positive controls, washed platelet suspension were preincubated with antihuman GPVI mAb, OM-2 (1 μg/mL) (A) or anti-(human integrin α₂-subunit) mAb, 6F1 (5 μg/mL) (B). Results are representative of 3 independent experiments and expressed as the mean of triplicate reading plus or minus SEM for the indicated concentrations.