Surface expression of α₂β₁ remains constant on resting versus TRAP-stimulated platelets. Platelets were treated with control buffer (resting) or TRAP for 5 minutes, fixed with 0.7% PFA, and washed as described in “Materials and methods.” Platelets were then incubated with the α₂β₁ mAb BHA 2.1 (□) or control IgG₁ (▦) for 20 minutes and stained with FITC-labeled secondary goat antimouse IgG for 30 minutes. Data are shown as normalized mean fluorescence ± SEM from one experiment, representative of 2 independent experiments.