Apoptotic platelets demonstrate reduced integrin α_IIbβ₃ activation, aggregation, and recruitment to forming thrombi under flow conditions. (A) Human whole blood was “spiked” with fluorescently labeled washed platelets treated with either vehicle (DMSO) or ABT-737 (1μM). The recruitment of vehicle or ABT-737–incubated platelets to forming thrombi was quantified as described in supplemental Methods. (i) Images are taken from 1 experiment representative of 3 independent experiments, with the mean ± SEM (n = 3) depicted in subpanel ii. (B-C) Effect of ABT-737 on integrin α_IIbβ₃ activation and platelet aggregation. Washed platelets resuspended in Tyrode buffer in the presence of BSA (5 mg/mL) were pretreated with vehicle (DMSO) or ABT-737 (1μM) for the indicated time periods, or 180 minutes. In some experiments, platelets were pretreated with Q-VD-Oph (Q-VD: 50μM) or calpeptin (CP: 100 μg/mL). (B) Integrin α_IIbβ₃ activation was measured after stimulation with ADP (25μM, 30 seconds), thrombin (0.1 or 1.0 U/mL, 5 minutes), or CRP (10 μg/mL, 5 minutes) in the presence of Oregon green–labeled fibrinogen (OG-FGN; 20 μg/mL) or FITC-PAC1, and quantified by flow cytometry, as indicated in supplemental Methods. Line graphs represent the mean ± SEM (n = 3). (C) Aggregation in response to the indicated concentration of agonist was monitored as described in supplemental Methods. Histograms represent maximal aggregation (mean ± SEM, n = 4). ns indicates not significant. **P < .01. ***P < .001.