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Figure 1 Translocation of CD40L to the platelet surface is not inhibited by glycoprotein IIb/IIIa receptor antagonists. The platelet-rich plasma diluted 1:5 in modified HEPES Tyrode's buffer was incubated (22°C, 10 min) with an FcRIIa blocking antibody, and then incubated (22°C, 20 min) with either buffer alone, abciximab (6.4 µg/ml), eptifibatide (1.0 µg/ml), or tirofiban (50 ng/ml). Samples were then activated (37°C, 1 h) with 50 µM isoTRAP (except the "no agonist" sample) and the phycoerythrin-conjugated CD40L-specific monoclonal antibody 24-31. Samples were then fixed with 1% formalin (22°C, 10 min), washed once, and the platelet pellet was gently resuspended in buffer containing the fluorescein isothiocyanate-conjugated CD61-specific monoclonal antibody Y2/51. Samples were analyzed for platelet surface CD40L by flow cytometry. Data are mean ± SEM, n = 4. As indicated by the asterisk, there was a significant difference between the buffer/isoTRAP sample and the buffer/no agonist sample. There were no significant differences between the buffer/isoTRAP sample and abciximab/isoTRAP, eptifibatide/isoTRAP, and tirofiban/isoTRAP samples.