Inhibition of FcγRIIa-mediated HITS platelet aggregation by cross-linked anti-PECAM-1 Fab fragments. Platelet-rich plasma (3 × 10⁶ platelets/mL) was pretreated with various biotinylated Fab antibody fragments directed to CD151 (11B1) (10 μg/mL); nonbiotinylated anti-FcγRIIa (IV.3) (10 μg/mL), and anti-PECAM-1 (2BD4) (10 μg/mL) for 5 minutes prior to cross-linking with 10 μg/mL Neutravidin and stimulation with HITS-positive donor sera and 1 U/mL heparin to induce HITS-mediated platelet aggregation.