Measurement of the αIIbβ3 content of patient platelets using flow cytometry. Comparison of αIIb-β3 expression on the surface of patient and control platelets using the αIIb-specific MoAb B1B5, the αIIbβ3 heterodimer-specific MoAb A2A9, the activation-dependent anti-αIIbβ3 MoAb PAC-1, and the GP1b-complex specific MoAb AP-1. The data in the figure are expressed as the percentage of antibody binding to patient versus control platelets. Measurements of PAC-1 binding were made after stimulating platelets with 0.2 μmol/L phorbol myristate acetate. (▪) Control; (▨) patient.