Application of flow cytometry and the activation-dependent monoclonal antibody PAC-1 to the study of αIIbβ3 conformational changes and ligand binding. (A) Platelets were identified and differentiated from red and white blood cells by their characteristic forward and side-angle light scatter profiles. (B) Platelets were stimulated with ADP and epinephrine or incubated with PGI₂ to block activation. The fluorescence histogram depicts biotin-PAC-1 binding to the platelets detected by phycoerythrin-streptavidin. Reprinted from Shattil et al. Blood. 1987;70:307.⁵⁹