Flow cytometric measurement of antibody binding from chimpanzee A-264 and control chimpanzee plasma alternatively using chimpanzee A-264 and control chimpanzee platelets (A and B) and human platelets (C) in the presence of 10 μmol/L drug. (A) depicts the histograms from flow cytometric measurements of DDAb binding in the presence (+) and in the absence (−) of A2-L. Data in (B) represent the mean ± SD from three measurements. Data in (C) using A2-L and A1-L represent the mean ± SD from measurements using platelets of 45 human subjects; for other compounds, data represent the mean ± SD from measurements using platelets of three human subjects. Binding of DDAbs is plotted as relative fluorescence of an FITC-labeled secondary antibody. The right two sets of bars in (C) represent results with human platelets pretreated at 37°C for 1 hour with 10 mmol/L EDTA. A2-R (Kd, 0.45 nmol/L) and A1-R (Kd, 0.28 nmol/L) are R-isomers of A2-L and A1-L, respectively.