Flow cytometric analysis of surface-expressed allelic forms of GPIIb-IIIa. (A) Binding of LIBS antibody D3 to Pen^a (Arg₁₄₃)-transfected CHO cells. D3 binding was measured in the presence or absence of RGDW or RGEW peptides. Whereas RGDW peptides increased the binding of D3 to transfected CHO cells, RGEW did not. As a control, binding of AP3 to the cells was also measured. Neither RGDW nor RGEW affected the binding of AP3. (B) Binding of LIBS antibody D3 to Pen^b(Gln₁₄₃)-transfected CHO cells. D3 binding to Pen^b-transfected CHO cells was increased in the presence of RGDW peptides. AP3 binding was not affected by RGDW peptides. The number above each histogram represents the mean fluorescence intensity. (C) Binding of activation-dependent antibody Pl-55. Transfected CHO cells were incubated with FITC-labeled Pl-55 in the presence of AP3 or D3 (200 μg/mL) for 30 minutes. The samples were diluted with PBS and analyzed by a FACScan. Nonspecific binding of the antibody was defined in the presence of 1 mmol/L RGD peptides. D3 increased the binding of Pl-55 to both Pen^a- and Pen^b-transfected CHO cells. Pl-55 binding was inhibited by 1 mmol/L RGDW peptides.