Soluble fibrinogen binding to cultured MKs is specific for GPIIb-IIIa. In each experiment, cultured cells were incubated with PE-GPIb antibody and FITC-FGN in the presence (shaded histograms) and absence (unshaded histograms) of TRAP and with or without the indicated blocking antibody. FITC fluorescence (FL1) histograms were generated from the MK population. (A) No blocking antibody. (B) KGD heptapeptide (Integrilin). (C) RGDS peptide. (D) 10E5 antibody. (E) LM609 antibody. (F) Nonspecific mouse monoclonal IgG. Data are representative of 3 experiments performed.