Immunoblot of srGPIIb precipitated from day-4 culture supernatant by MoAbs Tab (anti-GPIIb H), AP3 (anti-GPIIIa), and AP2 and 7E3 (anti-GPIIb-IIIa complex) in the absence (lanes 1, 3, 5, and 7) and presence (lanes 2, 4, 6, and 8) of 10 mmol/L EDTA. All four MoAbs precipitated srGPIIb from untreated culture medium. After the addition of EDTA to dissociate srGPIIb-IIIa, precipitation was achieved only with Tab.