Immunoprecipitation of platelet membranes by the patient's quinine-dependent antibodies. Donor platelets were surface labeled with NHS-LC-Biotin and immunoprecipitated with MoAb AN51, specific for GPIb (lane 2); MoAb P2, specific for GPIIb/IIIa (lane 3); normal serum (lane 4); normal serum plus quinine (lane 5); patient serum (lane 6); and patient serum plus quinine (lane 7). Immunoprecipitated GPs were analyzed by SDS-PAGE and visualized by ABC-AP Kits plus NBT/BCIP as substrate. Molecular weight standards were included in lane 1.