Immunoprecipitation of neutrophil membranes by the patient's quinine-dependent antibodies. Donor neutrophils were surface labeled with NHS-LC-Biotin, fixed in 1% paraformaldehyde, and immunoprecipitated with normal serum (lane 2), normal serum plus quinine (lane 3), patient serum (lane 4), and patient serum plus quinine (lane 5). Immunoprecipitated neutrophil membrane proteins were analyzed by SDS-PAGE and visualized by ABC-AP Kits plus NBT/BCIP substrate. Molecular weight standards were included in lane 1.