(A) Reactions of drug-dependent antibodies MA, RB, and GW with srGPIIb-IIIa in the presence (+) and absence (−) of 0.4 mmol/L quinine (MA and RB) and quinidine (GW). All three drug-dependent antibodies precipitated bands corresponding to srGPIIb and srGPIIIa in the presence of drug only. No precipitation was seen with normal plasma (NP). (B) Reactions of sulfamethoxazole-dependent antibodies BC and TB with srGPIIb-IIIa in the presence (+) and absence (−) of 0.4 mmol/L sulfamethoxazole. IgG bound to srGPIIb-IIIa was detected by modified antigen capture ELISA. No reaction was obtained with normal plasma (NP).