Binding of rifampicin-dependent antibody to platelet surface glycoproteins.

MAIPA assay, an antigen-capture ELISA, was performed using SZ21, SZ22, and AP2, anti-GPIIb-IIIa mAbs, to capture the GPIIb-IIa complex or AK2 (an anti-GPIbα mAb) or FMC25 (a non–cross-blocking anti-GPIX mAb) to capture the GPIb-IX complex. The studies were performed in the presence and absence of rifampicin with patient serum (Pt) or the control (AB serum). Samples were assayed in the presence or absence of rifampicin. Binding was not observed with the AB serum in the presence or absence of rifampicin with any of the mAbs. The patient serum did not bind in the absence of rifampicin. In the presence of rifampicin, the patient serum gave a positive result in the presence of GPIbα-specific mAb AK2 and GPIX-specific mAb FMC25. A negative result was observed with GPIIb-IIIa mAbs SZ 1, SZ22 (data not shown), and AP2. These data suggest that the antibody(ies) in the patient serum reacted with GPIb-IX complex but not with the GPIIb-IIIa complex.