Amounts of anti-GPIIb/IIIa antibodies produced in PBMC cultures before and after administration of IDEC-131/E6040. PBMCs were cultured with trypsin-digested GPIIb/IIIa, and the levels of IgG anti-GPIIb/IIIa antibodies in undiluted culture supernatants were measured by an enzyme-linked immunosorbent assay. The level of anti-GPIIb/IIIa antibodies is expressed as antibody units calculated on the basis of the standard curve obtained from serial concentrations of the mouse mAb to GPIIb/IIIa. Peripheral blood samples were analyzed at 3 different time points: day 0 (pretreatment; Pre), and days 7 and 42 after treatment (7P and 42P, respectively). A statistically significant change compared with pretreatment is indicated by < (P < .05 by repeated measures analysis of variance). In the 10 mg/kg group, ○ indicates responder and • indicates nonresponder.