Inhibitory effects of mAbs and PA autoantibodies from patients with chronic ITP on fibrinogen-binding to activated GPIIb-IIIa (GPIIb-IIIaT562N).

Biotinylated fibrinogen was added to each well containing immobilized GPIIb-IIIaT562N in the presence of various concentrations of (A) mAbs or (B) PA autoantibodies. Bound fibrinogen was measured with ELISA, and percentage fibrinogen binding was calculated as described in “Patients, materials, and methods.” (A) Open circles, OP-G2; open squares, AP2; and open triangles, MOPC21 (control IgG1). Horizontal axis represents final concentration of mAbs incubated with fibrinogen. (B) Closed circles, eluates from patients 1 and 8 showing the impaired binding to KO variant GPIIb-IIIa; open circles, eluates from patients 2 and 7 that reacted equally with KO variant and WT GPIIb-IIIa; and open squares, mean data of 3 mock control eluates. Horizontal axis represents the amount of eluate added. Experiments were run in triplicate, and data are expressed as mean ± SD of the results.