Determination of platelet autoantibody specificity by ELISA and flow cytometry.

Shown are results for ITP patient A antibody H44L4, which was judged to be specific for platelet GPIIb/IIIa because of its binding to immobilized GPIIb/IIIa (but not GPIb/IX or GPIa/IIa; panel A), its binding to wild-type platelets but not GPIIb/IIIa-deficient platelets from 3 patients with Glanzmann thrombasthenia (one of 3 examples is shown in the flow cytogram; panel B), and its immunoprecipitation of GPIIb/IIIa molecules. Antibody H68L120, an anti–blood group B antibody isolated from the same original ITP patient A library,38was used as a negative control as indicated.