Antibody binding to platelet antigens in acute and chronic idiopathic thrombocytopenic purpura: a platelet membrane ELISA for the detection of antiplatelet antibodies in serum.

A solid-phase platelet membrane enzyme linked immunosorbent assay (ELISA) was developed for the detection of circulating platelet binding IgG in serum. 18 out of 28 (64%) sera from patients with chronic idiopathic thrombocytopenic purpura (ITP) and 10 out of 21 (48%) sera from patients with acute ITP contained more platelet binding IgG than the mean +2 s.d. of 25 normal control sera. IgG-F(ab')2 fragments from two anti-PlA1 sera, from six out of seven positive chronic ITP sera and from four out of eight positive acute ITP sera bound to normal platelet membrane. When IgG-F(ab')2 preparations, which reacted with normal membrane, were tested against glycoprotein IIb-IIIa-deficient platelet membrane obtained from a patient with Glanzmann's thrombasthaenia, the reactions of F(ab')2 fragments from two anti-PlA1 sera, from three out of four acute ITP sera and from four out of six chronic ITP sera were reduced to control levels. It is concluded that IgG-F(ab')2 antibody binding to platelet specific antigens, some of which are associated with the glycoprotein IIb-IIIa complex, can be demonstrated not only in anti-PlA1 sera or sera from chronic ITP patients but also in sera from some patients with acute ITP. Moreover, when the IgG binding to platelet membrane of whole sera is tested, positive results may sometimes be ascribed to the presence of immune complexes.