A murine monoclonal antibody specific for glycoprotein (GP)IIIa was prepared by immunization with a GPIIb- and GPIIIa-enriched Triton X-114 extract of platelet membranes. This antibody, designated AP-3, was shown by indirect immunoprecipitation to react solely with GPIIIa derived from either P1A1-positive or -negative individuals. The epitope on GPIIIa recognized by AP-3 is expressed on dissoci...

To assess the potential contribution of the cysteine-rich domain of human platelet glycoprotein (GP) IIIa to the structure of the PlA1 epitope, we used site-directed mutagenesis to substitute alanines for cysteines at key positions potentially involved in PlA1 alloantigen formation. One of these GPIIIa isoforms in which alanine replaced Cys435 reacted normally with a series of well-characterize...

Human platelet glycoproteins IIb (GPIIb) and IIIa (GPIIIa) form the subunits of the Ca(2+)-dependent heterodimer GPIIb/IIIa, which belongs to the integrin family of phylogenetically related receptors mediating a wide variety of cell-cell and cell-substratum interactions. GPIIb/IIIa plays a central role in haemostasis as a receptor for fibrinogen and other adhesive proteins at the surface of act...

The human Pena/Penb alloantigen system represents a naturally occurring polymorphism of human platelet membrane glycoprotein (GP) IIIa, and has previously been implicated in the onset of two important clinical syndromes, neonatal alloimmune thrombocytopenic purpura and posttransfusion purpura. To investigate the molecular basis of the polymorphism underlying the Pen alloantigen system, we used ...

Drug-dependent antibodies (DDAbs) can cause precipitous destruction of platelets when a patient is exposed to the drug for which they are specific. The molecular character of the epitopes recognized is poorly understood and the mechanism by which drugs promote tight binding of these antibodies to platelet glycoproteins without linking covalently to protein or antibody is not yet known. We studi...

Chronic immune thrombocytopenic purpura (ITP) is an autoimmune disorder due to antiplatelet autoantibodies, many of which are directed against platelet membrane glycoprotein (GP) IIb-IIIa or GPIb-IX. In a recent study, we described plasma autoantibodies from 13 selected ITP patients, which required the presence of the putative GPIIIa cytoplasmic region for antibody binding. Since this region ma...

Patients with human immunodeficiency virus 1-associated immunological thrombocytopenia (HIV-1-ITP) have markedly elevated platelet-bound immunoglobulin (Ig)G, IgM, and C3C4, as well as serum circulating immune complexes (CICs) composed of the same. Affinity purification of IgGs from their CICs with fixed platelets reveals high-affinity antibody (Ab) against platelet glycoprotein (GP)IIIa 49-66,...

A platelet glycoprotein (GP) IIIa epitope library was constructed by insertion of randomly cleaved GPIIIa cDNA fragments in the prokaryotic expression vector lambda gt22 and screened with purified anti-PlA1 antibodies for clones expressing a PlA1 epitope. Five independent clones were isolated and characterized by nucleotide sequencing. The smallest anti-PlA1 reactive clone obtained encoded the ...

The platelet membrane glycoprotein lIb/IlIa complex is a member of a family of a/,8 heterodimers that function as receptors for adhesive proteins. In this report we describe the structure of the human ft subunit GPIIIa deduced from an analysis of 4.0 kb of overlapping cDNA sequences isolated from a human erythroleukemia (HEL) cell cDNA expression library. A continuous open reading frame encodin...

Congenital absence of platelet glycoproteins IIb and IIIa (GPIIb and GPIIIa) results in a severe bleeding disorder characterized by defective platelet aggregation and failure of fibrinogen to bind to platelets. GPIIb is a two-chain protein containing disulfide-linked alpha and beta subunits. GPIIb and GPIIIa are present as a heterodimeric, noncovalent complex in the platelet plasma membrane and...