title: Reactivity of autoantibodies from chronic ITP patients with recombinant glycoprotein IIIa peptides.
abstract: Chronic immune thrombocytopenia is an autoimmune disorder characterized by destructive thrombocytopenia due to the formation of autoantibodies against platelet-associated antigens. Most antiplatelet autoantibodies react with either the platelet glycoprotein IIb/IIIa or Ib/IX complex, whereas some plasma autoantibodies react with glycoprotein IIIa. Previous studies from our laboratory suggested that most platelet-associated autoantibodies to platelet GPIIb/IIIa, which bind to the intact complex, bind much less avidly to the EDTA-dissociated complex, suggesting that the epitopes were complex-dependent. To evaluate this further we have studied the binding of platelet-associated autoantibody and plasma auto- and alloantibody eluates to large recombinant GPIIIa peptides: peptide 1 (GPIIIa Gly1-Val200); peptide 2 (GPIIIa Arg150-Glu400); peptide 3 (GPIIIa Lys350-Asp550); peptide 4 (GPIIIa Asn450-Val700) and peptide 5 (GPIIIa Trp715-Thr762, cytoplasmic fragment). Of the 33 platelet-associated antibody eluates tested, all bound avidly to the GPIIb/IIIa complex, but only one showed significant binding (>3 SD above control values) to one of the immobilized peptides (peptide 3). Conversely, antibodies known to bind to specific regions of GPIIIa (murine monoclonal antibody, anti-LIBS2; plasma autoantibody against the GPIIIa cytoplasmic fragment and anti-P1A1 antibody) all bound avidly to the GPIIIa peptide containing the appropriate epitope. Based on these and our previous results, we conclude that platelet-associated antibodies from chronic ITP patients rarely bind to epitopes localized to GPIIIa alone.
authors.affiliation: Department of Molecular and Experimental Medicine, Scripps Research Institute, LaJolla, California 92037, USA.
authors.forename: R D
authors.initials: RD
authors.lastname: Bowditch
authors.forename: P
authors.initials: P
authors.lastname: Tani
authors.forename: R
authors.initials: R
authors.lastname: McMillan
mesh_terms: D001323:Autoantibodies / Q000276:immunology*; D001327:Autoimmune Diseases / Q000276:immunology*; D001483:Base Sequence; D001792:Blood Platelets / Q000276:immunology; D002908:Chronic Disease; D000939:Epitopes / Q000276:immunology; D006801:Humans; D008969:Molecular Sequence Data; D010980:Platelet Membrane Glycoproteins / Q000276:immunology*; D016133:Polymerase Chain Reaction; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology
chemical_list: D001323:Autoantibodies; D000939:Epitopes; D010980:Platelet Membrane Glycoproteins; D011994:Recombinant Proteins