title: GPIIIa-(49-66) is a major pathophysiologically relevant antigenic determinant for anti-platelet GPIIIa of HIV-1-related immunologic thrombocytopenia.
abstract: High-affinity (Kd = 1 x 10(-9) M) anti-platelet GPIIIa has been isolated from serum immune complexes of immunologic thrombocytopenic HIV-1-infected patients (HIV-1-ITP). Affinity-purified anti-platelet antibody reacted with a recombinant GPIIIa-(1-200) and -(1-66) fusion peptide and with an 18-mer GPIIIa-(49-66) peptide but not with seven other GPIIIa peptides spanning the length of GPIIIa. Most of the anti-platelet antibody ( approximately 85%) could be adsorbed to and eluted from a GPIIIa-(49-66) affinity column. Binding of antibody to platelets could be inhibited by GPIIIa-(49-66) or an equimolar peptide-albumin conjugate (IC50 = 2 microM). Sera from 7 control subjects and 10 classic autoimmune thrombocytopenic patients gave background reactivity with GPIIIa-(49-66). HIV-1-ITP sera from 16 patients reacted with a mean OD 6-fold greater than background (range, 4- to 9-fold). Serum anti-GPIIIa-(49-66) concentration correlated inversely with platelet count, R2 = 0.51, n = 31, P < 0. 0001. Because mouse platelet GPIIIa-(49-66) has 83% homology with human GPIIIa and mouse monocytes contain Fc receptors for the human IgG1-kappa/lambda antibody, we determined the in vivo effect of human anti-GPIIIa on mouse platelets. Affinity-purified antibody, 25-50 microg given i.p., resulted in a precipitous drop in platelet count to 30% of baseline, with nadir at 4 hr and return to normal in 36 hr. No effect was noted with control IgG. Acute thrombocytopenia could be prevented or reversed by the injection of the GPIIIa-(49-66) albumin conjugate at zero time or 2 hr after antibody, respectively, but not with a scrambled peptide-albumin conjugate. Thus HIV-1-ITP patients have high-affinity anti-platelet GPIIIa against a major antigenic determinant, GPIIIa-(49-66), which correlates inversely with platelet count and induces thrombocytopenia in mice.
authors.affiliation: Department of Pediatrics, New York University Medical Center, 550 First Avenue, New York, NY 10016, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Nardi
authors.forename: L X
authors.initials: LX
authors.lastname: Liu
authors.forename: S
authors.initials: S
authors.lastname: Karpatkin
mesh_terms: D000818:Animals; D000906:Antibodies / Q000097:blood*; D015703:Antigens, CD / Q000276:immunology*; D001792:Blood Platelets / Q000276:immunology*; D018604:Epitope Mapping; D005260:Female; D015658:HIV Infections / Q000097:blood / Q000276:immunology* / Q000503:physiopathology; D015497:HIV-1; D006801:Humans; D016056:Immunodominant Epitopes / Q000276:immunology*; D039661:Integrin beta3; D008297:Male; D051379:Mice; D010446:Peptide Fragments / Q000276:immunology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins / Q000276:immunology*; D013921:Thrombocytopenia / Q000276:immunology* / Q000503:physiopathology
chemical_list: D000906:Antibodies; D015703:Antigens, CD; D016056:Immunodominant Epitopes; D039661:Integrin beta3; D010446:Peptide Fragments; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; C106958:platelet glycoprotein (GP)IIIa 49-66