title: Sequestration of anti-platelet GPIIIa antibody in rheumatoid factor immune complexes of human immunodeficiency virus 1 thrombocytopenic patients.
abstract: Human immunodeficiency virus 1-related idiopathic thrombocytopenic purpura (HIV-1-ITP) patients have a 4-fold increased percentage of CD5+ B cells and a 4.8-fold increased percentage of serum immune complexes precipitated by polyethylene glycol (PEG-ICs) compared to control subjects, as reported previously. Since CD5+ B cells produce predominantly IgM rheumatoid factor (RF) vs. Fc of IgG and PEG-ICs contain high levels of IgM, we looked for the presence of RF in the immune complexes of HIV-1-ITP patients. PEG-ICs were adsorbed to protein A and dissociated with acid, and IgM and IgG were purified by gel filtration and affinity chromatography. Solid-phase ELISA was used to measure antibody specificity vs. platelets, Fc, and HIV-1 gp120, p24, and CD4. Dissociated IgG antibody reacted with platelets, HIV-1 gp120, p24, and CD4, but not with Fc. Serum IgG did not react with platelets or Fc but did react with HIV-1 gp120, p24, and CD4. Both PEG-IC IgM and serum IgM reacted with Fc as well as the other four antigens. Control IgM and IgG were unreactive. Isolated IgM from PEG-ICs relocated approximately 50% of the IgG preincubated with IgM to the Vo region of a G200 gel-filtration column. Anti-platelet IgG but not IgM could be affinity-purified from fixed platelets. Both F(ab')2 fragments of anti-platelet IgG and the total PEG-IC bound to platelets in a saturation-dependent manner. F(ab')2 of anti-platelet IgG inhibited 50% binding of PEG-IC to platelets at an F(ab')2/complex ratio of 3:1 (wt/wt). Scatchard analysis revealed two classes of binding sites: high-affinity Kd values of 0.8-1.8 nM and lower-affinity Kd values of 6.6-12.3 nM with respective numbers of binding sites of 44,000-57,000 and 122,000-256,000 (n = 4). Anti-platelet IgG of 6/6 patients precipitated GPIIIa from platelet lysates of surface 125I-labeled platelets. Platelet count correlated inversely with anti-platelet IgG (r = -0.73; P < 0.01; n = 27). Thus, PEG-ICs of HIV-1-ITP patients contain IgM RF, which sequesters serum anti-platelet IgG containing anti-GPIIIa. Anti-platelet IgG contributes to binding of immune complexes to platelets and correlates with thrombocytopenia.
authors.affiliation: Department of Medicine, New York University Medical School, NY 10016.
authors.forename: S
authors.initials: S
authors.lastname: Karpatkin
authors.forename: M A
authors.initials: MA
authors.lastname: Nardi
authors.forename: K B
authors.initials: KB
authors.lastname: Hymes
mesh_terms: D000936:Antigen-Antibody Complex / Q000097:blood*; D001323:Autoantibodies / Q000097:blood*; D001665:Binding Sites; D001792:Blood Platelets / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D006679:HIV Seropositivity / Q000097:blood / Q000150:complications / Q000276:immunology*; D015497:HIV-1; D018451:Homosexuality, Male; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000097:blood; D007141:Immunoglobulin Fc Fragments / Q000097:blood; D007074:Immunoglobulin G / Q000097:blood* / Q000302:isolation & purification; D007075:Immunoglobulin M / Q000097:blood* / Q000302:isolation & purification; D007700:Kinetics; D008297:Male; D010980:Platelet Membrane Glycoproteins / Q000276:immunology*; D011092:Polyethylene Glycols; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000097:blood / Q000150:complications / Q000276:immunology*; D012217:Rheumatoid Factor / Q000097:blood*; D015819:Substance Abuse, Intravenous
chemical_list: D000936:Antigen-Antibody Complex; D001323:Autoantibodies; D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D010980:Platelet Membrane Glycoproteins; D011092:Polyethylene Glycols; D012217:Rheumatoid Factor