title: Heterogeneity of autoantibodies to factor VIII: differences in specificity for apparently distinct antigenic determinants of factor VIII coagulant protein.
abstract: The interference of antibodies to factor VIII coagulant protein (VIII:C) of 9 nonhemophilic patients with the binding to factor VIII coagulant antigen (VIII:CAg) of a reference hemophilic 125I-Fab' reagent, used in a liquid phase VIII:CAg assay, was studied. The binding competition was estimated from immunoradiometric assay (IRMA) dose-response slope of VIII:CAg present in patient plasma, interference of antibodies with the 125I-Fab' binding to VIII:CAg in normal plasma, and the displacement of antibody from the complexes with VIII:CAg by the 125I Fab'. Antibody populations from three patients were studied in detail; in the VIII:CAg assay, two of them interfered with the 125I-Fab' binding, and one did not (patient 1). The formation of stable complexes between antibodies of each patient and VIII:CAg was demonstrated by protein-A-Sepharose adsorption. The 125I-Fab' binding to VIII:CAg-anti-VIII:CAg IgG complexes indicated that patient 1 antibodies and the 125I-Fab' recognized different antigenic determinants, whereas the other two patient antibodies and 125I-Fab' recognized closely related or identical VIII:CAg determinants. These results demonstrate an apparently selective recognition of at least two distinct VIII:CAg determinants by naturally occurring antibodies, suggesting a possibility of a wider use of these antibodies in studies of the structure and function of factor VIII.
mesh_terms: D000936:Antigen-Antibody Complex / Q000276:immunology; D000941:Antigens / Q000276:immunology*; D001323:Autoantibodies / Q000145:classification / Q000276:immunology*; D004306:Dose-Response Relationship, Immunologic; D000939:Epitopes / Q000032:analysis* / Q000276:immunology; D005169:Factor VIII / Q000276:immunology*; D006467:Hemophilia A / Q000276:immunology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D014842:von Willebrand Diseases / Q000276:immunology
chemical_list: D000936:Antigen-Antibody Complex; D000941:Antigens; D001323:Autoantibodies; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments; D005169:Factor VIII