title: Epitope specificity of anti-factor VIII antibodies from inhibitor positive acquired and congenital haemophilia A patients using synthetic peptides spanning A and C domains.
abstract: Development of antibodies (Ab) that either block the function of coagulation factor VIII (FVIII) (inhibitors) or clear it from circulation, seriously complicate the treatment of haemophilia A patients with FVIII products. Autoantibodies which develop in subjects without congenital FVIII defects, cause acquired haemophilia, a rare but life-threatening coagulopathy. Identification of the FVIII epitopes to which inhibitor Abs bind will help understanding the mechanisms of inhibitor activity, and perhaps development of new therapies. Here, we examined the FVIII peptide sequence regions recognised by anti-FVIII Ab in the plasma of six congenital and one acquired haemophilia patients with high inhibitor titers (24.4-2000 BU/ml). We used indirect ELISA and overlapping synthetic peptides, 20 residues long, spanning the sequence of the A and C FVIII domains. None of the plasma samples reacted with A1, A3 or C1 domain peptides. Six plasmas reacted with A2 and/or C2 peptides. Peptides spanning residues A2-521-690 and C2-2251-2332 were recognised most frequently and strongly. They include residues that contribute to the binding sites for activated factor IX and phosphatidyl serine/von Willebrand factor. These results suggest that anti-FVIII Abs share a pattern of antigen specificity in our panel of patients, and that exposed regions of the FVIII molecule that form functionally important binding sites elicit an intense Ab response.
authors.affiliation: Department of Immunology, School of Public Health, Tehran University of Medical Sciences, Tehran 14155, Iran.
authors.forename: Soheila
authors.initials: S
authors.lastname: Gharagozlou
authors.forename: Ramazan A
authors.initials: RA
authors.lastname: Sharifian
authors.forename: Jalal
authors.initials: J
authors.lastname: Khoshnoodi
authors.forename: Katayoon
authors.initials: K
authors.lastname: Karimi
authors.forename: Monica
authors.initials: M
authors.lastname: Milani
authors.forename: David K
authors.initials: DK
authors.lastname: Okita
authors.forename: Fazel
authors.initials: F
authors.lastname: Shokri
authors.forename: Bianca M
authors.initials: BM
authors.lastname: Conti-Fine
mesh_terms: D000328:Adult; D000918:Antibody Specificity; D001323:Autoantibodies / Q000097:blood*; D001666:Binding Sites, Antibody; D001667:Binding, Competitive; D016022:Case-Control Studies; D004797:Enzyme-Linked Immunosorbent Assay; D018604:Epitope Mapping; D000939:Epitopes; D005169:Factor VIII / Q000737:chemistry / Q000276:immunology*; D005260:Female; D006467:Hemophilia A / Q000209:etiology / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D008297:Male; D008875:Middle Aged; D010455:Peptides / Q000378:metabolism*; D017434:Protein Structure, Tertiary
chemical_list: D001323:Autoantibodies; D000939:Epitopes; D007074:Immunoglobulin G; D010455:Peptides; D005169:Factor VIII