title: Cross-recognition between histones and La/SSB may account for anti-DNA reactivity in SLE patients.
abstract: Antibodies to La/SSB are detected in sera of patients with primary Sjogren's syndrome (pSS) and systemic lupus erythematosus (SLE). The vast majority of anti-La/SSB positive sera contain antibodies directed towards a linear B-cell epitope of La/SSB spanning the sequence 349-364aa (pep349-364). The aim of this study was to evaluate the fluctuation of antibody levels to major B-cell epitopes of La/SSB over time and investigate for their possible crossreactions. Sequential sera from 15 SLE and 15 pSS patients, followed from 3 to 10 years were obtained. All patients with SLE were positive for anti-Ro/SSA, anti-La/SSB and anti-dsDNA antibodies and patients with pSS were positive for anti-Ro/SSA and anti-La/SSB antibodies. Sera from 30 patients with SLE without anti-La/SSB antibodies and 30 healthy individuals served as disease and negative control respectivelly. All sera tested for the presence of anti-pep349-364 antibodies, using a specific ELISA. Specific anti-pep349-364 IgG was purified from sera of SLE patients and evaluated for cross reactivity against dsDNA and histones. In all SLE sera the levels of anti-pep349-364 antibodies varied in time and fluctuated in parallel with anti dsDNA antibodies. Anti-pep349-364 IgG purified from 7 SLE patients. Five out of 7 were found to react with calf thymus DNA in ELISA. All purified (7/7) anti-pep349-364 IgG preparations reacted with histone H1 and failed to produce a positive immunofluorescence pattern in Crithidia luciliae anti-dsDNA assay which lacks histones. Competative inhibition experiments demonstrated that histone H1 could inhibit completely the binding of anti-pep349-364 IgG to pep349-364 while pep349-364 inhibited by 70% the binding of anti-pep349-364 IgG to histone H1. These findings indicate that a subgroup of SLE patients possess cross-reacting anti-histone H1 antibodies and anti-pep349-364 antibodies, which can be faulty considered as anti-dsDNA reactivity in regular ELISA techniques.
authors.affiliation: Department of Pathophysiology, School of Medicine, National University of Athens, Greece.
authors.forename: E
authors.initials: E
authors.lastname: Touloupi
authors.forename: J G
authors.initials: JG
authors.lastname: Routsias
authors.forename: A G
authors.initials: AG
authors.lastname: Tzioufas
mesh_terms: D000818:Animals; D000974:Antibodies, Antinuclear / Q000276:immunology; D001324:Autoantigens / Q000276:immunology*; D003421:Crithidia / Q000276:immunology; D003429:Cross Reactions; D004247:DNA / Q000276:immunology*; D018985:Epitopes, B-Lymphocyte / Q000276:immunology; D005455:Fluorescent Antibody Technique / Q000379:methods; D006657:Histones / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D010446:Peptide Fragments / Q000276:immunology; D011994:Recombinant Proteins / Q000276:immunology; D012261:Ribonucleoproteins / Q000276:immunology*; D012859:Sjogren's Syndrome / Q000276:immunology; D000097585:SS-B Antigen
chemical_list: D000974:Antibodies, Antinuclear; D001324:Autoantigens; D004247:DNA; D018985:Epitopes, B-Lymphocyte; D006657:Histones; D007074:Immunoglobulin G; D010446:Peptide Fragments; D011994:Recombinant Proteins; D012261:Ribonucleoproteins; D000097585:SS-B Antigen; C506261:SSB protein, human