title: An immunodominant La/SSB autoantibody proteome derives from public clonotypes.
abstract: The La/SSB autoantigen is a major target of long-term humoral autoimmunity in primary Sjögren's Syndrome (SS) and systemic lupus erythematosus. A majority of patients with linked anti-Ro60/Ro52/La responses target an NH2-terminal epitope designated LaA that is expressed on Ro/La ribonucleoprotein complexes and the surface membrane of apoptotic cells. In this study, we used high-resolution Orbitrap mass spectrometry to determine the clonality, isotype and V-region sequences of LaA-specific autoantibodies in seven patients with primary SS. Anti-LaA immunoglobulin (Ig)Gs purified from polyclonal sera by epitope-specific affinity chromatography were analysed by combined database and de-novo mass spectrometric sequencing. Autoantibody responses comprised two heavily mutated IgG1 kappa-restricted monoclonal species that were shared (public) across unrelated patients; one clonotype was specified by an IGHV3-30 heavy chain paired with IGKV3-15 light chain and the second by an IGHV3-43/IGKV3-20 pairing. Shared amino acid replacement mutations were also seen within heavy and light chain complementarity-determining regions, consistent with a common breach of B cell tolerance followed by antigen-driven clonal selection. The discovery of public clonotypic autoantibodies directed against an immunodominant epitope on La, taken together with recent findings for the linked Ro52 and Ro60 autoantigens, supports a model of systemic autoimmunity in which humoral responses against protein-RNA complexes are mediated by public sets of autoreactive B cell clonotypes.
authors.affiliation: Department of Immunology, Flinders Medical Centre, Flinders University, Adelaide, SA, Australia.
authors.forename: L A
authors.initials: LA
authors.lastname: Thurgood
authors.forename: G
authors.initials: G
authors.lastname: Arentz
authors.forename: R
authors.initials: R
authors.lastname: Lindop
authors.forename: M W
authors.initials: MW
authors.lastname: Jackson
authors.forename: A F
authors.initials: AF
authors.lastname: Whyte
authors.forename: A D
authors.initials: AD
authors.lastname: Colella
authors.forename: T K
authors.initials: TK
authors.lastname: Chataway
authors.forename: T P
authors.initials: TP
authors.lastname: Gordon
mesh_terms: D000293:Adolescent; D000328:Adult; D001323:Autoantibodies / Q000276:immunology* / Q000302:isolation & purification; D001324:Autoantigens / Q000276:immunology / Q000378:metabolism*; D001402:B-Lymphocytes / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D002846:Chromatography, Affinity; D060966:Clonal Selection, Antigen-Mediated; D002999:Clone Cells; D005260:Female; D006801:Humans; D007108:Immune Tolerance; D056724:Immunity, Humoral; D016056:Immunodominant Epitopes / Q000276:immunology / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D040901:Proteomics; D012261:Ribonucleoproteins / Q000276:immunology / Q000378:metabolism*; D012859:Sjogren's Syndrome / Q000276:immunology*; D055815:Young Adult; D000097585:SS-B Antigen; D000099207:SS-A Antigen
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D016056:Immunodominant Epitopes; D012261:Ribonucleoproteins; D000097585:SS-B Antigen; D000099207:SS-A Antigen
keywords: La/SSB; mass spectrometry; primary Sjögrens syndrome; public clonotypes