title: Epitope spreading to citrullinated antigens in mouse models of autoimmune arthritis and demyelination.
abstract: BACKGROUND
  Anti-citrullinated protein antibodies have a diagnostic role in rheumatoid arthritis (RA); however, little is known about their origins and contribution to pathogenesis. Citrullination is the post-translational conversion of arginine to citrulline by peptidyl arginine deiminase, and increased citrullination of proteins is observed in the joint tissue in RA and in brain tissue in multiple sclerosis (MS).
  
  
  METHODS
  We applied synovial and myelin protein arrays to examine epitope spreading of B cell responses to citrullinated epitopes in both the collagen-induced arthritis (CIA) model for RA and the experimental autoimmune encephalomyelitis (EAE) model for MS. Synovial and myelin protein arrays contain a spectrum of proteins and peptides, including native and citrullinated forms, representing candidate autoantigens in RA and MS, respectively. We applied these arrays to characterise the specificity of autoantibodies in serial serum samples derived from mice with acute and chronic stages of CIA and EAE.
  
  
  RESULTS
  In samples from pre-disease CIA and acute-disease EAE, we observed autoantibody targeting of the immunising antigen and responses to a limited set of citrullinated epitopes. Over the course of diseases, the autoantibody responses expanded to target multiple citrullinated epitopes in both CIA and EAE. Using immunoblotting and mass spectrometry analysis, we identified citrullination of multiple polypeptides in CIA joint and EAE brain tissue that have not previously been described as citrullinated.
  
  
  CONCLUSIONS
  Our results suggest that anti-citrulline antibody responses develop in the early stages of CIA and EAE, and that autoimmune inflammation results in citrullination of joint proteins in CIA and brain proteins in EAE, thereby creating neoantigens that become additional targets in epitope spreading of autoimmune responses.
authors.affiliation: Department of Medicine, Division of Immunology and Rheumatology, CCSR 4135, 269 Campus Dr, Stanford University School of Medicine, Stanford, CA, USA. bkidd@u.washington.edu
authors.forename: Brian A
authors.initials: BA
authors.lastname: Kidd
authors.forename: Peggy P
authors.initials: PP
authors.lastname: Ho
authors.forename: Orr
authors.initials: O
authors.lastname: Sharpe
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Zhao
authors.forename: Beren H
authors.initials: BH
authors.lastname: Tomooka
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Kanter
authors.forename: Lawrence
authors.initials: L
authors.lastname: Steinman
authors.forename: William H
authors.initials: WH
authors.lastname: Robinson
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology* / Q000378:metabolism; D015153:Blotting, Western; D002956:Citrulline / Q000276:immunology*; D003711:Demyelinating Diseases / Q000276:immunology; D004681:Encephalomyelitis, Autoimmune, Experimental / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D018985:Epitopes, B-Lymphocyte / Q000276:immunology*; D013058:Mass Spectrometry; D051379:Mice; D040081:Protein Array Analysis
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D018985:Epitopes, B-Lymphocyte; D002956:Citrulline