title: Candidate autoantigens identified by mass spectrometry in early rheumatoid arthritis are chaperones and citrullinated glycolytic enzymes.
abstract: BACKGROUND
  The aim of our study was to identify new early rheumatoid arthritis (RA) autoantibodies.
  
  
  METHODS
  Sera obtained from 110 early untreated RA patients (<6 months) were analyzed by western blot using HL-60 cell extract, separated on one-dimensional and two-dimensional gel electrophoresis (1-DE, 2-DE). Sera from 50 healthy blood donors and 20 patients with non-RA rheumatisms were used as controls for 1-DE and 2-DE, respectively. The immunoreactive proteins were identified by MALDI-TOF mass spectrometric analysis and the presence of potential sites of citrullination in each of these proteins was evaluated. FT-ICR mass spectrometry was used to verify experimentally the effect of citrullination upon the mass profile observed by MALDI-TOF analysis.
  
  
  RESULTS
  The 110 1-DE patterns allowed detection of 10 recurrent immunoreactive bands of 33, 39, 43, 46, 51, 54, 58, 62, 67 and 70 kDa, which were further characterized by 2-DE and proteomic analysis. Six proteins were already described RA antigens: heterogeneous nuclear ribonucleoprotein A2/B1, aldolase, alpha-enolase, calreticulin, 60 kDa heat shock protein (HSP60) and BiP. Phosphoglycerate kinase 1 (PGK1), stress-induced phosphoprotein 1 and the far upstream element-binding proteins (FUSE-BP) 1 and 2 were identified as new antigens. Post-translational protein modifications were analyzed and potentially deiminated peptides were found on aldolase, alpha-enolase, PGK1, calreticulin, HSP60 and the FUSE-BPs. We compared the reactivity of RA sera with citrullinated and noncitrullinated alpha-enolase and FUSE-BP linear peptides, and showed that antigenicity of the FUSE-BP peptide was highly dependent on citrullination. Interestingly, the anti-cyclic citrullinated peptide antibody (anti-CCP2) status in RA serum at inclusion was not correlated to the reactivity directed against FUSE-BP citrullinated peptide.
  
  
  CONCLUSIONS
  Two categories of antigens, enzymes of the glycolytic family and molecular chaperones are also targeted by the early untreated RA autoantibody response. For some of them, and notably the FUSE-BPs, citrullination is involved in the immunological tolerance breakdown observed earlier in RA patients. Autoantibodies recognizing a citrullinated peptide from FUSE-BP may enhance the sensibility for RA of the currently available anti-CCP2 test.
authors.affiliation: Department of Rheumatology and Inserm Unit 905, IFRMP 23, Institute for Biomedical Research, University of Rouen, Rouen University Hospital, Rouen 76031 cedex, France. goebvince@yahoo.fr
authors.forename: Vincent
authors.initials: V
authors.lastname: Goëb
authors.forename: Marlène
authors.initials: M
authors.lastname: Thomas-L'Otellier
authors.forename: Romain
authors.initials: R
authors.lastname: Daveau
authors.forename: Roland
authors.initials: R
authors.lastname: Charlionet
authors.forename: Patrice
authors.initials: P
authors.lastname: Fardellone
authors.forename: Xavier
authors.initials: X
authors.lastname: Le Loët
authors.forename: François
authors.initials: F
authors.lastname: Tron
authors.forename: Danièle
authors.initials: D
authors.lastname: Gilbert
authors.forename: Olivier
authors.initials: O
authors.lastname: Vittecoq
mesh_terms: D001172:Arthritis, Rheumatoid / Q000276:immunology*; D001323:Autoantibodies / Q000032:analysis / Q000097:blood / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology*; D015415:Biomarkers / Q000097:blood; D015153:Blotting, Western; D020552:Comet Assay; D015180:Electrophoresis, Gel, Two-Dimensional; D006801:Humans; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D015415:Biomarkers