Research article

Candidate autoantigens identified by mass spectrometry in early rheumatoid arthritis are chaperones and citrullinated glycolytic enzymes

Vincent Goëb¹ , Marlène Thomas-L'Otellier² , Romain Daveau² , Roland Charlionet² , Patrice Fardellone³ , Xavier Le Loët¹ , François Tron² , Danièle Gilbert² and Olivier Vittecoq¹

¹  Department of Rheumatology and Inserm Unit 905, IFRMP 23, Institute for Biomedical Research, University of Rouen, Rouen University Hospital, Rouen 76031 cedex, France

²  Immunology Laboratory and Inserm Unit 905, IFRMP 23, Institute for Biomedical Research, University of Rouen, Rouen University Hospital, Rouen, 76031 cedex, France

³  Rheumatology Department, Amiens University Hospital, Amiens 80054, France

author email corresponding author email

Arthritis Research & Therapy 2009, 11:R38doi:10.1186/ar2644

Published:	10 March 2009

Abstract

Introduction

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, α-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, α-enolase, PGK1, calreticulin, HSP60 and the FUSE-BPs. We compared the reactivity of RA sera with citrullinated and noncitrullinated α-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.