In pursuit of B-cell synovial autoantigens in rheumatoid arthritis: Confirmation of citrullinated fibrinogen, detection of vimentin, and introducing carbonic anhydrase as a possible new synovial autoantigen.

We aimed to investigate potential synovial autoantigens in rheumatoid arthritis (RA) that could trigger the induction of B-cell autoantibodies. Total protein extract of synovial tissue obtained from seven RA patients was pooled and separated by 1-DE and 2-DE. The corresponding blots were probed with sera from RA (n = 30) and disease control samples (n = 30). Protein spots showing a sensitivity of > 15% were identified by MS. 1-D immunoblots revealed one protein band with a specificity in RA of 100%, a sensitivity of 43%, which was identified as fibrinogen beta chain. 2-D analysis revealed the subunits of fibrinogen, especially the beta and gamma chain, as the most prominent synovial autoantigens. We also identified vimentin, the Sa-antigen and carbonic anhydrase I as a potentially new synovial autoantigen. The protein patterns of these immunoreactive spots were observed as trains. The spots showing the highest autoimmune reactivity occurred at the acidic side of these trains and were recognized by anticitrullinated protein/peptide antibodies positive RA sera. Antimodified citrulline staining of these patterns confirmed protein citrullination. Therefore, PTMs such as citrullination due to alterations of peptidylarginine deiminase activity or generation of RA-specific epitopes, should be considered as a trigger in tolerance break.