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 β chain. 2-D analysis revealed the subunits of 
fibrinogen, especially the β and γ 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.