Background Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation at the synovial membrane. Although great progress has been made recently in exploring the etiology and pathogenesis of RA, its molecular pathological mechanism remains to be further defined and it is still a great challenge in determining the diagnosis and in choosing the appropriate therapy in early patients. This study was performed to screen candidate RA-associated serum proteins by comparative proteomics to provide research clues to early diagnosis and treatment of RA.

Methods Sera isolated from 6 RA patients and 6 healthy volunteers were pooled respectively and high-abundance proteins were depleted by Plasma 7 Multiple Affinity Removal System. The protein expression profiles between the two groups were then compared by two-dimensional gel electrophoresis (2-DE) and the proteins over/under-expressed by more than 3-fold were identified by mass spectrometry analysis. To validate the differential expression levels of the identified proteins between the two groups, ELISA was performed in two of the identified proteins in individual sera from 32 RA patients and 32 volunteers.

Results Eight proteins which over/under-expressed in sera of RA patients were identified. Among them, chain A of transthyretin (TTR) was under-expressed, while serum amyloid A protein, apolipoprotein A (ApoA)-IV, ApoA-IV precursor, haptoglobin 2, ceruloplasmin (Cp), immunoglobulin superfamily 22 and HT016 were over-expressed. ELISA test confirmed that Cp expressed remarkably higher while TTR obviously lower in RA group compared with volunteer group.

Conclusion There were 8 identified proteins differentially expressed between RA group and volunteer group, which might be candidate RA-associated proteins and might be promising diagnostic indicators or therapeutic targets for RA.