Identification of specific protein markers of rheumatoid arthritis in synovial fluid and serum

Rheumatoid arthritis (RA) is a common articular disease characterized by chronic inf lammation, hyperproliferation of synovial cells, and bone destruction. Recently, we showed that small interfering RNA targeting CD81 (siCD81) is therapeutically effective for RA. CD81 belongs to a family of cell-surface proteins (tetraspanins) known to be up-regulated in RA synoviocytes, and siCD81 decreases the expression of synoviolin and TNF-α at the cellular level. We also previously established a highly sensitive sandwich ELISA system using monoclonal antibodies (MAbs) against CD81 by immunization with the outer membrane region of CD81 (LEL), which was overexpressed as a recombinant protein. This assay can be used to detect CD81 in synovial fluids and serum. Here, we identified several specific marker proteins and peptides for diagnosis of RA, including CD81 by using a protein chip system, 2D-gels, and western blotting. These markers can be used for early diagnosis of RA and might contribute to further effective treatment.