Expression of BAFF and BAFF-R in the synovial tissue of patients with rheumatoid arthritis

Objective: The elevated expression of B- cell- activating factor belonging to the TNF family ( BAFF) is associated with systemic autoimmune disease, including rheumatoid arthritis ( RA). The present study was undertaken to determine the distribution of BAFF and its receptor BAFF- R in the cells residing in the rheumatoid synovium. Methods: The expression of BAFF and BAFF- R in synovial tissues obtained from 12 RA patients was examined by immunohistochemistry and flow cytometry. The mRNA expression of these molecules was determined by reverse transcriptase polymerase chain reaction ( RT- PCR). Soluble BAFF levels were measured with an enzyme-linked immunosorbent assay ( ELISA). Fibroblast- like synoviocytes ( FLS) purified from the RA ( RA- FLS) were co- cultured with peripheral B cells. The degree of apoptosis in the B cells was measured to assess the effects on the viability of the B cells. Results: The RA synovium showed focal or diffuse infiltration of mononuclear cells ( MNCs), and one specimen showed germinal centre ( GC)- like structures. Synovial sublining cells, but not lining cells, expressed BAFF. These sublining cells were negative for BAFF- R. BAFF and BAFF- R were expressed in B and T cells extracted from the RA synovium. Notably, RA- FLS spontaneously expressed cytoplasmic BAFF after 4 - 6 passages; however, they did not express BAFF or BAFF- R on their cell surface. RA- FLS could support the survival of B cells by preventing their apoptosis, but its effect on B cells might not be BAFF dependent. Conclusions: BAFF and BAFF- R are widely expressed in the RA synovium. The cells residing in the RA synovium might affect each other through BAFF.