Expression of Fas antigen and Fas ligand in the rheumatoid synovial tissue.

To understand the role of apoptosis through Fas/Fas ligand (Fas-L) interaction in the pathogenesis of rheumatoid arthritis (RA), we examined the expression of Fas antigen, Fas-L, and apoptosis in synovial tissue obtained from eight patients with RA and five patients with osteoarthritis (OA). Immunohistochemical staining demonstrated the significant expression of Fas antigen and Fas-L in RA synovial tissue compared with that in OA synovial tissue. Immunohistochemical staining and the DNA nick end labeling (TUNEL) method were combined and revealed that approximately 10 to 30% of Fas antigen-expressing cells in the RA synovium showed DNA fragmentation characteristic for apoptosis. In double-staining analysis, Fas-L was expressed on up to 10% of CD45RO-, CD4-, CD8-, or CD56-positive mononuclear cells in RA synovial tissue. Our results suggest that activated T cells and natural killer cells infiltrating into the RA synovium may contribute to the induction of apoptosis of RA synovial and mononuclear cells through Fas/Fas-L interaction.