Cytokine production by synovial T cells in rheumatoid arthritis

OBJECTIVE: To investigate the production of cytokines by T cells in patients with rheumatoid arthritis (RA), reactive arthritis (REA) and osteoarthritis (OA). METHODS: The lymphokines interleukin (IL)-2, IL-4, interferon gamma (IFN-gamma) and tumour necrosis factor beta (TNF-beta), as well as the monokines IL-1, IL-6 and TNF-alpha, were measured by immunoassays in sera and synovial fluid (SF) from patients with RA, REA and OA. In addition, cytokine expression was studied by immunohistochemistry in synovial membrane tissue sections from patients with RA and OA. RESULTS: Almost 60% of RA sera contained at least one of the cytokines investigated, though in low concentrations, whereas cytokines were generally not detectable in sera from REA and OA patients. In contrast, cytokines were found in virtually all SF; thus, the majority of SF from RA patients contained IFN-gamma (median level 17 pg/ml) in addition to the monokines IL-6 (4700 pg/ml) and TNF-alpha (157 pg/ml). IFN-gamma and IL-6 (but not TNF-alpha) were also frequently measured in SF from REA patients, whereas OA samples typically contained only IL-6. Immunohistochemical analysis of tissue sections from RA patients revealed lymphokine expression in 0.1-0.3% of T cells, particularly IL-2 and IFN-gamma, and to a lesser extent also IL-4. Interestingly, the expression of TNF-alpha and IL-6 by synovial T cells was also observed. The majority of cytokine-expressing T cells were CD4-positive T-helper cells typically found in perivascular areas, whereas cytokine-producing CD8-positive T cells were found distributed throughout the synovium. As expected, in specimens from OA patients, T cells were much less abundant and expression of cytokines could not be detected. CONCLUSION: These data clearly demonstrate production of cytokines by T cells in RA synovial tissue, indicating that activated T cells play a role in the pathophysiological events of RA.