Objective: To test synovial fluid (SF) for the presence of soluble fragments originating from distinct tumor necrosis factor receptors (TNF-sR55 and TNF-sR75) which bind to TNF and inhibit its biologic activity.
Methods: TNF-sR55 and TNF-sR75 were measured in 62 SF samples by specific immunoassays using monoclonal antibodies.
Results: Both TNF-sR were present in all of the SF tested. Their concentrations were higher in SF from patients with seropositive rheumatoid arthritis than in patients with other inflammatory arthritides. The relative amount of TNF-sR75, as compared with TNF-sR55, was higher in seropositive RA SF than in other SF.
Conclusion: The balance between TNF and its specific inhibitors may be critical to the biologic outcome mediated by this cytokine.