Inhibitor of interleukin‐2 in rheumatoid synovial fluid

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Abstract
Although large numbers of T cells infiltrate the synovium of patients with rheumatoid arthritis (RA), the responses of these cells, as present in the blood and synovial fluid (SF), to exogenous interleukin‐2 (IL‐2) and their production of IL‐2 are diminished. To investigate this functional defect, RA SF were examined for the presence of inhibitors of IL‐1 and IL‐2. A factor was found which inhibited the IL‐2–induced proliferation of mitogen‐stimulated human T cells and the IL‐1–induced proliferation of C3H/Hej mouse thymocytes, but not IL‐1–induced fibroblast proliferation. On AcA 54 Ultrogel filtration, the inhibitory activity resided in a fraction with an apparent molecular weight of >70 kd and a major pI of 6.8. The inhibitory effect of RA SF on lymphocyte proliferation was partially corrected with IL‐2, but not with IL‐1. In the presence of RA SF, normal lymphocytes showed not only a decreased response to exogenous IL‐2, but also a decreased production of IL‐2. The presence of an inhibitor of IL‐2 in RA SF could contribute to the IL‐2–related T cell defects observed in RA.