Interleukin 2 inhibitor in synovial fluid

Since evidence for the presence of IL-2 activity in rheumatoid synovial fluid is conflicting, we have assayed IL-2 activity in synovial fluid from patients with rheumatoid arthritis (RA) and other articular diseases (OAD). Using the IL-2-dependent murine T cell line CTLL, IL-2 activity was not demonstrable in synovial fluid tested at concentrations ranging from 50% to 0.02%. There was an inhibitory effect on IL-2 activity in the bioassay of synovial fluid from 16 of the 22 patients with RA and 15 of the 16 with OAD. This inhibitory activity was heat-labile, precipitable by ammonium sulphate, reversible with excess IL-2 and was not significantly altered by preincubation of synovial fluid with CTLL. The mean inhibitory activity of synovial fluid from patients with RA was significantly reduced in comparison with that of synovial fluid from patients with OAD. Sera also had an inhibitory effect on IL-2 activity; however sera from patients with RA were less inhibitory than control sera but were more inhibitory than sera from patients with systemic lupus erythematosus. The deficiency in synovial fluid of an inhibitor of IL-2 activity may be relevant to the pathogenesis of RA.