Interleukin-6 in synovial fluid from patients with arthritis.

Synovial fluid and serum from patients with rheumatoid arthritis, other inflammatory arthritides, and traumatic arthritis were assayed for the presence of interleukin-6 (IL-6) by means of an IL-6-dependent mouse hybridoma cell line. The cytokine was detected in all the samples of synovial fluid (range 50-22000 U/ml). IL-6 in synovial fluid was positively correlated (r = 0.58, P = 0.03) with the erythrocyte sedimentation rate in patients with inflammatory arthritis. In serum, the concentration of IL-6 was slightly elevated in some patients with rheumatoid arthritis. The results demonstrate that IL-6 is released into synovial fluid in joints affected by arthritis, and there appears to be an association between the levels of IL-6 and disease activity.