Correlation of synovial fluid interleukin 6 (IL-6) activities with IgG concentrations in patients with inflammatory joint disease and osteoarthritis.

Synovial fluids of patients with rheumatoid arthritis, osteoarthritis, psoriatic arthritis, reactive arthritis and Reiter's syndrome were examined for their concentrations of interleukin 6 (IL-6) in a proliferation assay with the IL-6 dependent hybridoma cell line B13.29 (subclone B9). IL-6 activity was significantly higher in the synovial fluids of patients with rheumatoid arthritis and psoriatic arthritis than in patients with osteoarthritis. Significant correlations were shown between the concentrations of synovial fluid IL-6 and IgG. These findings may contribute to the understanding of the enhanced immunoglobulin production by synovial mononuclear cells in patients with inflammatory joint disease.