Increased concentrations of interleukin-6 (IL-6) have been found in the synovial fluid of patients with osteoarthritis, rheumatoid arthritis and crystal-related joint deseases. It is therefore of great interest to identify the cells responsible for the production of IL-6, and to investigate whether IL-6 plays a role in the pathogenesisof degenerative or inflammatory joint diseases. Here we show that human interleukin-1β (IL-1β) induces IL-6 synthesis and secretion in differentiated human chondrocytes. In organ cultures resembling closely the in vivo system 106 chondrocytes incubated with 100 units of interleukin-1β per ml of medium led to the release of 6 × 103 units of IL-6 within 24 h. Chondrocytes cultured in agarose or as monolayers similary incubated with IL-1β produced even higher amounts of IL-6: 70 × 103 units per 106 cells within 24 h. The induction of IL-6 synthesis by IL-1β was also shown at the mRNA level. IL-6 secreted by stimulated chondrocytes showed heterogeneity upon Western blot analysis.
