Interleukin‐1β induces synthesis and secretion of interleukin‐6 in human chondrocytes

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Abstract
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.