Synovial fluid from patients with juvenile chronic arthritis (JCA) was found to stimulate the DNA synthesis of rat epiphyseal chondrocytes in serum-free primary cultures in vitro. The effect was dose-dependent and more pronounced than that observed with newborn calf serum. The cloning efficiency and colony size of chondrocytes in soft agar colony cultures were also stimulated. JCA synovial fluid also contained interleukin-1 (IL-1) activity when tested in a murine thymocyte proliferation assay. AcA 54 gel filtration chromatography showed similar elution pattern of the chondrocyte stimulating activity and the IL-1 activity, indicating that IL-1 might act as a chondrocyte growth factor in vitro. This assumption was further supported by experiments demonstrating a dose—related stimulation of chondrocyte DNA synthesis by natural guinea pig macrophage—derived IL—1 and recombinant human IL—1. As it has been shown that the articular cavity is vascularly connected with nearby epiphyseal plates, our results might give one explanation for the stimulation of bone growth often seen in the affected limb in children with monoarthritis.
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