In vitro activation of human chondrocytes and synoviocytes by a human interleukin‐1‐like factor

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Abstract
Monocytes have been shown to secrete factors which stimulate the destruction of cartilage. Since one of the monocyte products, interleukin-1 (IL-1), has been shown to stimulate the release of collagenase and prostaglandin E from synoviocytes, we have investigated whether IL-1 is also responsible for chondrocyte activation. Purified preparations of IL-1 derived from human blood monocytes stimulated the production of prostaglandin E and plasminogen activator by human articular chondrocytes. After Sephadex G-75 chromatography, the lymphocyte-activating and the chondrocyteactivating activities of IL-1 eluted together in the regions corresponding to the void volume and to Kav = 0.2—0.3 (Mr 30,000—45,000) and Kav = 0.5—0.65 (Mr 12,000—17,000). The major peak of stimulating activity was the 12,000—17,000 dalton peak. Upon further analysis of the 12,000—17,000 dalton peak by isoelectric focusing, the major peak of lymphocyte-activating factor activity was recovered at a pI of 6.3 with a minor peak at 4.6—5.3. Similar patterns of activity were observed when the fractions were assayed for the stimulation of the production of prostaglandin E and plasminogen activator by human chondrocytes and of prostaglandin E by human synoviocytes. Treatment of the partially purified lymphocyte activating factor with phenylglyoxal reduced the thymocyte-stimulating activity 99% and the chondrocyte-stimulating activity 100%. These results suggest that IL-1 may stimulate the degradation of connective tissues during inflammation.