Interleukin 2‐independent stimulation of rabbit chondrocyte collagenase and prostaglandin E2 production by an interleukin 1‐like factor

In the present study, interleukin 1 (IL 1)‐containing media from different sources, namely a murine macrophage cell line (P388D1), rabbit peritoneal macrophages, and human peripheral blood mononuclear cells, were compared for their effect on thymocyte proliferation and on collagenase and PGE2 secretion by chondrocytes. A high correlation was found between the enhancement of thymocyte proliferation and the induction of collagenase and PGE2 secretion by chondrocytes. Furthermore, a highly purified IL 1‐like factor, namely mononuclear cell factor (MCF) was also active on chondrocytes. The addition of highly purified IL 2 to rabbit chondrocytes had no effect on collagenase and PGE2 secretion induced by IL 1‐containing media. Our findings suggest that the factor which induced collagenase and PGE2 secretion by rabbit chondrocytes was an IL 1‐like factor. Thus, collagenase secretion by chondrocytes may be used as an IL 2‐insensitive assay for the detection of IL 1‐like factors.