Cellular interactions and control of collagenase secretion in the synovium.

Monocyte/macrophages release a factor, mononuclear cell factor (MCF), homologous with interleukin 1 (IL-1), which augments synthesis and release of collagenase and prostaglandins by connective tissue cells such as synovial cells and chondrocytes. The production of MCF is increased by interactions with immunoglobulins, collagens, and T lymphocytes. Human U937 cells, which behave as immature monocytes, do not produce MCF unless induced by a soluble product of activated T lymphocytes. Induction of MCF is augmented by 1,25-dihydroxyvitamin D. This cell culture system serves as a model for aspects of joint inflammation.