In Vitro Cultured Human Monocytes Release Fibroblast Proliferation Factor(s) Different From Interleukin 1

Human monocytes cultured in vitro released factors with growth stimulatory effect upon human dermal fibroblasts. Monocytes in RPMI 1640 released a growth enhancing activity in nearly constant amounts during in vitro differentiation to macrophage‐like cells. The growth stimulatory effect mediated by supernatants was reduced when lipopolysaccha‐ride (LPS) or opsonized zymosan particles (OpZ) were added to monocytes during the first 5 days of in vitro culture, thereafter reaching similar levels. The release of interleukin 1 (IL‐1) from monocytes was restricted to the first 2 days of culture. IL‐1 production by unstimulated monocytes was negligible, while LPS induced a high release of IL‐1 from monocytes. A rabbit antibody against human IL‐1 abolished the IL‐1 activity of the monocyte supernatants as assessed in a mouse thymocyte proliferation assay, but caused only a small reduction of the fibroblast proliferation activity. Thus, the fibroblast growth stimulatory activity mediated by monocytes was caused by factor(s) in addition to IL‐1.