Characterization of the release of human monocyte regulators of fibroblast proliferation

We have examined the mechanism of release of monocyte-derived mediators that stimulate fibroblast proliferation in vitro. Adherence of human monocytes promotes the rapid release of these factors and treatment of adherent peripheral blood mononuclear cell (APBM) cultures with lipopolysaccharide (LPS) greatly enhances the level of fibroblast-stimulating activity in the cell-free culture supernatant fluid (SN). Stimulation of phagocytosis or pinocytosis does not alter the release of these mediators from APBM cultures while trypan blue pretreatment of peripheral blood mononuclear cells (PBM) results in a significant reduction in fibroblast stimulation by PBM-SN. Protein synthesis was blocked by pretreatment of monocytes with puromycin and was accompanied by a concomitant reduction in the production of these mediators. Monocyte serine proteases appear to be essential for mediator synthesis or release since tosyl-lysine chloromethyl ketone (TLCK) and phenylmethyl sulfonyl fluoride (PMSF), irreversible inhibitors of serine esterase activity, diminish the release of fibroblast-stimulating factors. Furthermore, time course data indicate that monocytes rapidly release these products in vitro during the first 24 hr of culture with significantly reduced levels being produced from 24 to 96 hr. These data indicate that adherent human monocytes rapidly release fibroblast-activating mediators in vitro, requiring both protein synthesis and protease activity; furthermore LPS, but not phagocytosis, can enhance the release of these products.