Activated protein C inhibits tumor necrosis factor and macrophage migration inhibitory factor production in monocytes

The precise regulatory mechanisms of amplification and downregulation of th e pro- and antiinflammatory cytokines in the inflammatory response have not been fully delineated. Although activated protein C (APC) and its precurso r protein C (PC) have recently been reported to be promising therapeutic ag ents in the management of meningococcal sepsis, direct evidence for the ant i-inflammatory effect remains scarce. We report that APC inhibits in vitro the release of tumor necrosis factor (TNF) and macrophage migration inhibit ory factor (MIF), two known cytokine mediators of bacterial septic shock, f rom lipopolysaccharide (LPS)-stimulated human monocytes, The THP-1 monocyti c cell line, when stimulated with LPS and concomitant APC, exhibited a mark ed reduction in the release of TNF and MIF protein in a concentration-depen dent manner compared to cells stimulated with LPS alone. This effect was ob served only when incubations were performed in serum-free media, but not in the presence of 1-10% serum. Serum-mediated inhibition could only be overc ome by increasing APC concentrations to far beyond physiological levels, su ggesting the presence of endogenous serum-derived APC inhibitors. Inhibitio n of MIF release by APC was found to be independent of TNF, as stimulation of MIF release by LPS was unaltered in the presence of anti-TNF antibodies. Our data confirm that the suggested anti-inflammatory properties of APC ar e due to direct inhibition of the release of the pro-inflammatory monokine TNF, and imply that the anti-inflammatory action of APC is also mediated vi a inhibition of MIF release.