Actinomycin D upregulates lipopolysaccharide induction of macrophage procoagulant expression and tumour necrosis factor‐alpha production
The antitumour antibiotic actinomycin D (Act D) and the aminosugar D‐galactosaminc both enhance the sensitivity of animals to bacterial lipopolysaccharide (LPS), Lipopolysaccharide stimulates macrophage membrane‐bound procoagulant activity (MPCA) and tumour necrosis factor‐alpha (TNF‐a) production in vitro. We investigated the cfTects of LPS combined with either Act D or tJ‐galactosaniine on procoagtilant and TNF‐x production in vitro. Actinomycin D directly induced procoagulant on the malignant monocytoid cell line WEHI 265. and synergized with LPS to enhance MPCA on both WEHI 265 cells and thioglycollate‐induccd peritoneal exudate maero‐phages. In the presence of Act D, exudate maerophages expressed procoagulant in response to concentrations of LPS lOOOOO‐fold lower than normally required. Pulsing experiments demon‐strated that LPS primed these cells within 4 h to respond to Act D. whereas 4 h priming with Aet D inhibited subsequent procoagulant induction by LPS. Although itseflects on TNF‐a production were less intense, low levels of Act D more than doubled TNF‐a produced by LPS‐stimulated exudate maerophages, Procoagulant expression and TNF‐a production were not always co‐ordinately expressed; interferon‐gamtna (IFN‐))synergi/ed with LPS to enhance both responses but when IFN‐) was combined with Act D only procoagulant was upregulated. t)‐galactosaminc failed to alTect these macrophage responses. Results indicate dillerent; vivo mechanisms of enhancement of LPS toxicity by these two agents.