Impairment of growth of Listeria monocytogenes in THP-1 macrophages by granulocyte macrophage colony-stimulating factor: Release of tumor necrosis factor-α and nitric oxide

Abstract

Background. Listeria monocytogenes tends to survive in phagocytes. Granulocyte macrophage colony-stimulating factor (GM-CSF) protects mice against L. monocytogenes infection, and mice knocked out for the GM-CSF gene are more susceptible to these infections. Methods. THP-1 cells were used to characterize the GM-CSF receptor (binding isotherms; STAT5 phosphorylation), measure the intracellular growth of L. monocytogenes (5 h after phagocytosis), examine the influence of a 24-h incubation with GM-CSF before infection, measure the production of tumor necrosis factor (TNF)-α and the expression of nitric oxide synthase (iNOS), and evaluate the influence of anti-GM-CSF receptor (GM-CSFRα) and anti - TNF-α antibodies and the addition of N ω-nitro-L-arginine methyl ester (L-NAME) and catalase. Results. THP-1 cells display functional GM-CSFRα. GM-CSF impairs the intracellular growth of L. monocytogenes to ∼65% of its value in unstimulated cells. This effect is abolished by anti-GM-CSFRα, anti-TNF-α antibodies, and catalase (and, to a lesser extent, by L-NAME). GM-CSF stimulates the release of TNF-α and the expression of iNOS. TNF-α added to unstimulated cells (even in large amounts) does not fully reproduce the impairment in the growth of L. monocytogenes caused by GM-CSF. Conclusions. GM-CSF impairs the intracellular growth of L. monocytogenes by a synergistic action of the GM-CSF-triggered release of autocrine TNF-α and hydrogen peroxide and the production of NO (associated with the stimulation of the expression of iNOS).