title: Inhibition of lipopolysaccharide-induced signal transduction in endotoxin-tolerized mouse macrophages: dysregulation of cytokine, chemokine, and toll-like receptor 2 and 4 gene expression.
abstract: In this study, the effect of in vitro endotoxin tolerance on LPS-induced mitogen-activated protein kinase activation, transcription factor induction, and cytokine, chemokine, and Toll-like receptor (TLR) 2 and 4 gene expression, as well as the involvement of TNF and IL-1 signaling pathways in tolerance, were examined. Pretreatment of mouse macrophages with LPS inhibited phosphorylation of the extracellular signal-regulated kinases, c-Jun NH2-terminal kinases, and p38 kinase; degradation of I-kappaBalpha (inhibitory protein that dissociates from NF-kappaB) and I-kappaBbeta; and activation of the transcription factors NF-kappaB and AP-1 in response to subsequent LPS stimulation. These changes were accompanied by suppression of LPS-induced expression of mRNA for GM-CSF, IFN-gamma-inducible protein-10, KC, JE/monocyte chemoattractant protein-1, macrophage-inflammatory protein-1beta, and macrophage-inflammatory protein-2, with concurrent inhibition of chemokine secretion. In contrast to control cells, endotoxin-tolerant macrophages exhibited an increased basal level of TLR2 mRNA, and failed to increase levels of TLR2 mRNA or to down-regulate TLR4 gene expression upon restimulation with LPS. As judged by transcription factor activation, LPS and IL-1 were found to induce a state of cross-tolerance against each other, while no such reciprocal effect was seen for LPS and TNF-alpha. In addition, macrophages from TNFR I/II double knockout mice were LPS tolerizable, and blocking of endogenous TNF-alpha with TNFR-Fc fusion protein did not affect the capacity of LPS to tolerize macrophages. These data extend our understanding of LPS-signaling mechanisms that are inhibited in endotoxin-tolerized macrophages and suggest that endotoxin tolerance might result from impaired expression and/or functions of common signaling intermediates involved in LPS and IL-1 signaling.
authors.affiliation: Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: Medvedev
authors.forename: K M
authors.initials: KM
authors.lastname: Kopydlowski
authors.forename: S N
authors.initials: SN
authors.lastname: Vogel
mesh_terms: D000818:Animals; D018925:Chemokines / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D016207:Cytokines / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D015536:Down-Regulation / Q000235:genetics / Q000276:immunology; D029721:Drosophila Proteins; D005786:Gene Expression Regulation / Q000276:immunology*; D007108:Immune Tolerance / Q000235:genetics*; D007375:Interleukin-1 / Q000502:physiology; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors / Q000276:immunology*; D020935:MAP Kinase Signaling System / Q000276:immunology; D017737:Macrophages, Peritoneal / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism; D012333:RNA, Messenger / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology
chemical_list: D018925:Chemokines; D016207:Cytokines; D029721:Drosophila Proteins; D007375:Interleukin-1; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D018808:Transcription Factor AP-1; D014409:Tumor Necrosis Factor-alpha