title: Reversal of defective IL-6 production in lipopolysaccharide-tolerant mice by phorbol myristate acetate.
abstract: The development of LPS tolerance has been suggested to be mediated by an inhibition of cytokine synthesis. Here we have studied serum IL-6 and TNF levels in mice after LPS administration. Repeated administration of LPS (35 micrograms daily for 4 days) to mice induced a refractoriness (tolerance) to subsequent administrations of LPS in terms of induction of circulating IL-6 and TNF. To investigate the mechanism by which LPS down-regulates its own induction of cytokine synthesis and the relationship between IL-6 and TNF production, we attempted to revert the inhibition of IL-6 and TNF production using agents like PMA or IFN-gamma, previously reported to activate macrophage production of cytokines. Pretreatment with PMA (4 micrograms, 10 min before LPS) partially restored IL-6 production in LPS-tolerant mice given 2 micrograms LPS. On the other hand, PMA did not restore TNF induction in LPS-tolerant mice, even when administered with high doses of LPS (up to 200 micrograms). A similar reversal of LPS resistance to IL-6, but not TNF, induction by PMA was observed in genetically LPS-resistant C3H/HeJ mice. IFN-gamma also restored, although to a lesser extent than PMA, IL-6 production. However, unlike PMA, IFN-gamma could also partially restore TNF production in LPS-tolerant mice, although only when LPS was administered at high doses. By contrast with PMA, IFN-gamma was clearly more active in restoring TNF synthesis than that of IL-6. Similar results were obtained in genetically LPS-unresponsive C3H/HeJ mice. These data suggest that different mechanisms are implicated in the inhibition of IL-6 and TNF synthesis in LPS-tolerant mice and that part of this inhibition can be overcome by PMA or IFN-gamma.
authors.affiliation: Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Mengozzi
authors.forename: M
authors.initials: M
authors.lastname: Sironi
authors.forename: M
authors.initials: M
authors.lastname: Gadina
authors.forename: P
authors.initials: P
authors.lastname: Ghezzi
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D007108:Immune Tolerance / Q000187:drug effects; D007371:Interferon-gamma / Q000494:pharmacology; D015850:Interleukin-6 / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000502:physiology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
chemical_list: D015850:Interleukin-6; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D013755:Tetradecanoylphorbol Acetate