title: Suppression of interleukin-12 production by human monocytes after preincubation with lipopolysaccharide.
abstract: Interleukin-12 (IL-12) is a potent proinflammatory and immunoregulatory cytokine skewing T lymphocytes to express a type 1 cytokine pattern. Optimal expression of IL-12 mRNA and bioactivity in vitro requires specific priming of monocytes by interferon-gamma (IFN-gamma) or granulocyte-macrophage colony-stimulating factor (GM-CSF) before lipopolysaccharide (LPS) stimulation. We show here for the first time that the production of IL-12 by IFN-gamma- or GM-CSF-primed human monocytes can be completely suppressed by preincubation with LPS (from Escherichia coli Serotype 055:B5) for 6 to 24 hours before the priming procedure. A dose-dependent suppression of IL-12p70 was measured on the levels of intracellular cytokine production and cytokine secretion. mRNA studies on the expression of p40 and p35 showed an LPS-induced downregulation of both subunits. The results of several different experimental approaches suggest that IL-12 downregulation was not due to endogenous IL-10, IL-4, prostaglandin E(2) (PGE(2)), tumor necrosis factor-alpha (TNF-alpha), or nitric oxide (NO) production induced by LPS. Moreover, preincubation of monocytes with LPS did not lead to a downregulation of the CD14 antigen, which is an LPS receptor. LPS preincubation in this experimental setting did not result in a general hyporesponsiveness of the monocytes, as IL-6 production as well as IFN-gamma-induced upregulation of CD54 did not decline. Downregulation of IL-12 was not due to changes in mRNA stability. These findings show that the immunoregulatory important cytokine, IL-12, underlies itself a complex regulation.
authors.affiliation: Hannover Medical University, Department of Dermatology and Allergology, Hannover, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Wittmann
authors.forename: V A
authors.initials: VA
authors.lastname: Larsson
authors.forename: P
authors.initials: P
authors.lastname: Schmidt
authors.forename: G
authors.initials: G
authors.lastname: Begemann
authors.forename: A
authors.initials: A
authors.lastname: Kapp
authors.forename: T
authors.initials: T
authors.lastname: Werfel
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects; D005434:Flow Cytometry; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D018664:Interleukin-12 / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D009000:Monocytes / Q000276:immunology / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: D000998:Antiviral Agents; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D018664:Interleukin-12; D007371:Interferon-gamma; D016178:Granulocyte-Macrophage Colony-Stimulating Factor