title: Type I IFN induction in response to Listeria monocytogenes in human macrophages: evidence for a differential activation of IFN regulatory factor 3 (IRF3).
abstract: Listeria monocytogenes is a prototypic bacterium for studying innate and adaptive cellular immunity as well as host defense. Using human monocyte-derived macrophages, we report that an infection with a wild-type strain, but not a listeriolysin O-deficient strain, of the Gram-positive bacterium L. monocytogenes induces expression of IFN-beta and a bioactive type I IFN response. Investigating the activation of signaling pathways in human macrophages after infection revealed that a wild-type strain and a hemolysin-deficient strain of L. monocytogenes activated the NF-kappaB pathway and induced a comparable TNF response. p38 MAPK and activating transcription factor 2 were phosphorylated following infection with either strain, and IFN-beta gene expression induced by wild-type L. monocytogenes was reduced when p38 was inhibited. However, neither IFN regulatory factor (IRF) 3 translocation to the nucleus nor posttranslational modifications and dimerizations were observed after L. monocytogenes infection. In contrast, vesicular stomatitis virus and LPS triggered IRF3 activation and signaling. When IRF3 was knocked down using small interfering RNA, a L. monocytogenes-induced IFN-beta response remained unaffected whereas a vesicular stomatitis virus-triggered response was reduced. Evidence against the possibility that IRF7 acts in place of IRF3 is provided. Thus, we show that wild-type L. monocytogenes induced an IFN-beta response in human macrophages and propose that this response involves p38 MAPK and activating transcription factor 2. Using various stimuli, we show that IRF3 is differentially activated during type I IFN responses in human macrophages.
authors.affiliation: Institute of Veterinary Virology, University of Bern, Bern, Switzerland. reimer@ivv.unibe.ch
authors.forename: Thornik
authors.initials: T
authors.lastname: Reimer
authors.forename: Matthias
authors.initials: M
authors.lastname: Schweizer
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Jungi
mesh_terms: D051698:Activating Transcription Factor 2 / Q000276:immunology / Q000378:metabolism; D001427:Bacterial Toxins; D015153:Blotting, Western; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D024202:Electrophoretic Mobility Shift Assay; D004797:Enzyme-Linked Immunosorbent Assay; D005455:Fluorescent Antibody Technique; D006360:Heat-Shock Proteins / Q000172:deficiency; D006460:Hemolysin Proteins / Q000172:deficiency; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000276:immunology* / Q000378:metabolism; D007370:Interferon Type I / Q000276:immunology* / Q000378:metabolism; D016899:Interferon-beta / Q000276:immunology / Q000378:metabolism; D008089:Listeria monocytogenes / Q000276:immunology; D008088:Listeriosis / Q000276:immunology*; D008262:Macrophage Activation / Q000276:immunology*; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D016328:NF-kappa B / Q000276:immunology / Q000378:metabolism; D010588:Phagosomes / Q000378:metabolism; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000276:immunology / Q000378:metabolism
chemical_list: D051698:Activating Transcription Factor 2; D001427:Bacterial Toxins; D006360:Heat-Shock Proteins; D006460:Hemolysin Proteins; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; D007370:Interferon Type I; D016328:NF-kappa B; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; D016899:Interferon-beta; D048051:p38 Mitogen-Activated Protein Kinases; C038705:hlyA protein, Listeria monocytogenes