ABSTRACT
Like viruses, intracellular bacteria stimulate their host cells to produce type I IFNs (IFN-alpha and IFN-beta). In our study, we investigated the signals and molecules relevant for the synthesis of and response to IFN by mouse macrophages infected with Listeria monocytogenes. We report that IFN-beta is the critical immediate-early IFN made during infection, because the synthesis of all other type I IFN, expression of a subset of infection-induced genes, and the biological response to type I IFN was lost upon IFN-beta deficiency. The induction of IFN-beta mRNA and the IFN-beta-dependent sensitization of macrophages to bacteria-induced death, in turn, was absolutely dependent upon the presence of the transcription factor IFN regulatory factor 3 (IRF3). IFN-beta synthesis and signal transduction occurred in macrophages deficient for TLR or their adaptors MyD88, TRIF, or TRAM. Expression of Nod2, a candidate receptor for intracellular bacteria, increased during infection, but the protein was not required for Listeria-induced signal transduction to the Ifn-beta gene. Based on our data, we propose that IRF3 is a convergence point for signals derived from structurally unrelated intracellular pathogens, and that L. monocytogenes stimulates a novel TLR- and Nod2-independent pathway to target IRF3 and the type I IFN genes.
Subject(s)
DNA-Binding Proteins/physiology , Gene Expression Regulation/immunology , Interferon-beta/biosynthesis , Intracellular Fluid/immunology , Intracellular Fluid/microbiology , Intracellular Signaling Peptides and Proteins/physiology , Membrane Glycoproteins/physiology , Receptors, Cell Surface/physiology , Transcription Factors/physiology , Adaptor Proteins, Signal Transducing , Adaptor Proteins, Vesicular Transport/deficiency , Animals , Antigens, Differentiation , Cells, Cultured , DNA-Binding Proteins/deficiency , DNA-Binding Proteins/genetics , Humans , Interferon Regulatory Factor-3 , Interferon-alpha/biosynthesis , Interferon-alpha/physiology , Interferon-beta/deficiency , Interferon-beta/genetics , Interferon-beta/physiology , Intracellular Fluid/metabolism , Intracellular Signaling Peptides and Proteins/deficiency , Intracellular Signaling Peptides and Proteins/genetics , Listeria monocytogenes/immunology , Macrophages/immunology , Macrophages/metabolism , Macrophages/microbiology , Membrane Glycoproteins/deficiency , Membrane Glycoproteins/genetics , Membrane Proteins/deficiency , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Mice, Knockout , Myeloid Differentiation Factor 88 , Nod2 Signaling Adaptor Protein , Protein Isoforms/biosynthesis , Protein Isoforms/physiology , Receptors, Cell Surface/deficiency , Receptors, Cell Surface/genetics , Receptors, Immunologic/deficiency , Signal Transduction/genetics , Signal Transduction/immunology , Toll-Like Receptors , Transcription Factors/deficiency , Transcription Factors/geneticsABSTRACT
Type I IFNs (IFN-alpha/beta) modulate innate immune responses. Here we show activation of transcription factor IFN regulatory factor 3, the synthesis of large amounts of IFN-beta mRNA, and type I IFN signal transduction in macrophages infected with Listeria monocytogenes. Expression of the bacterial virulence protein listeriolysin O was necessary, but not sufficient, for efficient IFN-beta production. Signaling through a pathway involving the type I IFN receptor and Stat1 sensitized macrophages to L. monocytogenes-induced cell death in a manner not requiring inducible NO synthase (nitric oxide synthase 2) or protein kinase R, potential effectors of type I IFN action during microbial infections. The data stress the importance of type I IFN for the course of infections with intracellular bacteria and suggest that factors other than listeriolysin O contribute to macrophage death during Listeria infection.
