Type I interferons are central mediators for antiviral responses. Using high-throughput functiona... more Type I interferons are central mediators for antiviral responses. Using high-throughput functional screening of interferon inducers, we have identified here a molecule we call interferon-b promoter stimulator 1 (IPS-1). Overexpression of IPS-1 induced type I interferon and interferon-inducible genes through activation of IRF3, IRF7 and NF-jB transcription factors. TBK1 and IKKi protein kinases were required for the IPS-1-mediated interferon induction. IPS-1 contained an N-terminal CARD-like structure that mediated interaction with the CARD of RIG-I and Mda5, which are cytoplasmic RNA helicases that sense viral infection. 'Knockdown' of IPS-1 by small interfering RNA blocked interferon induction by virus infection. Thus, IPS-1 is an adaptor involved in RIG-I-and Mda5-mediated antiviral immune responses.
Plasmacytoid dendritic cells (pDCs) recognize RNA virus infection via TLRs and consequently produ... more Plasmacytoid dendritic cells (pDCs) recognize RNA virus infection via TLRs and consequently produce vast amounts of type I IFN. Because nucleic acid-sensing TLRs reside in the intracellular membrane compartment, it is presumable that pDCs do not require cytoplasmic viral replication to recognize the infection. By checking Newcastle disease virus (NDV) RNA abundance in GFP+ and GFP− pDCs from Ifna6gfp mice, we found that NDV replication was not detected in IFN-producing pDCs. GFP+ pDC was induced in response to replication-incompetent NDV. In contrast, the replication-incompetent NDV failed to induce IFN-producing pDCs in type I IFNR-deficient mice. The lack of IFNR signaling led to the replication of NDV and the subsequent RIG-I-like helicase-dependent IFN-α production in pDCs. These results showed that detection of viruses via TLRs together with a type I IFN feedback system circumvents the requirement for viral replication-dependent recognition in pDCs.
The innate immune system recognizes influenza A virus via TLR 7 or retinoic acid-inducible gene I... more The innate immune system recognizes influenza A virus via TLR 7 or retinoic acid-inducible gene I in a cell-type specific manner in vitro, however, physiological function(s) of the MyD88- or interferon-β promoter stimulator 1 (IPS-1)-dependent signaling pathways in antiviral responses in vivo remain unclear. In this study, we show that although either MyD88- or IPS-1-signaling pathway was sufficient to control initial antiviral responses to intranasal influenza A virus infection, mice lacking both pathways failed to show antiviral responses, resulting in increased viral load in the lung. By contrast, induction of B cells or CD4 T cells specific to the dominant hemagglutinin or nuclear protein Ags respectively, was strictly dependent on MyD88 signaling, but not IPS-1 signaling, whereas induction of nuclear protein Ag-specific CD8 T cells was not impaired in the absence of either MyD88 or IPS-1. Moreover, vaccination of TLR7- and MyD88-deficient mice with inactivated virus failed to c...
Toll-like receptors (TLRs) recognize a variety of microbial components and mediate downstream sig... more Toll-like receptors (TLRs) recognize a variety of microbial components and mediate downstream signal transduction pathways that culminate in the activation of nuclear factor κB (NF-κB) and mitogen-activated protein (MAP) kinases. Trib1 is reportedly involved in the regulation of NF-κB and MAP kinases, as well as gene expression in vitro. To clarify the physiological function of Trib1 in TLR-mediated responses, we generated Trib1-deficient mice by gene targeting. Microarray analysis showed that Trib1-deficient macrophages exhibited a dysregulated expression pattern of lipopolysaccharide-inducible genes, whereas TLR-mediated activation of MAP kinases and NF-κB was normal. Trib1 was found to associate with NF-IL6 (also known as CCAAT/enhancer-binding protein β). NF-IL6–deficient cells showed opposite phenotypes to those in Trib1-deficient cells in terms of TLR-mediated responses. Moreover, overexpression of Trib1 inhibited NF-IL6–dependent gene expression by down-regulating NF-IL6 prot...
Type I interferons (IFNs) are critical for antiviral responses. Here we generated a knockin mouse... more Type I interferons (IFNs) are critical for antiviral responses. Here we generated a knockin mouse in which green fluorescence protein (GFP) was expressed under the control of the Ifna6 promoter. Virus-induced expression of GFP recapitulated various IFN-a subtypes. Systemic infection of the mice with Newcastle disease virus (NDV) increased GFP + plasmacytoid dendritic cells (pDCs) via the Toll-like receptor system, and GFP + conventional dendritic cells (cDCs) and macrophages via the RIG-I-like helicase system. By contrast, lung infection with NDV led to IFN-a production in alveolar macrophages (AMs) and cDCs, but not in pDCs. Specific depletion of AMs caused a marked defect in the initial viral elimination in the lung. pDCs produced IFN-a in the absence of AM-mediated viral recognition, suggesting that pDCs function when the first defense line is broken. Thus, AMs act as a type I IFN producer that is important for the initial responses to viral infection in the lung.
Secondary bacterial infection is a common sequela to viral infection and is associated with incre... more Secondary bacterial infection is a common sequela to viral infection and is associated with increased lethality and morbidity. However, the underlying mechanisms remain poorly understood. We show that the TLR3/MDA5 agonist poly I:C or viral infection dramatically augments signaling via the NLRs Nod1 and Nod2 and enhances the production of proinflammatory cytokines. Enhanced Nod1 and Nod2 signaling by poly I:C required the TLR3/MDA5 adaptors TRIF and IPS-1 and was mediated by type I IFNs. Mechanistically, poly I:C or IFN-b induced the expression of Nod1, Nod2, and the Nod-signaling adaptor Rip2. Systemic administration of poly I:C or IFN-b or infection with murine norovirus-1 promoted inflammation and lethality in mice superinfected with E. coli, which was independent of bacterial burden but attenuated in the absence of Nod1/Nod2 or Rip2. Thus, crosstalk between type I IFNs and Nod1/Nod2 signaling promotes bacterial recognition, but induces harmful effects in the virally infected host. Cell Host & Microbe Crosstalk between Nod1/Nod2 and Type I IFNs
Biochemical and Biophysical Research Communications, 2009
Toll-like receptors (TLRs) are the best-characterized membrane-bound receptors in innate immune c... more Toll-like receptors (TLRs) are the best-characterized membrane-bound receptors in innate immune cells, including macrophages and dendritic cells. Upon recognition of specific ligands originating from pathogen-and modified selfderived molecules, TLRs trigger intracellular signaling cascades that involve various adaptor proteins and enzymes, resulting in the generation of proinflammatory and antimicrobial responses through the activation of transcription factors such as nuclear factor-κB. TLR-dependent signaling pathways are tightly regulated during innate immune responses by a variety of negative regulators. This review focuses on the newly described regulation of TLR-dependent signaling pathways, and emphasizes the roles of TLRs in innate immunity. Efforts to modulate these regulatory pathways and signaling molecules may result in the development of new therapeutic strategies through TLR-based therapy.
Type I interferons are central mediators for antiviral responses. Using high-throughput functiona... more Type I interferons are central mediators for antiviral responses. Using high-throughput functional screening of interferon inducers, we have identified here a molecule we call interferon-b promoter stimulator 1 (IPS-1). Overexpression of IPS-1 induced type I interferon and interferon-inducible genes through activation of IRF3, IRF7 and NF-jB transcription factors. TBK1 and IKKi protein kinases were required for the IPS-1-mediated interferon induction. IPS-1 contained an N-terminal CARD-like structure that mediated interaction with the CARD of RIG-I and Mda5, which are cytoplasmic RNA helicases that sense viral infection. 'Knockdown' of IPS-1 by small interfering RNA blocked interferon induction by virus infection. Thus, IPS-1 is an adaptor involved in RIG-I-and Mda5-mediated antiviral immune responses.
Plasmacytoid dendritic cells (pDCs) recognize RNA virus infection via TLRs and consequently produ... more Plasmacytoid dendritic cells (pDCs) recognize RNA virus infection via TLRs and consequently produce vast amounts of type I IFN. Because nucleic acid-sensing TLRs reside in the intracellular membrane compartment, it is presumable that pDCs do not require cytoplasmic viral replication to recognize the infection. By checking Newcastle disease virus (NDV) RNA abundance in GFP+ and GFP− pDCs from Ifna6gfp mice, we found that NDV replication was not detected in IFN-producing pDCs. GFP+ pDC was induced in response to replication-incompetent NDV. In contrast, the replication-incompetent NDV failed to induce IFN-producing pDCs in type I IFNR-deficient mice. The lack of IFNR signaling led to the replication of NDV and the subsequent RIG-I-like helicase-dependent IFN-α production in pDCs. These results showed that detection of viruses via TLRs together with a type I IFN feedback system circumvents the requirement for viral replication-dependent recognition in pDCs.
The innate immune system recognizes influenza A virus via TLR 7 or retinoic acid-inducible gene I... more The innate immune system recognizes influenza A virus via TLR 7 or retinoic acid-inducible gene I in a cell-type specific manner in vitro, however, physiological function(s) of the MyD88- or interferon-β promoter stimulator 1 (IPS-1)-dependent signaling pathways in antiviral responses in vivo remain unclear. In this study, we show that although either MyD88- or IPS-1-signaling pathway was sufficient to control initial antiviral responses to intranasal influenza A virus infection, mice lacking both pathways failed to show antiviral responses, resulting in increased viral load in the lung. By contrast, induction of B cells or CD4 T cells specific to the dominant hemagglutinin or nuclear protein Ags respectively, was strictly dependent on MyD88 signaling, but not IPS-1 signaling, whereas induction of nuclear protein Ag-specific CD8 T cells was not impaired in the absence of either MyD88 or IPS-1. Moreover, vaccination of TLR7- and MyD88-deficient mice with inactivated virus failed to c...
Toll-like receptors (TLRs) recognize a variety of microbial components and mediate downstream sig... more Toll-like receptors (TLRs) recognize a variety of microbial components and mediate downstream signal transduction pathways that culminate in the activation of nuclear factor κB (NF-κB) and mitogen-activated protein (MAP) kinases. Trib1 is reportedly involved in the regulation of NF-κB and MAP kinases, as well as gene expression in vitro. To clarify the physiological function of Trib1 in TLR-mediated responses, we generated Trib1-deficient mice by gene targeting. Microarray analysis showed that Trib1-deficient macrophages exhibited a dysregulated expression pattern of lipopolysaccharide-inducible genes, whereas TLR-mediated activation of MAP kinases and NF-κB was normal. Trib1 was found to associate with NF-IL6 (also known as CCAAT/enhancer-binding protein β). NF-IL6–deficient cells showed opposite phenotypes to those in Trib1-deficient cells in terms of TLR-mediated responses. Moreover, overexpression of Trib1 inhibited NF-IL6–dependent gene expression by down-regulating NF-IL6 prot...
Type I interferons (IFNs) are critical for antiviral responses. Here we generated a knockin mouse... more Type I interferons (IFNs) are critical for antiviral responses. Here we generated a knockin mouse in which green fluorescence protein (GFP) was expressed under the control of the Ifna6 promoter. Virus-induced expression of GFP recapitulated various IFN-a subtypes. Systemic infection of the mice with Newcastle disease virus (NDV) increased GFP + plasmacytoid dendritic cells (pDCs) via the Toll-like receptor system, and GFP + conventional dendritic cells (cDCs) and macrophages via the RIG-I-like helicase system. By contrast, lung infection with NDV led to IFN-a production in alveolar macrophages (AMs) and cDCs, but not in pDCs. Specific depletion of AMs caused a marked defect in the initial viral elimination in the lung. pDCs produced IFN-a in the absence of AM-mediated viral recognition, suggesting that pDCs function when the first defense line is broken. Thus, AMs act as a type I IFN producer that is important for the initial responses to viral infection in the lung.
Secondary bacterial infection is a common sequela to viral infection and is associated with incre... more Secondary bacterial infection is a common sequela to viral infection and is associated with increased lethality and morbidity. However, the underlying mechanisms remain poorly understood. We show that the TLR3/MDA5 agonist poly I:C or viral infection dramatically augments signaling via the NLRs Nod1 and Nod2 and enhances the production of proinflammatory cytokines. Enhanced Nod1 and Nod2 signaling by poly I:C required the TLR3/MDA5 adaptors TRIF and IPS-1 and was mediated by type I IFNs. Mechanistically, poly I:C or IFN-b induced the expression of Nod1, Nod2, and the Nod-signaling adaptor Rip2. Systemic administration of poly I:C or IFN-b or infection with murine norovirus-1 promoted inflammation and lethality in mice superinfected with E. coli, which was independent of bacterial burden but attenuated in the absence of Nod1/Nod2 or Rip2. Thus, crosstalk between type I IFNs and Nod1/Nod2 signaling promotes bacterial recognition, but induces harmful effects in the virally infected host. Cell Host & Microbe Crosstalk between Nod1/Nod2 and Type I IFNs
Biochemical and Biophysical Research Communications, 2009
Toll-like receptors (TLRs) are the best-characterized membrane-bound receptors in innate immune c... more Toll-like receptors (TLRs) are the best-characterized membrane-bound receptors in innate immune cells, including macrophages and dendritic cells. Upon recognition of specific ligands originating from pathogen-and modified selfderived molecules, TLRs trigger intracellular signaling cascades that involve various adaptor proteins and enzymes, resulting in the generation of proinflammatory and antimicrobial responses through the activation of transcription factors such as nuclear factor-κB. TLR-dependent signaling pathways are tightly regulated during innate immune responses by a variety of negative regulators. This review focuses on the newly described regulation of TLR-dependent signaling pathways, and emphasizes the roles of TLRs in innate immunity. Efforts to modulate these regulatory pathways and signaling molecules may result in the development of new therapeutic strategies through TLR-based therapy.
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Papers by Himanshu Kumar