Influenza A Virus Lacking the NS1 Gene Replicates in Interferon-Deficient Systems

Garcı́a-Sastre, Adolfo; Egorov, Andrej; Matassov, Demetrius; Brandt, Sabine; Levy, David E.; Durbin, Joan E.; Palese, Peter; Muster, Thomas

doi:10.1006/viro.1998.9508

Cited by 917 publications

(877 citation statements)

References 32 publications

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“…We next considered the possibility that hvPR8 might carry mutations that lead to particularly strong suppression of the antiviral IFN response in infected cells. Enhanced virulence of human and avian FLUAV strains has been attributed to the NS1 gene that is known to suppress IFN synthesis in virus-infected cells (5,16,18,19). We found that both hvPR8 and standard lvPR8 suppressed early IFN synthesis in lungs of infected mice very strongly, indicating that the NS1 proteins of both viruses act as functional IFN antagonists.…”

Section: Discussionmentioning

confidence: 71%

“…Because it was possible that the high virulence of hvPR8 in Mx1 ϩ/ϩ mice resulted from extraordinary suppression of virus-induced IFN synthesis, we determined the capacity of hvPR8 and lvPR8 to induce IFN-␤ in cell culture and lungs of infected mice. As positive control for these experiments, we used PR8delNS1, a NS1-deficient PR8 mutant virus which is a potent IFN inducer (16). To avoid complications resulting from differences in virus growth kinetics, the mice were infected with a high dose of virus (10 5 pfu) and killed 10 h later.…”

Section: Ifn Protects Against Hvpr8 In Mx1mentioning

confidence: 99%

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Replication fitness determines high virulence of influenza A virus in mice carrying functional Mx1 resistance gene

Grimm

Staeheli

Hufbauer

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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176

177

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The IFN-induced resistance factor Mx1 is a critical component of innate immunity against influenza A viruses (FLUAV) in mice. Animals carrying a wild-type Mx1 gene (Mx1 ؉/؉ ) differ from regular laboratory mice (Mx1 ؊/؊ ) in that they are highly resistant to infection with standard FLUAV strains. We identified an extraordinary variant of the FLUAV strain, A/PR/8/34 (H1N1) (designated hvPR8), which is unusually virulent in Mx1 ؉/؉ mice. hvPR8 was well controlled in Mx1 ؉/؉ but not Mx1 ؊/؊ mice provided that the animals were treated with IFN before infection, indicating that hvPR8 exhibits normal sensitivity to growth restriction by Mx1. hvPR8 multiplied much faster than standard PR8 early in infection because of highly efficient viral gene expression in infected cells. Studies with reassortant viruses containing defined genome segments of both hvPR8 and standard PR8 demonstrated that the HA, neuraminidase, and polymerase genes of hvPR8 all contributed to virulence, indicating that efficient host cell entry and early gene expression renders hvPR8 highly pathogenic. These results reveal a surprisingly simple concept of how influenza viruses may gain virulence and illustrate that high speed of virus growth can outcompete the antiviral response of the infected host.influenza virus reassortants ͉ interferon ͉ Mx GTPase ͉ innate immunity ͉ antiviral

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Section: Discussionmentioning

confidence: 71%

Section: Ifn Protects Against Hvpr8 In Mx1mentioning

confidence: 99%

Replication fitness determines high virulence of influenza A virus in mice carrying functional Mx1 resistance gene

Grimm

Staeheli

Hufbauer

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

176

177

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“…NS1 encoded by inf luenza A virus was among those first selected because it is encoded by an overlapping gene and inf luences virulence and virus accumulation but is not essential for viral replication (33), which are common features of many known viral silencing suppressors such as the nodaviral B2 and plant viral 2b proteins (12,16,34). We found that NS1 protein expressed from a cotransfected plasmid indeed rescued GFP expression from pFR1gfp in Drosophila cells (Fig.…”

Section: Identification Of Mammalian Viral Proteins That Suppress Thementioning

confidence: 72%

Interferon antagonist proteins of influenza and vaccinia viruses are suppressors of RNA silencing

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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371

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Homology-dependent RNA silencing occurs in many eukaryotic cells. We reported recently that nodaviral infection triggers an RNA silencing-based antiviral response (RSAR) in Drosophila, which is capable of a rapid virus clearance in the absence of expression of a virus-encoded suppressor. Here, we present further evidence to show that the Drosophila RSAR is mediated by the RNA interference (RNAi) pathway, as the viral suppressor of RSAR inhibits experimental RNAi initiated by exogenous double-stranded RNA and RSAR requires the RNAi machinery. We demonstrate that RNAi also functions as a natural antiviral immunity in mosquito cells. We further show that vaccinia virus and human influenza A, B, and C viruses each encode an essential protein that suppresses RSAR in Drosophila. The vaccinia and influenza viral suppressors, E3L and NS1, are distinct double-stranded RNA-binding proteins and essential for pathogenesis by inhibiting the mammalian IFN-regulated innate antiviral response. We found that the double-stranded RNA-binding domain of NS1, implicated in innate immunity suppression, is both essential and sufficient for RSAR suppression. These findings provide evidence that mammalian virus proteins can inhibit RNA silencing, implicating this mechanism as a nucleic acid-based antiviral immunity in mammalian cells. R NA silencing is a unique RNA-guided gene regulatory mechanism that operates in a wide range of eukaryotic organisms from plants to mammals (1). A feature common to all RNA silencing processes is the production of 21-to 26-nt small RNAs from structured or double-stranded RNA (dsRNA) by the endoribonuclease Dicer (2-6). These small interfering RNAs (siRNAs) control the specificity of RNA silencing in a homology-dependent manner by means of an RNA-induced silencing complex (RISC), of which Argonaute-2 (AGO2) is an essential protein component (1,7,8). RNA silencing in fungi, plants, and worms involves a cellular RNA-dependent RNA polymerase (RdRP); however, the multiple-turnover RISC may mediate RNA silencing in absence of a cellular RdRP in Drosophila and mammalian cells (1, 9-11).We reported recently that infection of cultured Drosophila cells with the plus-strand RNA Nodavirus flock house virus (FHV), triggers specific silencing of FHV RNAs that is associated with accumulation of 22-nt siRNAs (12). Silencing of the replicating viral RNAs is RISC-dependent and sensitive to inhibition by the FHV B2 protein, as shown by the observation that B2 is essential for FHV infection of WT Drosophila cells but dispensable in cells depleted for AGO2 (12). These findings provided an example indicating an antiviral role for RNA silencing in the animal kingdom (12, 13), as has been established in higher plants (14)(15)(16)(17)(18).In this article, we report that specific RNA silencing was induced in mosquito cells in response to viral RNA replication and show that this mosquito antiviral immunity is RISCdependent and sensitive to suppression by the B2 protein encoded by either FHV or nodamura virus (NoV). We demonstrate th...

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“…NS1 deletion or truncation attenuates an influenza virus by reducing its ability to antagonize the type I IFN response [28]. It was hypothesized that this class of mutant viruses would elicit robust adaptive immune responses, despite attenuated replication, because restraints on the early innate response would be relaxed.…”

Section: Discussionmentioning

confidence: 99%

Vaccination with NS1-truncated H3N2 swine influenza virus primes T cells and confers cross-protection against an H1N1 heterosubtypic challenge in pigs

Kappes

Sandbulte

Platt

et al. 2012

Vaccine

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The diversity of contemporary swine influenza virus (SIV) strains impedes effective immunization of swine herds. Mucosally delivered, attenuated virus vaccines are one approach with potential to provide broad crossprotection. Reverse genetics-derived H3N2 SIV virus with truncated NS1 (NS1Δ126 TX98) is attenuated and immunogenic when delivered intranasally in young pigs. We analyzed T-cell priming and cross-protective efficacy in weanling piglets after intranasal inoculation with NS1Δ126 TX98 versus wild type TX98. In vivo replication of the truncation mutant was minimal compared to the wild type virus. T-cell responses were greater in magnitude in pigs infected with the wild type virus in in vitro restimulation assays. According to the expression of activation marker CD25, peripheral T cell recall responses in NS1Δ126 TX98 infected pigs were minimal. However, intracellular IFN-γ data indicate that the attenuated virus induced virus-specific CD4 + CD8 -, CD4 + CD8 + , CD4 -CD8 + , and γδ T cells within 28 days. The IFN-γ response appeared to contract, as responses were reduced at later time points prior to challenge. CD4 + CD8 + cells isolated 5 days after heterosubtypic H1N1 challenge (day 70 overall) showed an elevated CD25 response to virus restimulation. Pigs previously infected with wild type TX98 were protected from replication of the H1N1 challenge virus. Vaccination with NS1Δ126 TX98 was associated with significantly lower levels of Th1-associated cytokines in infected lungs but provided partial cross-protection against the H1N1 challenge. These results demonstrate that NS1Δ SIV vaccines can elicit cell-mediated cross-protection against antigenically divergent strains. The diversity of contemporary swine influenza virus (SIV) strains impedes effective immunization of swine herds. Mucosally delivered, attenuated virus vaccines are one approach with potential to provide broad cross-protection. Reverse genetics-derived H3N2 SIV virus with truncated NS1 (NS1 126 TX98) is attenuated and immunogenic when delivered intranasally in young pigs. We analyzed T-cell priming and cross-protective efficacy in weanling piglets after intranasal inoculation with NS1 126 TX98 versus wild type TX98. In vivo replication of the truncation mutant was minimal compared to the wild type virus. T-cell responses were greater in magnitude in pigs infected with the wild type virus in in vitro restimulation assays. According to the expression of activation marker CD25, peripheral T cell recall responses in NS1 126 TX98 infected pigs were minimal. However, intracellular IFN-␥ data indicate that the attenuated virus induced virus-specific CD4 + CD8 -, CD4 + CD8 + , CD4 -CD8 + , and ␥␦ T cells within 28 days. The IFN-␥ response appeared to contract, as responses were reduced at later time points prior to challenge. CD4 + CD8 + cells isolated 5 days after heterosubtypic H1N1 challenge (day 70 overall) showed an elevated CD25 response to virus restimulation. Pigs previously infected with wild type TX98 were protected from replicatio...

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Influenza A Virus Lacking the NS1 Gene Replicates in Interferon-Deficient Systems

Cited by 917 publications

References 32 publications

Replication fitness determines high virulence of influenza A virus in mice carrying functional Mx1 resistance gene

Replication fitness determines high virulence of influenza A virus in mice carrying functional Mx1 resistance gene

Interferon antagonist proteins of influenza and vaccinia viruses are suppressors of RNA silencing

Vaccination with NS1-truncated H3N2 swine influenza virus primes T cells and confers cross-protection against an H1N1 heterosubtypic challenge in pigs

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