scholarly journals PARP1 Enhances Influenza A Virus Propagation by Facilitating Degradation of Host Type I Interferon Receptor

2020 ◽  
Vol 94 (7) ◽  
Author(s):  
Chuan Xia ◽  
Jennifer J. Wolf ◽  
Chuankai Sun ◽  
Mengqiong Xu ◽  
Caleb J. Studstill ◽  
...  
Keyword(s):  
Innate Immunity ◽  
Influenza Virus ◽  
Molecular Mechanism ◽  
Influenza A Virus ◽  
Influenza A ◽  
Type I Interferon ◽  
Type I ◽  
Type I Ifn ◽  
Host Type ◽  
Host Innate Immunity

ABSTRACT Influenza A virus (IAV) utilizes multiple strategies to confront or evade host type I interferon (IFN)-mediated antiviral responses in order to enhance its own propagation within the host. One such strategy is to induce the degradation of type I IFN receptor 1 (IFNAR1) by utilizing viral hemagglutinin (HA). However, the molecular mechanism behind this process is poorly understood. Here, we report that a cellular protein, poly(ADP-ribose) polymerase 1 (PARP1), plays a critical role in mediating IAV HA-induced degradation of IFNAR1. We identified PARP1 as an interacting partner for IAV HA through mass spectrometry analysis. This interaction was confirmed by coimmunoprecipitation analyses. Furthermore, confocal fluorescence microscopy showed altered localization of endogenous PARP1 upon transient IAV HA expression or during IAV infection. Knockdown or inhibition of PARP1 rescued IFNAR1 levels upon IAV infection or HA expression, exemplifying the importance of PARP1 for IAV-induced reduction of IFNAR1. Notably, PARP1 was crucial for the robust replication of IAV, which was associated with regulation of the type I IFN receptor signaling pathway. These results indicate that PARP1 promotes IAV replication by controlling viral HA-induced degradation of host type I IFN receptor. Altogether, these findings provide novel insight into interactions between influenza virus and the host innate immune response and reveal a new function for PARP1 during influenza virus infection. IMPORTANCE Influenza A virus (IAV) infections cause seasonal and pandemic influenza outbreaks, which pose a devastating global health concern. Despite the availability of antivirals against influenza, new IAV strains continue to persist by overcoming the therapeutics. Therefore, much emphasis in the field is placed on identifying new therapeutic targets that can more effectively control influenza. IAV utilizes several tactics to evade host innate immunity, which include the evasion of antiviral type I interferon (IFN) responses. Degradation of type I IFN receptor (IFNAR) is one known method of subversion, but the molecular mechanism for IFNAR downregulation during IAV infection remains unclear. Here, we have found that a host protein, poly(ADP-ribose) polymerase 1 (PARP1), facilitates IFNAR degradation and accelerates IAV replication. The findings reveal a novel cellular target for the potential development of antivirals against influenza, as well as expand our base of knowledge regarding interactions between influenza and the host innate immunity.

scholarly journals Differential Type I Interferon Induction by Respiratory Syncytial Virus and Influenza A Virus In Vivo

2007 ◽  
Vol 81 (18) ◽  
pp. 9790-9800 ◽  
Author(s):  
Nancy A. Jewell ◽  
Negin Vaghefi ◽  
Sara E. Mertz ◽  
Parvis Akter ◽  
R. Stokes Peebles ◽  
...  
Keyword(s):  
Influenza Virus ◽  
Respiratory Syncytial Virus ◽  
Virus Infection ◽  
Influenza A Virus ◽  
Influenza A ◽  
Type I Interferon ◽  
Type I ◽  
Type I Ifn ◽  
Syncytial Virus

ABSTRACTType I interferon (IFN) induction is an immediate response to virus infection, and very high levels of these cytokines are produced when the Toll-like receptors (TLRs) expressed at high levels by plasmacytoid dendritic cells (pDCs) are triggered by viral nucleic acids. Unlike many RNA viruses, respiratory syncytial virus (RSV) does not appear to activate pDCs through their TLRs and it is not clear how this difference affects IFN-α/β induction in vivo. In this study, we investigated type I IFN production triggered by RSV or influenza A virus infection of BALB/c mice and found that while both viruses induced IFN-α/β production by pDCs in vitro, only influenza virus infection could stimulate type I IFN synthesis by pDCs in vivo. In situ hybridization studies demonstrated that the infected respiratory epithelium was a major source of IFN-α/β in response to either infection, but in pDC-depleted animals only type I IFN induction by influenza virus was impaired.

scholarly journals Hemagglutinin of Influenza A Virus Antagonizes Type I Interferon (IFN) Responses by Inducing Degradation of Type I IFN Receptor 1

2015 ◽  
Vol 90 (5) ◽  
pp. 2403-2417 ◽  
Author(s):  
Chuan Xia ◽  
Madhuvanthi Vijayan ◽  
Curtis J. Pritzl ◽  
Serge Y. Fuchs ◽  
Adrian B. McDermott ◽  
...  
Keyword(s):  
Signaling Pathway ◽  
Influenza A Virus ◽  
Influenza A ◽  
Type I Interferon ◽  
Innate Immune ◽  
Host Cells ◽  
Type I ◽  
Type I Ifn ◽  
Type I Ifns ◽  
Ha Protein

ABSTRACTInfluenza A virus (IAV) employs diverse strategies to circumvent type I interferon (IFN) responses, particularly by inhibiting the synthesis of type I IFNs. However, it is poorly understood if and how IAV regulates the type I IFN receptor (IFNAR)-mediated signaling mode. In this study, we demonstrate that IAV induces the degradation of IFNAR subunit 1 (IFNAR1) to attenuate the type I IFN-induced antiviral signaling pathway. Following infection, the level of IFNAR1 protein, but not mRNA, decreased. Indeed, IFNAR1 was phosphorylated and ubiquitinated by IAV infection, which resulted in IFNAR1 elimination. The transiently overexpressed IFNAR1 displayed antiviral activity by inhibiting virus replication. Importantly, the hemagglutinin (HA) protein of IAV was proved to trigger the ubiquitination of IFNAR1, diminishing the levels of IFNAR1. Further, influenza A viral HA1 subunit, but not HA2 subunit, downregulated IFNAR1. However, viral HA-mediated degradation of IFNAR1 was not caused by the endoplasmic reticulum (ER) stress response. IAV HA robustly reduced cellular sensitivity to type I IFNs, suppressing the activation of STAT1/STAT2 and induction of IFN-stimulated antiviral proteins. Taken together, our findings suggest that IAV HA causes IFNAR1 degradation, which in turn helps the virus escape the powerful innate immune system. Thus, the research elucidated an influenza viral mechanism for eluding the IFNAR signaling pathway, which could provide new insights into the interplay between influenza virus and host innate immunity.IMPORTANCEInfluenza A virus (IAV) infection causes significant morbidity and mortality worldwide and remains a major health concern. When triggered by influenza viral infection, host cells produce type I interferon (IFN) to block viral replication. Although IAV was shown to have diverse strategies to evade this powerful, IFN-mediated antiviral response, it is not well-defined if IAV manipulates the IFN receptor-mediated signaling pathway. Here, we uncovered that influenza viral hemagglutinin (HA) protein causes the degradation of type I IFN receptor subunit 1 (IFNAR1). HA promoted phosphorylation and polyubiquitination of IFNAR1, which facilitated the degradation of this receptor. The HA-mediated elimination of IFNAR1 notably decreased the cells' sensitivities to type I IFNs, as demonstrated by the diminished expression of IFN-induced antiviral genes. This discovery could help us understand how IAV regulates the host innate immune response to create an environment optimized for viral survival in host cells.

scholarly journals To Conquer the Host, Influenza Virus Is Packing It In: Interferon-Antagonistic Strategies beyond NS1

2016 ◽  
Vol 90 (19) ◽  
pp. 8389-8394 ◽  
Author(s):  
Michaela Weber-Gerlach ◽  
Friedemann Weber
Keyword(s):  
Influenza Virus ◽  
Influenza A Virus ◽  
Host Defense ◽  
Influenza A ◽  
Type I Interferon ◽  
Current Knowledge ◽  
Nonstructural Protein ◽  
Structural Proteins ◽  
Type I ◽  
Interferon System

The nonstructural protein NS1 is well established as a virulence factor of influenza A virus counteracting induction of the antiviral type I interferon system. Recent studies now show that viral structural proteins, their derivatives, and even the genome itself also contribute to keeping the host defense under control. Here, we summarize the current knowledge on these NS1-independent interferon escape strategies.

scholarly journals Differential Type I Interferon Signaling Is a Master Regulator of Susceptibility to Postinfluenza Bacterial Superinfection

mBio ◽  
2016 ◽  
Vol 7 (3) ◽  
Author(s):  
Kelly M. Shepardson ◽  
Kyle Larson ◽  
Rachelle V. Morton ◽  
Justin R. Prigge ◽  
Edward E. Schmidt ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Influenza A Virus ◽  
Virulence Factors ◽  
Influenza A ◽  
Type I Interferon ◽  
Type I ◽  
Type I Ifn ◽  
Mrsa Infection ◽  
Bacterial Superinfection ◽  
Increased Susceptibility

ABSTRACT Bacterial superinfections are a primary cause of death during influenza pandemics and epidemics. Type I interferon (IFN) signaling contributes to increased susceptibility of mice to bacterial superinfection around day 7 post-influenza A virus (IAV) infection. Here we demonstrate that the reduced susceptibility to methicillin-resistant Staphylococcus aureus (MRSA) at day 3 post-IAV infection, which we previously reported was due to interleukin-13 (IL-13)/IFN-γ responses, is also dependent on type I IFN signaling and its subsequent requirement for protective IL-13 production. We found, through utilization of blocking antibodies, that reduced susceptibility to MRSA at day 3 post-IAV infection was IFN-β dependent, whereas the increased susceptibility at day 7 was IFN-α dependent. IFN-β signaling early in IAV infection was required for MRSA clearance, whereas IFN-α signaling late in infection was not, though it did mediate increased susceptibility to MRSA at that time. Type I IFN receptor (IFNAR) signaling in CD11c + and Ly6G + cells was required for the observed reduced susceptibility at day 3 post-IAV infection. Depletion of Ly6G + cells in mice in which IFNAR signaling was either blocked or deleted indicated that Ly6G + cells were responsible for the IFNAR signaling-dependent susceptibility to MRSA superinfection at day 7 post-IAV infection. Thus, during IAV infection, the temporal differences in type I IFN signaling increased bactericidal activity of both CD11c + and Ly6G + cells at day 3 and reduced effector function of Ly6G + cells at day 7. The temporal differential outcomes induced by IFN-β (day 3) and IFN-α (day 7) signaling through the same IFNAR resulted in differential susceptibility to MRSA at 3 and 7 days post-IAV infection. IMPORTANCE Approximately 114,000 hospitalizations and 40,000 annual deaths in the United States are associated with influenza A virus (IAV) infections. Frequently, these deaths are due to community-acquired Gram-positive bacterial species, many of which show increasing resistance to antibiotic therapy. Severe complications, including parapneumonic empyema and necrotizing pneumonia, can arise, depending on virulence factors expressed by either the virus or bacteria. Unfortunately, we are unable to control the expression of these virulence factors, making host responses a logical target for therapeutic interventions. Moreover, interactions between virus, host, and bacteria that exacerbate IAV-related morbidities and mortalities are largely unknown. Here, we show that type I interferon (IFN) expression can modulate susceptibility to methicillin-resistant Staphylococcus aureus (MRSA) infection, with IFN-β reducing host susceptibility to MRSA infection while IFN-α increases susceptibility. Our data indicate that treatments designed to augment IFN-β and/or inhibit IFN-α production around day 7 post-IAV infection could reduce susceptibility to deadly superinfections.

scholarly journals Influenza Virus Evades Innate and Adaptive Immunity via the NS1 Protein

2006 ◽  
Vol 80 (13) ◽  
pp. 6295-6304 ◽  
Author(s):  
Ana Fernandez-Sesma ◽  
Svetlana Marukian ◽  
Barbara J. Ebersole ◽  
Dorothy Kaminski ◽  
Man-Seong Park ◽  
...  
Keyword(s):  
Innate Immunity ◽  
Influenza Virus ◽  
Virus Infection ◽  
Adaptive Immunity ◽  
Influenza A Virus ◽  
Influenza A ◽  
Influenza Virus Infection ◽  
Type I ◽  
Ns1 Protein ◽  
Dc Maturation

ABSTRACT Both antibodies and T cells contribute to immunity against influenza virus infection. However, the generation of strong Th1 immunity is crucial for viral clearance. Interestingly, we found that human dendritic cells (DCs) infected with influenza A virus have lower allospecific Th1-cell stimulatory abilities than DCs activated by other stimuli, such as lipopolysaccharide and Newcastle disease virus infection. This weak stimulatory activity correlates with a suboptimal maturation of the DCs following infection with influenza A virus. We next investigated whether the influenza A virus NS1 protein could be responsible for the low levels of DC maturation after influenza virus infection. The NS1 protein is an important virulence factor associated with the suppression of innate immunity via the inhibition of type I interferon (IFN) production in infected cells. Using recombinant influenza and Newcastle disease viruses, with or without the NS1 gene from influenza virus, we found that the induction of a genetic program underlying DC maturation, migration, and T-cell stimulatory activity is specifically suppressed by the expression of the NS1 protein. Among the genes affected by NS1 are those coding for macrophage inflammatory protein 1β, interleukin-12 p35 (IL-12 p35), IL-23 p19, RANTES, IL-8, IFN-α/β, and CCR7. These results indicate that the influenza A virus NS1 protein is a bifunctional viral immunosuppressor which inhibits innate immunity by preventing type I IFN release and inhibits adaptive immunity by attenuating human DC maturation and the capacity of DCs to induce T-cell responses. Our observations also support the potential use of NS1 mutant influenza viruses as live attenuated influenza virus vaccines.

scholarly journals The Clinically Approved Proteasome Inhibitor PS-341 Efficiently Blocks Influenza A Virus and Vesicular Stomatitis Virus Propagation by Establishing an Antiviral State

2010 ◽  
Vol 84 (18) ◽  
pp. 9439-9451 ◽  
Author(s):  
Sabine Eva Dudek ◽  
Christina Luig ◽  
Eva-Katharina Pauli ◽  
Ulrich Schubert ◽  
Stephan Ludwig
Keyword(s):  
Influenza Virus ◽  
Influenza A Virus ◽  
Vesicular Stomatitis Virus ◽  
Proteasome Inhibitor ◽  
Influenza A ◽  
Type I ◽  
Type I Ifn ◽  
Virus Propagation ◽  
Antiviral State ◽  
Vesicular Stomatitis

ABSTRACT Recently it has been shown that the proinflammatory NF-κB pathway promotes efficient influenza virus propagation. Based on these findings, it was suggested that NF-κB blockade may be a promising approach for antiviral intervention. The classical virus-induced activation of the NF-κB pathway requires proteasomal degradation of the inhibitor of NF-κB, IκB. Therefore, we hypothesized that inhibition of proteasomal IκB degradation should impair influenza A virus (IAV) replication. We chose the specific proteasome inhibitor PS-341, which is a clinically approved anticancer drug also known as Bortezomib or Velcade. As expected, PS-341 treatment of infected A549 cells in a concentration range that was not toxic resulted in a significant reduction of progeny virus titers. However, we could not observe the proposed suppression of NF-κB-signaling in vitro. Rather, PS-341 treatment resulted in an induction of IκB degradation and activation of NF-κB as well as the JNK/AP-1 pathway. This coincides with enhanced expression of antiviral genes, such as interleukin-6 and, most importantly, MxA, which is a strong interferon (IFN)-induced suppressor of influenza virus replication. This suggests that PS-341 may act as an antiviral agent via induction of the type I IFN response. Accordingly, PS-341 did not affect virus titers in Vero cells, which lack type I IFN genes, but strongly inhibited replication of vesicular stomatitis virus (VSV), a highly IFN-sensitive pathogen. Thus, we conclude that PS-341 blocks IAV and VSV replication by inducing an antiviral state mediated by the NF-κB-dependent expression of antivirus-acting gene products.

scholarly journals Influenza-induced type I interferon enhances susceptibility to gram-negative and gram-positive bacterial pneumonia in mice

2015 ◽  
Vol 309 (2) ◽  
pp. L158-L167 ◽  
Author(s):  
Benjamin Lee ◽  
Keven M. Robinson ◽  
Kevin J. McHugh ◽  
Erich V. Scheller ◽  
Sivanarayana Mandalapu ◽  
...  
Keyword(s):  
Influenza A Virus ◽  
Bacterial Pneumonia ◽  
Influenza A ◽  
Type I Interferon ◽  
Influenza Infection ◽  
Type I ◽  
Type I Ifn ◽  
Gram Positive ◽  
Gram Negative ◽  
Bacterial Coinfection

Suppression of type 17 immunity by type I interferon (IFN) during influenza A infection has been shown to enhance susceptibility to secondary bacterial pneumonia. Although this mechanism has been described in coinfection with gram-positive bacteria, it is unclear whether similar mechanisms may impair lung defense against gram-negative infections. Furthermore, precise delineation of the duration of type I IFN-associated susceptibility to bacterial infection remains underexplored. Therefore, we investigated the effects of preceding influenza A virus infection on subsequent challenge with the gram-negative bacteria Escherichia coli or Pseudomonas aeruginosa and the temporal association between IFN expression with susceptibility to Staphylococcus aureus challenge in a mouse model of influenza and bacterial coinfection. Here we demonstrate that preceding influenza A virus led to increased lung E. coli and P. aeruginosa bacterial burden, which was associated with suppression of type 17 immunity and attenuation of antimicrobial peptide expression. Enhanced susceptibility to S. aureus coinfection ceased at day 14 of influenza infection, when influenza-associated type I IFN levels had returned to baseline levels, further suggesting a key role for type I IFN in coinfection pathogenesis. These findings further implicate type I IFN-associated suppression of type 17 immunity and antimicrobial peptide production as a conserved mechanism for enhanced susceptibility to both gram-positive and gram-negative bacterial coinfection during influenza infection.

scholarly journals The Intestinal Microbiome Primes Host Innate Immunity Against Enteric Virus Systemic Infection Through Type I Interferon

2021 ◽  
Author(s):  
Xiao-Lian Yang ◽  
Gan Wang ◽  
Jin-Yan Xie ◽  
Han Li ◽  
Wei Liu ◽  
...  
Keyword(s):  
Innate Immunity ◽  
Type I Interferon ◽  
Systemic Infection ◽  
Enteric Virus ◽  
Encephalomyocarditis Virus ◽  
Commensal Bacteria ◽  
Intestinal Microbiome ◽  
Type I ◽  
Type I Ifn ◽  
Host Innate Immunity

Abstract BackgroundIntestinal microbiomes are of vital importance in antagonizing systemic viral infection. However, very little literature has shown whether commensal bacteria play a crucial role in protecting enteric virus systemic infection from the aspect of modulating host innate immunity. Also, only a few specific commensal bacteria species have been revealed to be capable in regulating antiviral innate immune responses mediated by type I interferon (IFN). The underlying mechanisms have not yet been elucidated.ResultsWe utilized an enteric virus, encephalomyocarditis virus (EMCV) to inoculate PBS-treated or antibiotic cocktail-administrated mice (Abx) orally or intraperitoneally to examine the impact of microbiota depletion on virulence and viral replication in vivo. Microbiota depletion exacerbated the mortality, neuropathogenesis, viremia and viral burden in brain following EMCV infection. Furthermore, Abx-treated mice exhibited severely diminished macrophage activation and impaired type I IFN production and ISG expression in PBMC, spleen or brain. With the help of fecal bacterial 16S rRNA sequencing of PBS and Abx mice, we identified a single commensal bacterium Blautia coccoides (B. coccoides) that can restore macrophage- and IFNAR-dependent type I IFN responses to restrict systemic enteric virus infection.ConclusionOur present study demonstrates that intestinal microbiome is fundamental for protecting from enteric virus systemic infection through activating macrophages and type I IFN responses. Reconstitution with B. coccoides can inhibit enteric virus infection and mitigate its neuropathogenesis by activating IFN-I and ISG responses in macrophages via IFNAR- and STAT1-mediated signaling pathway.

scholarly journals Hemagglutinin Stability Regulates H1N1 Influenza Virus Replication and Pathogenicity in Mice by Modulating Type I Interferon Responses in Dendritic Cells

2019 ◽  
Vol 94 (3) ◽  
Author(s):  
Marion Russier ◽  
Guohua Yang ◽  
Benoit Briard ◽  
Victoria Meliopoulos ◽  
Sean Cherry ◽  
...  
Keyword(s):  
Dendritic Cells ◽  
Influenza Virus ◽  
Epithelial Cell ◽  
Virus Replication ◽  
Influenza A ◽  
Type I Interferon ◽  
Influenza Vaccines ◽  
Type I ◽  
Type I Ifn ◽  
Influenza A Viruses

ABSTRACT Hemagglutinin (HA) stability, or the pH at which HA is activated to cause membrane fusion, has been associated with the replication, pathogenicity, transmissibility, and interspecies adaptation of influenza A viruses. Here, we investigated the mechanisms by which a destabilizing HA mutation, Y17H (activation pH, 6.0), attenuates virus replication and pathogenicity in DBA/2 mice compared to wild-type (WT) virus (activation pH, 5.5). The extracellular lung pH was measured to be near neutral (pH 6.9 to 7.5). WT and Y17H viruses had similar environmental stability at pH 7.0; thus, extracellular inactivation was unlikely to attenuate the Y17H virus. The Y17H virus had accelerated replication kinetics in MDCK, A549, and RAW 264.7 cells when inoculated at a multiplicity of infection (MOI) of 3 PFU/cell. The destabilizing mutation also increased early infectivity and type I interferon (IFN) responses in mouse bone marrow-derived dendritic cells (DCs). In contrast, the HA-Y17H mutation reduced virus replication in murine airway murine nasal epithelial cell and murine tracheal epithelial cell cultures and attenuated virus replication, virus spread, the severity of infection, and cellular infiltration in the lungs of mice. Normalizing virus infection and weight loss in mice by inoculating them with Y17H virus at a dose 500-fold higher than that of WT virus revealed that the destabilized mutant virus triggered the upregulation of more host genes and increased type I IFN responses and cytokine expression in DBA/2 mouse lungs. Overall, HA destabilization decreased virulence in mice by boosting early infection in DCs, resulting in the greater activation of antiviral responses, including the type I IFN response. These studies reveal that HA stability may regulate pathogenicity by modulating IFN responses. IMPORTANCE Diverse influenza A viruses circulate in wild aquatic birds, occasionally infecting farm animals. Rarely, an avian- or swine-origin influenza virus adapts to humans and starts a pandemic. Seasonal and many universal influenza vaccines target the HA surface protein, which is a key component of pandemic influenza viruses. Understanding the HA properties needed for replication and pathogenicity in mammals may guide response efforts to control influenza. Some antiviral drugs and broadly reactive influenza vaccines that target the HA protein have suffered resistance due to destabilizing HA mutations that do not compromise replicative fitness in cell culture. Here, we show that despite not compromising fitness in standard cell cultures, a destabilizing H1N1 HA stalk mutation greatly diminishes viral replication and pathogenicity in vivo by modulating type I IFN responses. This encourages targeting the HA stalk with antiviral drugs and vaccines as well as reevaluating previous candidates that were susceptible to destabilizing resistance mutations.

scholarly journals HA stability regulates H1N1 influenza virus replication and pathogenicity in mice by modulating type I interferon responses in dendritic cells

2019 ◽  
Author(s):  
Marion Russier ◽  
Guohua Yang ◽  
Benoit Briard ◽  
Victoria Meliopoulos ◽  
Sean Cherry ◽  
...  
Keyword(s):  
Dendritic Cells ◽  
Influenza Virus ◽  
Virus Replication ◽  
Influenza A ◽  
Type I Interferon ◽  
Influenza Vaccines ◽  
Type I ◽  
Type I Ifn ◽  
Influenza A Viruses ◽  
Replicative Fitness

ABSTRACTHemagglutinin (HA) stability, or the pH at which the HA is activated to cause membrane fusion, has been associated with the replicative fitness, pathogenicity, transmissibility, and interspecies adaptation of influenza A viruses. Here, we investigated several mechanisms by which a destabilizing HA mutation, Y17H (activation pH 6.0), may attenuate virus replication and pathogenicity in DBA/2 mice, compared to wild-type (WT; activation pH 5.5). Extracellular lung pH was measured to be near neutral (pH 6.9–7.5). WT and Y17H viruses had similar environmental stability at pH 7.0; thus, extracellular inactivation was unlikely to attenuate Y17H virus. The Y17H virus had accelerated single-step replication kinetics in MDCK, A549, and Raw264.7 cells. The destabilizing mutation also increased early infectivity and type I interferon (IFN) responses in mouse bone marrow–derived dendritic cells (DCs). In contrast, the HA-Y17H mutation reduced multistep replication in murine airway mNEC and mTEC cultures and attenuated virus replication, virus spread, severity of infection, and cellular infiltration in the lungs of mice. Normalizing virus infection and weight loss in mice by inoculating them with Y17H virus at a dose 500-fold higher than that of WT virus revealed that the destabilized mutant virus triggered the upregulation of more host genes and increased type I IFN responses and cytokine expression in DBA/2 mouse lungs. Overall, HA destabilization decreased virulence in mice by boosting early infection in DCs, resulting in greater activation of antiviral responses, including type I IFN. These studies reveal HA stability may regulate pathogenicity by modulating IFN responses.ImportanceDiverse influenza A viruses circulate in wild aquatic birds, occasionally infecting farm animals. Rarely, an avian- or swine-origin influenza virus adapts to humans and starts a pandemic. Seasonal and many universal influenza vaccines target the HA surface protein, which is a key component of pandemic influenza. Understanding HA properties needed for replication and pathogenicity in mammals may guide response efforts to control influenza. Some antiviral drugs and broadly reactive influenza vaccines that target the HA protein have suffered resistance due to destabilizing HA mutations that do not compromise replicative fitness in cell culture. Here, we show that despite not compromising fitness in standard cell cultures, a destabilizing H1N1 HA stalk mutation greatly diminishes viral replication and pathogenicity in vivo by modulating type I IFN responses. This encourages targeting the HA stalk with antiviral drugs and vaccines as well as reevaluating previous candidates that were susceptible to destabilizing resistance mutations.

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