Necroptosis blockade prevents lung injury in severe influenza.

Severe influenza A virus (IAV) infections can result in hyper-inflammation, lung injury and acute respiratory distress syndrome1-5 (ARDS), for which there are no effective pharmacological therapies. Necroptosis is an attractive entry point for therapeutic intervention in ARDS and related inflammatory conditions because it drives pathogenic lung inflammation and lethality during severe IAV infection6-8 and can potentially be targeted by receptor interacting protein kinase 3 (RIPK3) inhibitors. Here we show that a newly developed RIPK3 inhibitor, UH15-38, potently and selectively blocked IAV-triggered necroptosis in alveolar epithelial cells in vivo. UH15-38 ameliorated lung inflammation and prevented mortality following infection with laboratory-adapted and pandemic strains of IAV, without compromising antiviral adaptive immune responses or impeding viral clearance. UH15-38 displayed robust therapeutic efficacy even when administered late in the course of infection, suggesting that RIPK3 blockade may provide clinical benefit in patients with IAV-driven ARDS and other hyper-inflammatory pathologies.

Host obesity impacts genetic variation in influenza A viral populations.

Obesity is well established as a risk factor for many noncommunicable diseases; however, its consequences for infectious disease are poorly understood. Here, we investigated the impact of host obesity on influenza A virus (IAV) genetic variation using a diet-induced obesity ferret model and the A/Hong Kong/1073/1999 (H9N2) strain. Using a co-caging study design, we investigated the maintenance, generation, and transmission of intrahost IAV genetic variation by sequencing viral genomic RNA obtained from nasal wash samples over multiple days of infection. We found evidence for an enhanced role of positive selection acting on de novo mutations in obese hosts that led to nonsynonymous changes that rose to high frequency. In addition, we identified numerous cases of mutations throughout the genome that were specific to obese hosts and that were preserved during transmission between hosts. Despite detection of obese-specific variants, the overall viral genetic diversity did not differ significantly between obese and lean hosts. This is likely due to the high supply rate of de novo variation and common evolutionary adaptations to the ferret host regardless of obesity status, which we show are mediated by variation in the hemagglutinin and polymerase genes (PB2 and PB1). We also identified defective viral genomes (DVGs) that were found uniquely in either obese or lean hosts, but the overall DVG diversity and dynamics did not differ between the two groups. Our study suggests that obesity may result in a unique selective environment impacting intrahost IAV evolution, highlighting the need for additional genetic and functional studies to confirm these effects.IMPORTANCEObesity is a chronic health condition characterized by excess adiposity leading to a systemic increase in inflammation and dysregulation of metabolic hormones and immune cell populations. Influenza A virus (IAV) is a highly infectious pathogen responsible for seasonal and pandemic influenza. Host risk factors, including compromised immunity and pre-existing health conditions, can contribute to increased infection susceptibility and disease severity. During viral replication in a host, the negative-sense single-stranded RNA genome of IAV accumulates genetic diversity that may have important consequences for viral evolution and transmission. Our study provides the first insight into the consequences of host obesity on viral genetic diversity and adaptation, suggesting that host factors associated with obesity alter the selective environment experienced by a viral population, thereby impacting the spectrum of genetic variation.

Astrovirus replication is dependent on induction of double-membrane vesicles through a PI3K-dependent, LC3-independent pathway.

Human astrovirus is a positive-sense, single-stranded RNA virus. Astrovirus infection causes gastrointestinal symptoms and can lead to encephalitis in immunocompromised patients. Positive-strand RNA viruses typically utilize host intracellular membranes to form replication organelles, which are potential antiviral targets. Many of these replication organelles are double-membrane vesicles (DMVs). Here, we show that astrovirus infection leads to an increase in DMV formation through a replication-dependent mechanism that requires some early components of the autophagy machinery. Results indicate that the upstream class III phosphatidylinositol 3-kinase (PI3K) complex, but not LC3 conjugation machinery, is utilized in DMV formation. Both chemical and genetic inhibition of the PI3K complex lead to significant reduction in DMVs, as well as viral replication. Elucidating the role of autophagy machinery in DMV formation during astrovirus infection reveals a potential target for therapeutic intervention for immunocompromised patients. IMPORTANCE These studies provide critical new evidence that astrovirus replication requires formation of double-membrane vesicles, which utilize class III phosphatidylinositol 3-kinase (PI3K), but not LC3 conjugation autophagy machinery, for biogenesis. These results are consistent with replication mechanisms for other positive-sense RNA viruses suggesting that targeting PI3K could be a promising therapeutic option for not only astrovirus, but other positive-sense RNA virus infections.

Innate Antiviral Cytokine Response to Swine Influenza Virus by Swine Respiratory Epithelial Cells.

Swine influenza virus (SIV) can cause respiratory illness in swine. Swine contribute to influenza virus reassortment, as avian, human, and/or swine influenza viruses can infect swine and reassort, and new viruses can emerge. Thus, it is important to determine the host antiviral responses that affect SIV replication. In this study, we examined the innate antiviral cytokine response to SIV by swine respiratory epithelial cells, focusing on the expression of interferon (IFN) and interferon-stimulated genes (ISGs). Both primary and transformed swine nasal and tracheal respiratory epithelial cells were examined following infection with field isolates. The results show that IFN and ISG expression is maximal at 12 h postinfection (hpi) and is dependent on cell type and virus genotype. IMPORTANCE Swine are considered intermediate hosts that have facilitated influenza virus reassortment events that have given rise pandemics or genetically related viruses have become established in swine. In this study, we examine the innate antiviral response to swine influenza virus in primary and immortalized swine nasal and tracheal epithelial cells, and show virus strain- and host cell type-dependent differential expression of key interferons and interferon-stimulated genes.

Primary Swine Respiratory Epithelial Cell Lines for the Efficient Isolation and Propagation of Influenza A Viruses.

Influenza virus isolation from clinical samples is critical for the identification and characterization of circulating and emerging viruses. Yet efficient isolation can be difficult. In these studies, we isolated primary swine nasal and tracheal respiratory epithelial cells and immortalized swine nasal epithelial cells (siNEC) and tracheal epithelial cells (siTEC) that retained the abilities to form tight junctions and cilia and to differentiate at the air-liquid interface like primary cells. Critically, both human and swine influenza viruses replicated in the immortalized cells, which generally yielded higher-titer viral isolates from human and swine nasal swabs, supported the replication of isolates that failed to grow in Madin-Darby canine kidney (MDCK) cells, and resulted in fewer dominating mutations during viral passaging than MDCK cells.IMPORTANCE Robust in vitro culture systems for influenza virus are critically needed. MDCK cells, the most widely used cell line for influenza isolation and propagation, do not adequately model the respiratory tract. Therefore, many clinical isolates, both animal and human, are unable to be isolated and characterized, limiting our understanding of currently circulating influenza viruses. We have developed immortalized swine respiratory epithelial cells that retain the ability to differentiate and can support influenza replication and isolation. These cell lines can be used as additional tools to enhance influenza research and vaccine development.

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

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.

Equine-Like H3 Avian Influenza Viruses in Wild Birds, Chile.

Since their discovery in the United States in 1963, outbreaks of infection with equine influenza virus (H3N8) have been associated with serious respiratory disease in horses worldwide. Genomic analysis suggests that equine H3 viruses are of an avian lineage, likely originating in wild birds. Equine-like internal genes have been identified in avian influenza viruses isolated from wild birds in the Southern Cone of South America. However, an equine-like H3 hemagglutinin has not been identified. We isolated 6 distinct H3 viruses from wild birds in Chile that have hemagglutinin, nucleoprotein, nonstructural protein 1, and polymerase acidic genes with high nucleotide homology to the 1963 H3N8 equine influenza virus lineage. Despite the nucleotide similarity, viruses from Chile were antigenically more closely related to avian viruses and transmitted effectively in chickens, suggesting adaptation to the avian host. These studies provide the initial demonstration that equine-like H3 hemagglutinin continues to circulate in a wild bird reservoir.

Absence of ß6 Integrin Reduces Influenza Disease Severity in Highly Susceptible Obese Mice.

Obese individuals are considered a high-risk group for developing severe influenza virus infection. While the exact mechanisms for increased disease severity remain under investigation, obese-mouse models suggest that increased acute lung injury (ALI), potentially due to enhanced viral spread and decreased wound repair, is likely involved. We previously demonstrated that upregulation of the lung epithelial cell ß6 integrin during influenza virus infection was involved in disease severity. Knocking out ß6 (ß6 KO) resulted in improved survival. Of interest, obese mice have increased lung ß6 integrin levels at homeostasis. Thus, we hypothesized that the protective effect seen in ß6 KO mice would extend to the highly susceptible obese-mouse model. In the current study, we show that crossing ß6 KO mice with genetically obese (ob/ob) mice (OBKO) resulted in reduced ALI and impaired viral spread, like their lean counterparts. Mechanistically, OBKO alveolar macrophages and epithelial cells had increased type I interferon (IFN) signaling, potentially through upregulated type I IFN receptor expression, which was important for the enhanced protection during infection. Taken together, our results indicate that the absence of an epithelial integrin can beneficially alter the pulmonary microenvironment by increasing protective type I IFN responses even in a highly susceptible obese-mouse model. These studies increase our understanding of influenza virus pathogenesis in high-risk populations and may lead to the development of novel therapies.IMPORTANCE Obesity is a risk factor for developing severe influenza virus infection. However, the reasons for this are unknown. We found that the lungs of obese mice have increased expression of the epithelial integrin ß6, a host factor associated with increased disease severity. Knocking out integrin ß6 in obese mice favorably altered the pulmonary environment by increasing type I IFN signaling, resulting in decreased viral spread, reduced lung injury, and increased survival. This study furthers our understanding of influenza virus pathogenesis in the high-risk obese population and may potentially lead to the development of novel therapies for influenza virus infection.

An Epithelial Integrin Regulates the Amplitude of Protective Lung Interferon Responses against Multiple Respiratory Pathogens.

The healthy lung maintains a steady state of immune readiness to rapidly respond to injury from invaders. Integrins are important for setting the parameters of this resting state, particularly the epithelial-restricted αVß6 integrin, which is upregulated during injury. Once expressed, αVß6 moderates acute lung injury (ALI) through as yet undefined molecular mechanisms. We show that the upregulation of ß6 during influenza infection is involved in disease pathogenesis. ß6-deficient mice (ß6 KO) have increased survival during influenza infection likely due to the limited viral spread into the alveolar spaces leading to reduced ALI. Although the ß6 KO have morphologically normal lungs, they harbor constitutively activated lung CD11b+ alveolar macrophages (AM) and elevated type I IFN signaling activity, which we traced to the loss of ß6-activated transforming growth factor-ß (TGF-ß). Administration of exogenous TGF-ß to ß6 KO mice leads to reduced numbers of CD11b+ AMs, decreased type I IFN signaling activity and loss of the protective phenotype during influenza infection. Protection extended to other respiratory pathogens such as Sendai virus and bacterial pneumonia. Our studies demonstrate that the loss of one epithelial protein, αVß6 integrin, can alter the lung microenvironment during both homeostasis and respiratory infection leading to reduced lung injury and improved survival.

Swine Influenza Virus (H1N2) Characterization and Transmission in Ferrets, Chile.

Phylogenetic analysis of the influenza hemagglutinin gene (HA) has suggested that commercial pigs in Chile harbor unique human seasonal H1-like influenza viruses, but further information, including characterization of these viruses, was unavailable. We isolated influenza virus (H1N2) from a swine in a backyard production farm in Central Chile and demonstrated that the HA gene was identical to that in a previous report. Its HA and neuraminidase genes were most similar to human H1 and N2 viruses from the early 1990s and internal segments were similar to influenza A(H1N1)pdm09 virus. The virus replicated efficiently in vitro and in vivo and transmitted in ferrets by respiratory droplet. Antigenically, it was distinct from other swine viruses. Hemagglutination inhibition analysis suggested that antibody titers to the swine Chilean H1N2 virus were decreased in persons born after 1990. Further studies are needed to characterize the potential risk to humans, as well as the ecology of influenza in swine in South America.

Reversion of Cold-Adapted Live Attenuated Influenza Vaccine into a Pathogenic Virus.

UNLABELLED: The only licensed live attenuated influenza A virus vaccines (LAIVs) in the United States (FluMist) are created using internal protein-coding gene segments from the cold-adapted temperature-sensitive master donor virus A/Ann Arbor/6/1960 and HA/NA gene segments from circulating viruses. During serial passage of A/Ann Arbor/6/1960 at low temperatures to select the desired attenuating phenotypes, multiple cold-adaptive mutations and temperature-sensitive mutations arose. A substantial amount of scientific and clinical evidence has proven that FluMist is safe and effective. Nevertheless, no study has been conducted specifically to determine if the attenuating temperature-sensitive phenotype can revert and, if so, the types of substitutions that will emerge (i.e., compensatory substitutions versus reversion of existing attenuating mutations). Serial passage of the monovalent FluMist 2009 H1N1 pandemic vaccine at increasing temperatures in vitro generated a variant that replicated efficiently at higher temperatures. Sequencing of the variant identified seven nonsynonymous mutations, PB1-E51K, PB1-I171V, PA-N350K, PA-L366I, NP-N125Y, NP-V186I, and NS2-G63E. None occurred at positions previously reported to affect the temperature sensitivity of influenza A viruses. Synthetic genomics technology was used to synthesize the whole genome of the virus, and the roles of individual mutations were characterized by assessing their effects on RNA polymerase activity and virus replication kinetics at various temperatures. The revertant also regained virulence and caused significant disease in mice, with severity comparable to that caused by a wild-type 2009 H1N1 pandemic virus. IMPORTANCE: The live attenuated influenza vaccine FluMist has been proven safe and effective and is widely used in the United States. The phenotype and genotype of the vaccine virus are believed to be very stable, and mutants that cause disease in animals or humans have never been reported. By propagating the virus under well-controlled laboratory conditions, we found that the FluMist vaccine backbone could regain virulence to cause severe disease in mice. The identification of the responsible substitutions and elucidation of the underlying mechanisms provide unique insights into the attenuation of influenza virus, which is important to basic research on vaccines, attenuation reversion, and replication. In addition, this study suggests that the safety of LAIVs should be closely monitored after mass vaccination and that novel strategies to continue to improve LAIV vaccine safety should be investigated.

Diverse heterologous primary infections radically alter immunodominance hierarchies and clinical outcomes following H7N9 influenza challenge in mice.

The recent emergence of a novel H7N9 influenza A virus (IAV) causing severe human infections in China raises concerns about a possible pandemic. The lack of pre-existing neutralizing antibodies in the broader population highlights the potential protective role of IAV-specific CD8(+) cytotoxic T lymphocyte (CTL) memory specific for epitopes conserved between H7N9 and previously encountered IAVs. In the present study, the heterosubtypic immunity generated by prior H9N2 or H1N1 infections significantly, but variably, reduced morbidity and mortality, pulmonary virus load and time to clearance in mice challenged with the H7N9 virus. In all cases, the recall of established CTL memory was characterized by earlier, greater airway infiltration of effectors targeting the conserved or cross-reactive H7N9 IAV peptides; though, depending on the priming IAV, each case was accompanied by distinct CTL epitope immunodominance hierarchies for the prominent K(b)PB(1703, D(b)PA(224), and D(b)NP(366) epitopes. While the presence of conserved, variable, or cross-reactive epitopes between the priming H9N2 and H1N1 and the challenge H7N9 IAVs clearly influenced any change in the immunodominance hierarchy, the changing patterns were not tied solely to epitope conservation. Furthermore, the total size of the IAV-specific memory CTL pool after priming was a better predictor of favorable outcomes than the extent of epitope conservation or secondary CTL expansion. Modifying the size of the memory CTL pool significantly altered its subsequent protective efficacy on disease severity or virus clearance, confirming the important role of heterologous priming. These findings establish that both the protective efficacy of heterosubtypic immunity and CTL immunodominance hierarchies are reflective of the immunological history of the host, a finding that has implications for understanding human CTL responses and the rational design of CTL-mediated vaccines.

Influenza promotes collagen deposition via αvß6 integrin-mediated transforming growth factor ß activation.

Influenza infection exacerbates chronic pulmonary diseases, including idiopathic pulmonary fibrosis. A central pathway in the pathogenesis of idiopathic pulmonary fibrosis is epithelial injury leading to activation of transforming growth factor ß (TGFß). The mechanism and functional consequences of influenza-induced activation of epithelial TGFß are unclear. Influenza stimulates toll-like receptor 3 (TLR3), which can increase RhoA activity, a key event prior to activation of TGFß by the αvß6 integrin. We hypothesized that influenza would stimulate TLR3 leading to activation of latent TGFß via αvß6 integrin in epithelial cells. Using H1152 (IC50 6.1 µm) to inhibit Rho kinase and 6.3G9 to inhibit αvß6 integrins, we demonstrate their involvement in influenza (A/PR/8/34 H1N1) and poly(I:C)-induced TGFß activation. We confirm the involvement of TLR3 in this process using chloroquine (IC50 11.9 µm) and a dominant negative TLR3 construct (pZERO-hTLR3). Examination of lungs from influenza-infected mice revealed augmented levels of collagen deposition, phosphorylated Smad2/3, αvß6 integrin, and apoptotic cells. Finally, we demonstrate that αvß6 integrin-mediated TGFß activity following influenza infection promotes epithelial cell death in vitro and enhanced collagen deposition in vivo and that this response is diminished in Smad3 knock-out mice. These data show that H1N1 and poly(I:C) can induce αvß6 integrin-dependent TGFß activity in epithelial cells via stimulation of TLR3 and suggest a novel mechanism by which influenza infection may promote collagen deposition in fibrotic lung disease.

Human H7N9 and H5N1 influenza viruses differ in induction of cytokines and tissue tropism.

UNLABELLED: Since emerging in 2013, the avian-origin H7N9 influenza viruses have resulted in over 400 human infections, leading to 115 deaths to date. Although the epidemiology differs from human highly pathogenic avian H5N1 influenza virus infections, there is a similar rapid progression to acute respiratory distress syndrome. The aim of these studies was to compare the pathological and immunological characteristics of a panel of human H7N9 and H5N1 viruses in vitro and in vivo. Although there were similarities between particular H5N1 and H7N9 viruses, including association between lethal disease and spread to the alveolar spaces and kidney, there were also strain-specific differences. Both H5N1 and H7N9 viruses are capable of causing lethal infections, with mortality correlating most strongly with wider distribution of viral antigen in the lungs, rather than with traditional measures of virus titer and host responses. Strain-specific differences included hypercytokinemia in H5N1 infections that was not seen with the H7N9 infections regardless of lethality. Conversely, H7N9 viruses showed a greater tropism for respiratory epithelium covering nasal passages and nasopharynx-associated lymphoid tissue than H5N1 viruses, which may explain the enhanced transmission in ferret models. Overall, these studies highlight some distinctive properties of H5N1 and H7N9 viruses in different in vitro and in vivo models. IMPORTANCE: The novel avian-origin H7N9 pandemic represents a serious threat to public health. The ability of H7N9 to cause serious lung pathology, leading in some cases to the development of acute respiratory distress syndrome, is of particular concern. Initial reports of H7N9 infection compared them to infections caused by highly pathogenic avian (HPAI) H5N1 viruses. Thus, it is of critical importance to understand the pathology and immunological response to infection with H7N9 compared to HPAI H5N1 viruses. We compared these responses in both in vitro and in vivo models, and found that H5N1 and H7N9 infections exhibit distinct pathological, immunological, and tissue tropism differences that could explain differences in clinical disease and viral transmission.

Establishment of Swine Primary Nasal, Tracheal, and Bronchial Epithelial Cell Culture Models for the Study of Influenza Virus Infection.

We established primary porcine nasal, tracheal, and bronchial epithelial cells that recapitulate the physical and functional properties of the respiratory tract and have the ability to fully differentiate. Trans-well cultures demonstrated increased transepithelial electrical resistance over time the presence of tight junctions as demonstrated by immunohistochemistry. The nasal, tracheal, and bronchial epithelial cells developed cilia, secreted mucus, and expressed sialic acids on surface glycoproteins, the latter which are required for influenza A virus infection. Swine influenza viruses were shown to replicate efficiently in the primary epithelial cell cultures, supporting the use of these culture models to assess swine influenza and other virus infection. Primary porcine nasal, tracheal, and bronchial epithelial cell culture models enable assessment of emerging and novel influenza viruses for pandemic potential as well as mechanistic studies to understand mechanisms of infection, reassortment, and generation of novel virus. As swine are susceptible to infection with multiple viral and bacterial respiratory pathogens, these primary airway cell models may enable study of the cellular response to infection by pathogens associated with Porcine Respiratory Disease Complex.

Inactivated influenza virus vaccines expressing COBRA hemagglutinin elicited broadly reactive, long-lived protective antibodies.

The influenza viruses cause seasonal respiratory illness that affect millions of people globally every year. Prophylactic vaccines are the recommended method to prevent the breakout of influenza epidemics. One of the current commercial influenza vaccines consists of inactivated viruses that are selected months prior to the start of a new influenza season. In many seasons, the vaccine effectiveness (VE) of these vaccines can be relatively low. Therefore, there is an urgent need to develop an improved, more universal influenza vaccine (UIV) that can provide broad protection against various drifted strains in all age groups. To meet this need, the computationally optimized broadly reactive antigen (COBRA) methodology was developed to design a hemagglutinin (HA) molecule as a new influenza vaccine. In this study, COBRA HA-based inactivated influenza viruses (IIV) expressing the COBRA HA from H1 or H3 influenza viruses were developed and characterized for the elicitation of immediate and long-term protective immunity in both immunologically naïve or influenza pre-immune animal models. These results were compared to animals vaccinated with IIV vaccines expressing wild-type H1 or H3 HA proteins (WT-IIV). The COBRA-IIV elicited long-lasting broadly reactive antibodies that had hemagglutination-inhibition (HAI) activity against drifted influenza variants.

Diet-induced obesity affects influenza disease severity and transmission dynamics in ferrets.

Obesity, and the associated metabolic syndrome, is a risk factor for increased disease severity with a variety of infectious agents, including influenza virus. Yet, the mechanisms are only partially understood. As the number of people, particularly children, living with obesity continues to rise, it is critical to understand the role of host status on disease pathogenesis. In these studies, we use a diet-induced obese ferret model and tools to demonstrate that, like humans, obesity resulted in notable changes to the lung microenvironment, leading to increased clinical disease and viral spread to the lower respiratory tract. The decreased antiviral responses also resulted in obese animals shedding higher infectious virus for a longer period, making them more likely to transmit to contacts. These data suggest that the obese ferret model may be crucial to understanding obesity's impact on influenza disease severity and community transmission and a key tool for therapeutic and intervention development for this high-risk population.

Interaction between host G3BP and viral nucleocapsid protein regulates SARS-CoV-2 replication and pathogenicity.

G3BP1/2 are paralogous proteins that promote stress granule formation in response to cellular stresses, including viral infection. The nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inhibits stress granule assembly and interacts with G3BP1/2 via an ITFG motif, including residue F17, in the N protein. Prior studies examining the impact of the G3PB1-N interaction on SARS-CoV-2 replication have produced inconsistent findings, and the role of this interaction in pathogenesis is unknown. Here, we use structural and biochemical analyses to define the residues required for G3BP1-N interaction and structure-guided mutagenesis to selectively disrupt this interaction. We find that N-F17A mutation causes highly specific loss of interaction with G3BP1/2. SARS-CoV-2 N-F17A fails to inhibit stress granule assembly in cells, has decreased viral replication, and causes decreased pathology in vivo. Further mechanistic studies indicate that the N-F17-mediated G3BP1-N interaction promotes infection by limiting sequestration of viral genomic RNA (gRNA) into stress granules.

Host gene targets for novel influenza therapies elucidated by high-throughput RNA interference screens.

Influenza virus encodes only 11 viral proteins but replicates in a broad range of avian and mammalian species by exploiting host cell functions. Genome-wide RNA interference (RNAi) has proven to be a powerful tool for identifying the host molecules that participate in each step of virus replication. Meta-analysis of findings from genome-wide RNAi screens has shown influenza virus to be dependent on functional nodes in host cell pathways, requiring a wide variety of molecules and cellular proteins for replication. Because rapid evolution of the influenza A viruses persistently complicates the effectiveness of vaccines and therapeutics, a further understanding of the complex host cell pathways coopted by influenza virus for replication may provide new targets and strategies for antiviral therapy. RNAi genome screening technologies together with bioinformatics can provide the ability to rapidly identify specific host factors involved in resistance and susceptibility to influenza virus, allowing for novel disease intervention strategies.