Showing papers on "Influenza A virus published in 2019"
TL;DR: The differences between natural infection and vaccination in terms of the antibody responses they induce and how these responses protect against future infection are reviewed.
Abstract: The adaptive immune response to influenza virus infection is multifaceted and complex, involving antibody and cellular responses at both systemic and mucosal levels. Immune responses to natural infection with influenza virus in humans are relatively broad and long-lived, but influenza viruses can escape from these responses over time owing to their high mutation rates and antigenic flexibility. Vaccines are the best available countermeasure against infection, but vaccine effectiveness is low compared with other viral vaccines, and the induced immune response is narrow and short-lived. Furthermore, inactivated influenza virus vaccines focus on the induction of systemic IgG responses but do not effectively induce mucosal IgA responses. Here, I review the differences between natural infection and vaccination in terms of the antibody responses they induce and how these responses protect against future infection. A better understanding of how natural infection induces broad and long-lived immune responses will be key to developing next-generation influenza virus vaccines. Developing universal influenza virus vaccines will require understanding how broad and long-lived antibody responses to natural infection with influenza A virus are generated, a topic that has benefited greatly from technologies that enable the analysis of single human B cells.
367 citations
TL;DR: The host barriers that influenza A viruses of animals, especially birds, must overcome to initiate a pandemic in humans are examined and how, on crossing the species barrier, the virus mutates to establish new interactions with the human host is described.
Abstract: Influenza A viruses cause pandemics when they cross between species and an antigenically novel virus acquires the ability to infect and transmit between these new hosts. The timing of pandemics is currently unpredictable but depends on ecological and virological factors. The host range of an influenza A virus is determined by species-specific interactions between virus and host cell factors. These include the ability to bind and enter cells, to replicate the viral RNA genome within the host cell nucleus, to evade host restriction factors and innate immune responses and to transmit between individuals. In this Review, we examine the host barriers that influenza A viruses of animals, especially birds, must overcome to initiate a pandemic in humans and describe how, on crossing the species barrier, the virus mutates to establish new interactions with the human host. This knowledge is used to inform risk assessments for future pandemics and to identify virus-host interactions that could be targeted by novel intervention strategies.
321 citations
TL;DR: This review comprehensively analyzes the recent literature on how and why viral pathogenesis is altered in the obese host along with the impact of the altered host and pathogenic state on viral evolutionary dynamics in multiple models.
Abstract: With the rising prevalence of obesity has come an increasing awareness of its impact on communicable disease. As a consequence of the 2009 H1N1 influenza A virus pandemic, obesity was identified for the first time as a risk factor for increased disease severity and mortality in infected individuals. Over-nutrition that results in obesity causes a chronic state of meta-inflammation with systemic implications for immunity. Obese hosts exhibit delayed and blunted antiviral responses to influenza virus infection, and they experience poor recovery from the disease. Furthermore, the efficacy of antivirals and vaccines is reduced in this population and obesity may also play a role in altering the viral life cycle, thus complementing the already weakened immune response and leading to severe pathogenesis. Case studies and basic research in human cohorts and animal models have highlighted the prolonged viral shed in the obese host, as well as a microenvironment that permits the emergence of virulent minor variants. This review focuses on influenza A virus pathogenesis in the obese host, and on the impact of obesity on the antiviral response, viral shed, and viral evolution. We comprehensively analyze the recent literature on how and why viral pathogenesis is altered in the obese host along with the impact of the altered host and pathogenic state on viral evolutionary dynamics in multiple models. Finally, we summarized the effectiveness of current vaccines and antivirals in this populations and the questions that remain to be answered. If current trends continue, nearly 50% of the worldwide population is projected to be obese by 2050. This population will have a growing impact on both non-communicable and communicable diseases and may affect global evolutionary trends of influenza virus.
294 citations
TL;DR: The various structural features of NA are investigated, linking these with functional outcomes in viral replication and the contribution of evolving NA activity to viral attachment, entry and release of virions from infected cells, and maintenance of functional balance with the viral hemagglutinin are discussed.
Abstract: With the constant threat of emergence of a novel influenza virus pandemic, there must be continued evaluation of the molecular mechanisms that contribute to virulence. Although the influenza A virus surface glycoprotein neuraminidase (NA) has been studied mainly in the context of its role in viral release from cells, accumulating evidence suggests it plays an important, multifunctional role in virus infection and fitness. This review investigates the various structural features of NA, linking these with functional outcomes in viral replication. The contribution of evolving NA activity to viral attachment, entry and release of virions from infected cells, and maintenance of functional balance with the viral hemagglutinin are also discussed. Greater insight into the role of this important antiviral drug target is warranted.
248 citations
TL;DR: It is shown that housing Mx1 congenic mice in low relative humidity makes mice more susceptible to severe disease following respiratory challenge with influenza A virus and inhalation of dry air impairs host defense against influenza infection, reduces tissue repair, and inflicts caspase-dependent disease pathology.
Abstract: In the temperate regions, seasonal influenza virus outbreaks correlate closely with decreases in humidity. While low ambient humidity is known to enhance viral transmission, its impact on host response to influenza virus infection and disease outcome remains unclear. Here, we showed that housing Mx1 congenic mice in low relative humidity makes mice more susceptible to severe disease following respiratory challenge with influenza A virus. We find that inhalation of dry air impairs mucociliary clearance, innate antiviral defense, and tissue repair. Moreover, disease exacerbated by low relative humidity was ameliorated in caspase-1/11–deficient Mx1 mice, independent of viral burden. Single-cell RNA sequencing revealed that induction of IFN-stimulated genes in response to viral infection was diminished in multiple cell types in the lung of mice housed in low humidity condition. These results indicate that exposure to dry air impairs host defense against influenza infection, reduces tissue repair, and inflicts caspase-dependent disease pathology.
213 citations
TL;DR: Dampened activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome in bat primary immune cells in response to infection with multiple zoonotic viruses is caused by decreased transcriptional priming, the presence of a unique splice variant and an altered leucine-rich repeat domain of bat NLRP3.
Abstract: Bats are special in their ability to host emerging viruses. As the only flying mammal, bats endure high metabolic rates yet exhibit elongated lifespans. It is currently unclear whether these unique features are interlinked. The important inflammasome sensor, NLR family pyrin domain containing 3 (NLRP3), has been linked to both viral-induced and age-related inflammation. Here, we report significantly dampened activation of the NLRP3 inflammasome in bat primary immune cells compared to human or mouse counterparts. Lower induction of apoptosis-associated speck-like protein containing a CARD (ASC) speck formation and secretion of interleukin-1β in response to both 'sterile' stimuli and infection with multiple zoonotic viruses including influenza A virus (-single-stranded (ss) RNA), Melaka virus (PRV3M, double-stranded RNA) and Middle East respiratory syndrome coronavirus (+ssRNA) was observed. Importantly, this reduction of inflammation had no impact on the overall viral loads. We identified dampened transcriptional priming, a novel splice variant and an altered leucine-rich repeat domain of bat NLRP3 as the cause. Our results elucidate an important mechanism through which bats dampen inflammation with implications for longevity and unique viral reservoir status.
203 citations
TL;DR: Influenza can be found in human platelets and that platelet engulfment of influenza A results in TLR7-dependent C3 release, which in turn promotes neutrophil-DNA release and formation of platelet-DNA aggregates, demonstrating that the initial intrinsic defense against influenza is mediated by platelet–neutrophil cross-communication.
Abstract: Influenza infection increases the incidence of myocardial infarction but the reason is unknown. Platelets mediate vascular occlusion through thrombotic functions but are also recognized to have immunomodulatory activity. To determine if platelet processes are activated during influenza infection, we collected blood from 18 patients with acute influenza infection. Microscopy reveals activated platelets, many containing viral particles and extracellular-DNA associated with platelets. To understand the mechanism, we isolate human platelets and treat them with influenza A virus. Viral-engulfment leads to C3 release from platelets as a function of TLR7 and C3 leads to neutrophil-DNA release and aggregation. TLR7 specificity is confirmed in murine models lacking the receptor, and platelet depletion models support platelet-mediated C3 and neutrophil-DNA release post-influenza infection. These findings demonstrate that the initial intrinsic defense against influenza is mediated by platelet-neutrophil cross-communication that tightly regulates host immune and complement responses but can also lead to thrombotic vascular occlusion.
186 citations
TL;DR: A mosaic nanoparticle vaccine against influenza virus that is able to elicit neutralizing antibodies that span nearly 100 years of variation of influenza A virus is developed.
Abstract: The present vaccine against influenza virus has the inevitable risk of antigenic discordance between the vaccine and the circulating strains, which diminishes vaccine efficacy. This necessitates new approaches that provide broader protection against influenza. Here we designed a vaccine using the hypervariable receptor-binding domain (RBD) of viral hemagglutinin displayed on a nanoparticle (np) able to elicit antibody responses that neutralize H1N1 influenza viruses spanning over 90 years. Co-display of RBDs from multiple strains across time, so that the adjacent RBDs are heterotypic, provides an avidity advantage to cross-reactive B cells. Immunization with the mosaic RBD–np elicited broader antibody responses than those induced by an admixture of nanoparticles encompassing the same set of RBDs as separate homotypic arrays. Furthermore, we identified a broadly neutralizing monoclonal antibody in a mouse immunized with mosaic RBD–np. The mosaic antigen array signifies a unique approach that subverts monotypic immunodominance and allows otherwise subdominant cross-reactive B cell responses to emerge. Antigenic variation of influenza A viruses necessitates the annual reformulation of vaccines. Kanekiyo et al. develop a mosaic nanoparticle vaccine against influenza virus that is able to elicit neutralizing antibodies that span nearly 100 years of variation of influenza A virus.
182 citations
University of Melbourne1, Monash University, Clayton campus2, St. Jude Children's Research Hospital3, Kirby Institute4, Hokkaido University5, École Normale Supérieure6, World Health Organization7, Federation University Australia8, Monash University9, Alfred Hospital10, Royal Melbourne Hospital11, St. Vincent's Institute of Medical Research12, Royal Prince Alfred Hospital13, University of Sydney14, Garvan Institute of Medical Research15, University of New South Wales16, Cardiff University17, Australian Research Council18
TL;DR: This study introduces a new paradigm whereby CD8+ T cells confer unprecedented cross-reactivity across all influenza viruses, a key finding for the design of universal vaccines.
Abstract: Influenza A, B and C viruses (IAV, IBV and ICV, respectively) circulate globally and infect humans, with IAV and IBV causing the most severe disease. CD8+ T cells confer cross-protection against IAV strains, however the responses of CD8+ T cells to IBV and ICV are understudied. We investigated the breadth of CD8+ T cell cross-recognition and provide evidence of CD8+ T cell cross-reactivity across IAV, IBV and ICV. We identified immunodominant CD8+ T cell epitopes from IBVs that were protective in mice and found memory CD8+ T cells directed against universal and influenza-virus-type-specific epitopes in the blood and lungs of healthy humans. Lung-derived CD8+ T cells displayed tissue-resident memory phenotypes. Notably, CD38+Ki67+CD8+ effector T cells directed against novel epitopes were readily detected in IAV- or IBV-infected pediatric and adult subjects. Our study introduces a new paradigm whereby CD8+ T cells confer unprecedented cross-reactivity across all influenza viruses, a key finding for the design of universal vaccines.
166 citations
TL;DR: The discovery of a naturally occurring human antibody, FluA-20, that recognizes a new site of vulnerability on the hemagglutinin (HA) head domain and reacts with most influenza A viruses is described.
149 citations
TL;DR: Three human monoclonal antibodies isolated from an H3N2-infected donor are described that bind with exceptional breadth to multiple different influenza A and B virus neuraminidases, which neutralize the virus, mediate effector functions, are broadly protective in vivo, and inhibit neuraminidsase activity by directly binding to the active site.
Abstract: Better vaccines against influenza virus are urgently needed to provide broader protection against diverse strains, subtypes, and types. Such efforts are assisted by the identification of novel broadly neutralizing epitopes targeted by protective antibodies. Influenza vaccine development has largely focused on the hemagglutinin, but the other major surface antigen, the neuraminidase, has reemerged as a potential target for universal vaccines. We describe three human monoclonal antibodies isolated from an H3N2-infected donor that bind with exceptional breadth to multiple different influenza A and B virus neuraminidases. These antibodies neutralize the virus, mediate effector functions, are broadly protective in vivo, and inhibit neuraminidase activity by directly binding to the active site. Structural and functional characterization of these antibodies will inform the development of neuraminidase-based universal vaccines against influenza virus.
TL;DR: Study of influenza virus transmission in humans provides evidence that hemagglutinin stalk-specific antibodies correlate with protection from infection, and 50% protective titers and levels for hemagGlutination inhibition, full-length hemag glutin in, neuraminidase-inhibiting antibodies are determined.
Abstract: Influenza viruses remain a severe threat to human health, causing up to 650,000 deaths annually1,2. Seasonal influenza virus vaccines can prevent infection, but are rendered ineffective by antigenic drift. To provide improved protection from infection, novel influenza virus vaccines that target the conserved epitopes of influenza viruses, specifically those in the hemagglutinin stalk and neuraminidase, are currently being developed3. Antibodies against the hemagglutinin stalk confer protection in animal studies4–6. However, no data exist on natural infections in humans, and these antibodies do not show activity in the hemagglutination inhibition assay, the hemagglutination inhibition titer being the current correlate of protection against influenza virus infection7–9. While previous studies have investigated the protective effect of cellular immune responses and neuraminidase-inhibiting antibodies, additional serological correlates of protection from infection could aid the development of broadly protective or universal influenza virus vaccines10–13. To address this gap, we performed a household transmission study to identify alternative correlates of protection from infection and disease in naturally exposed individuals. Using this study, we determined 50% protective titers and levels for hemagglutination inhibition, full-length hemagglutinin, neuraminidase and hemagglutinin stalk-specific antibodies. Further, we found that hemagglutinin stalk antibodies independently correlated with protection from influenza virus infection. Study of influenza virus transmission in humans provides evidence that hemagglutinin stalk-specific antibodies correlate with protection from infection.
TL;DR: The effects of daily local meteorological data from Edinburgh, Scotland on the seasonal variations in viral transmission was examined and the relationship between meteorological factors and viral seasonality was investigated.
Abstract: Numerous viruses can cause upper respiratory tract infections. They often precede serious lower respiratory tract infections. Each virus has a seasonal pattern, with peaks in activity in different seasons. We examined the effects of daily local meteorological data (temperature, relative humidity, “humidity-range” and dew point) from Edinburgh, Scotland on the seasonal variations in viral transmission. We identified the seasonality of rhinovirus, adenovirus, influenza A and B viruses, human parainfluenza viruses 1–3 (HPIV), respiratory syncytial virus (RSV) and human metapneumovirus (HMPV) from the 52060 respiratory samples tested between 2009 and 2015 and then confirmed the same by a generalised linear model. We also investigated the relationship between meteorological factors and viral seasonality. Non-enveloped viruses were present throughout the year. Following logistic regression adenovirus, influenza viruses A, B, RSV and HMPV preferred low temperatures; RSV and influenza A virus preferred a narrow “humidity-range” and HPIV type 3 preferred the season with lower humidity. A change (i.e. increase or decrease) in specific meteorological factors is associated with an increase in activity of specific viruses at certain times of the year.
Rockefeller University1, Paris Descartes University2, French Institute of Health and Medical Research3, Columbia University Medical Center4, University of Texas Health Science Center at San Antonio5, Shanghai Jiao Tong University6, National Institutes of Health7, Icahn School of Medicine at Mount Sinai8, Baylor College of Medicine9, Katholieke Universiteit Leuven10
TL;DR: The authors report three unrelated children with inheritedTLR3 deficiency, impaired TLR3-dependent, IFN-α/β– and/or -λ–mediated, pulmonary epithelial cell–intrinsic immunity to influenza A virus, and life-threatening influenza pneumonitis.
Abstract: Autosomal recessive IRF7 and IRF9 deficiencies impair type I and III IFN immunity and underlie severe influenza pneumonitis. We report three unrelated children with influenza A virus (IAV) infection manifesting as acute respiratory distress syndrome (IAV-ARDS), heterozygous for rare TLR3 variants (P554S in two patients and P680L in the third) causing autosomal dominant (AD) TLR3 deficiency. AD TLR3 deficiency can underlie herpes simplex virus-1 (HSV-1) encephalitis (HSE) by impairing cortical neuron-intrinsic type I IFN immunity to HSV-1. TLR3-mutated leukocytes produce normal levels of IFNs in response to IAV. In contrast, TLR3-mutated fibroblasts produce lower levels of IFN-β and -λ, and display enhanced viral susceptibility, upon IAV infection. Moreover, the patients' iPSC-derived pulmonary epithelial cells (PECs) are susceptible to IAV. Treatment with IFN-α2b or IFN-λ1 rescues this phenotype. AD TLR3 deficiency may thus underlie IAV-ARDS by impairing TLR3-dependent, type I and/or III IFN-mediated, PEC-intrinsic immunity. Its clinical penetrance is incomplete for both IAV-ARDS and HSE, consistent with their typically sporadic nature.
TL;DR: This study provides high-resolution structures of medically relevant FluPolA, as well as insights into the replication mechanisms of the viral RNA genome, and identifies sites in Flu PolA that could be targeted in the development of antiviral drugs.
Abstract: Influenza A viruses are responsible for seasonal epidemics, and pandemics can arise from the transmission of novel zoonotic influenza A viruses to humans1,2. Influenza A viruses contain a segmented negative-sense RNA genome, which is transcribed and replicated by the viral-RNA-dependent RNA polymerase (FluPolA) composed of PB1, PB2 and PA subunits3-5. Although the high-resolution crystal structure of FluPolA of bat influenza A virus has previously been reported6, there are no complete structures available for human and avian FluPolA. Furthermore, the molecular mechanisms of genomic viral RNA (vRNA) replication-which proceeds through a complementary RNA (cRNA) replicative intermediate, and requires oligomerization of the polymerase7-10-remain largely unknown. Here, using crystallography and cryo-electron microscopy, we determine the structures of FluPolA from human influenza A/NT/60/1968 (H3N2) and avian influenza A/duck/Fujian/01/2002 (H5N1) viruses at a resolution of 3.0-4.3 A, in the presence or absence of a cRNA or vRNA template. In solution, FluPolA forms dimers of heterotrimers through the C-terminal domain of the PA subunit, the thumb subdomain of PB1 and the N1 subdomain of PB2. The cryo-electron microscopy structure of monomeric FluPolA bound to the cRNA template reveals a binding site for the 3' cRNA at the dimer interface. We use a combination of cell-based and in vitro assays to show that the interface of the FluPolA dimer is required for vRNA synthesis during replication of the viral genome. We also show that a nanobody (a single-domain antibody) that interferes with FluPolA dimerization inhibits the synthesis of vRNA and, consequently, inhibits virus replication in infected cells. Our study provides high-resolution structures of medically relevant FluPolA, as well as insights into the replication mechanisms of the viral RNA genome. In addition, our work identifies sites in FluPolA that could be targeted in the development of antiviral drugs.
TL;DR: Key findings about the 1918–1919 “Spanish” influenza pandemic are summarized and implications for current pandemic response and control are addressed, including vaccination optimization.
Abstract: The 2018-2019 period marks the centennial of the "Spanish" influenza pandemic, which caused at least 50 million deaths worldwide. The unprecedented nature of the pandemic's sudden appearance and high fatality rate serve as a stark reminder of the threat influenza poses. Unusual features of the 1918-1919 pandemic, including age-specific mortality and the high frequency of severe pneumonias, are still not fully understood. Sequencing and reconstruction of the 1918 virus has allowed scientists to answer many questions about its origin and pathogenicity, although many questions remain. This Review summarizes key findings and still-to-be answered questions about this deadliest of human events.
TL;DR: The findings indicate the possibility that azithromycin could be an effective macrolide for the treatment of human influenza, and determine the anti-influenza A(H1N1)pdm09 virus activity of azathromycin, a re-positioned macrolides antibiotic with potential as a new anti- influenza candidate.
Abstract: The pandemic influenza 2009 (A(H1N1)pdm09) virus currently causes seasonal and annual epidemic outbreaks. The widespread use of anti-influenza drugs such as neuraminidase and matrix protein 2 (M2) channel inhibitors has resulted in the emergence of drug-resistant influenza viruses. In this study, we aimed to determine the anti-influenza A(H1N1)pdm09 virus activity of azithromycin, a re-positioned macrolide antibiotic with potential as a new anti-influenza candidate, and to elucidate its underlying mechanisms of action. We performed in vitro and in vivo studies to address this. Our in vitro approaches indicated that progeny virus replication was remarkably inhibited by treating viruses with azithromycin before infection; however, azithromycin administration after infection did not affect this process. We next investigated the steps inhibited by azithromycin during virus invasion. Azithromycin did not affect attachment of viruses onto the cell surface, but blocked internalization into host cells during the early phase of infection. We further demonstrated that azithromycin targeted newly budded progeny virus from the host cells and inactivated their endocytic activity. This unique inhibitory mechanism has not been observed for other anti-influenza drugs, indicating the potential activity of azithromycin before and after influenza virus infection. Considering these in vitro observations, we administered azithromycin intranasally to mice infected with A(H1N1)pdm09 virus. Single intranasal azithromycin treatment successfully reduced viral load in the lungs and relieved hypothermia, which was induced by infection. Our findings indicate the possibility that azithromycin could be an effective macrolide for the treatment of human influenza.
TL;DR: It is shown that an average of 3.6 particles is necessary for productive infection and that coinfection supports efficient complementation within a host but not upon transmission to a new host.
Abstract: Segmentation of viral genomes into multiple RNAs creates the potential for replication of incomplete viral genomes (IVGs). Here we use a single-cell approach to quantify influenza A virus IVGs and examine their fitness implications. We find that each segment of influenza A/Panama/2007/99 (H3N2) virus has a 58% probability of being replicated in a cell infected with a single virion. Theoretical methods predict that IVGs carry high costs in a well-mixed system, as 3.6 virions are required for replication of a full genome. Spatial structure is predicted to mitigate these costs, however, and experimental manipulations of spatial structure indicate that local spread facilitates complementation. A virus entirely dependent on co-infection was used to assess relevance of IVGs in vivo. This virus grows robustly in guinea pigs, but is less infectious and does not transmit. Thus, co-infection allows IVGs to contribute to within-host spread, but complete genomes may be critical for transmission. The genome of influenza is often incomplete in infected cells, but the implications for infection remain unclear. Here, Jacobs et al. show that an average of 3.6 particles is necessary for productive infection and that coinfection supports efficient complementation within a host but not upon transmission to a new host.
TL;DR: Four compounds which inhibit polymerase function, baloxavir marboxil, favipiravir, pimodivir and AL-794 are discussed and their clinical and virological effectiveness are discussed, their propensity to select for resistance and their potential for future combination therapy with the most commonly used neuraminidase inhibitor, oseltamivir.
Nepean Hospital1, Public Health Agency of Canada2, University of Manitoba3, Harvard University4, Laurentian University5, Townsville Hospital6, Westmead Hospital7, Royal North Shore Hospital8, St Vincent Hospital9, Otto-von-Guericke University Magdeburg10, University of Tennessee11, Charles University in Prague12, University of Sydney13, University of Veterinary Medicine Vienna14
TL;DR: Transcriptomic analyses of blood from >100 influenza infected patients are provided and show that changes in circulating neutrophils are associated with severe influenza infection, providing new evidence that neutrophil-dominated host response is associated with poor outcomes.
Abstract: Severe influenza infection has no effective treatment available. One of the key barriers to developing host-directed therapy is a lack of reliable prognostic factors needed to guide such therapy. Here, we use a network analysis approach to identify host factors associated with severe influenza and fatal outcome. In influenza patients with moderate-to-severe diseases, we uncover a complex landscape of immunological pathways, with the main changes occurring in pathways related to circulating neutrophils. Patients with severe disease display excessive neutrophil extracellular traps formation, neutrophil-inflammation and delayed apoptosis, all of which have been associated with fatal outcome in animal models. Excessive neutrophil activation correlates with worsening oxygenation impairment and predicted fatal outcome (AUROC 0.817-0.898). These findings provide new evidence that neutrophil-dominated host response is associated with poor outcomes. Measuring neutrophil-related changes may improve risk stratification and patient selection, a critical first step in developing host-directed immune therapy.
TL;DR: The genesis of novel influenza A virus strains by reassortment and evolution in wild and domestic bird populations, as well as the role of wild bird migration in their long-range spread are described.
Abstract: In 1918, a strain of influenza A virus caused a human pandemic resulting in the deaths of 50 million people. A century later, with the advent of sequencing technology and corresponding phylogenetic methods, we know much more about the origins, evolution and epidemiology of influenza epidemics. Here we review the history of avian influenza viruses through the lens of their genetic makeup: from their relationship to human pandemic viruses, starting with the 1918 H1N1 strain, through to the highly pathogenic epidemics in birds and zoonoses up to 2018. We describe the genesis of novel influenza A virus strains by reassortment and evolution in wild and domestic bird populations, as well as the role of wild bird migration in their long-range spread. The emergence of highly pathogenic avian influenza viruses, and the zoonotic incursions of avian H5 and H7 viruses into humans over the last couple of decades are also described. The threat of a new avian influenza virus causing a human pandemic is still present today, although control in domestic avian populations can minimize the risk to human health. This article is part of the theme issue 'Modelling infectious disease outbreaks in humans, animals and plants: approaches and important themes'. This issue is linked with the subsequent theme issue 'Modelling infectious disease outbreaks in humans, animals and plants: epidemic forecasting and control'.
TL;DR: T-ex5 treatment produced efficient knockdown of active TMPRSS2 in all three airway cell culture models and prevented proteolytic activation and multiplication of H1N1pdm, H7N9, and H3N2 IAV in HBEC and AECII and Calu-3 cells.
Abstract: Cleavage of influenza virus hemagglutinin (HA) by host cell proteases is essential for virus infectivity and spread. We previously demonstrated in vitro that the transmembrane protease TMPRSS2 cleaves influenza A virus (IAV) and influenza B virus (IBV) HA possessing a monobasic cleavage site. Subsequent studies revealed that TMPRSS2 is crucial for the activation and pathogenesis of H1N1pdm and H7N9 IAV in mice. In contrast, activation of H3N2 IAV and IBV was found to be independent of TMPRSS2 expression and supported by an as-yet-undetermined protease(s). Here, we investigated the role of TMPRSS2 in proteolytic activation of IAV and IBV in three human airway cell culture systems: primary human bronchial epithelial cells (HBEC), primary type II alveolar epithelial cells (AECII), and Calu-3 cells. Knockdown of TMPRSS2 expression was performed using a previously described antisense peptide-conjugated phosphorodiamidate morpholino oligomer, T-ex5, that interferes with splicing of TMPRSS2 pre-mRNA, resulting in the expression of enzymatically inactive TMPRSS2. T-ex5 treatment produced efficient knockdown of active TMPRSS2 in all three airway cell culture models and prevented proteolytic activation and multiplication of H7N9 IAV in Calu-3 cells and H1N1pdm, H7N9, and H3N2 IAV in HBEC and AECII. T-ex5 treatment also inhibited the activation and spread of IBV in AECII but did not affect IBV activation in HBEC and Calu-3 cells. This study identifies TMPRSS2 as the major HA-activating protease of IAV in human airway cells and IBV in type II pneumocytes and as a potential target for the development of novel drugs to treat influenza infections.IMPORTANCE Influenza A viruses (IAV) and influenza B viruses (IBV) cause significant morbidity and mortality during seasonal outbreaks. Cleavage of the viral surface glycoprotein hemagglutinin (HA) by host proteases is a prerequisite for membrane fusion and essential for virus infectivity. Inhibition of relevant proteases provides a promising therapeutic approach that may avoid the development of drug resistance. HA of most influenza viruses is cleaved at a monobasic cleavage site, and a number of proteases have been shown to cleave HA in vitro This study demonstrates that the transmembrane protease TMPRSS2 is the major HA-activating protease of IAV in primary human bronchial cells and of both IAV and IBV in primary human type II pneumocytes. It further reveals that human and murine airway cells can differ in their HA-cleaving protease repertoires. Our data will help drive the development of potent and selective protease inhibitors as novel drugs for influenza treatment.
TL;DR: It is proposed that viral inclusions segregate vRNPs from the cytosol and facilitate selected RNA-RNA interactions in a liquid environment and likely constituting sites of assembly of epidemic and pandemic influenza genomes.
Abstract: Influenza A virus has an eight-partite RNA genome that during viral assembly forms a complex containing one copy of each RNA. Genome assembly is a selective process driven by RNA-RNA interactions and is hypothesized to lead to discrete punctate structures scattered through the cytosol. Here, we show that contrary to the accepted view, formation of these structures precedes RNA-RNA interactions among distinct viral ribonucleoproteins (vRNPs), as they assemble in cells expressing only one vRNP type. We demonstrate that these viral inclusions display characteristics of liquid organelles, segregating from the cytosol without a delimitating membrane, dynamically exchanging material and adapting fast to environmental changes. We provide evidence that viral inclusions develop close to endoplasmic reticulum (ER) exit sites, depend on continuous ER-Golgi vesicular cycling and do not promote escape to interferon response. We propose that viral inclusions segregate vRNPs from the cytosol and facilitate selected RNA-RNA interactions in a liquid environment. Influenza A virus forms cytosolic inclusions containing viral ribonucleoproteins. Here, the authors show that viral inclusions form juxtaposed the endoplasmic reticulum and have liquid properties, likely constituting sites of assembly of epidemic and pandemic influenza genomes.
TL;DR: The results suggest that influenza antibody responses shift focus with age from the mutable hemagglutinin head to other epitopes, consistent with the theory of original antigenic sin, and might affect protection.
Abstract: Influenza A viruses evolve rapidly to escape host immunity, causing reinfection. The form and duration of protection after each influenza virus infection are poorly understood. We quantify the dynamics of protective immunity by fitting individual-level mechanistic models to longitudinal serology from children and adults. We find that most protection in children but not adults correlates with antibody titers to the hemagglutinin surface protein. Protection against circulating strains wanes to half of peak levels 3.5–7 years after infection in both age groups, and wanes faster against influenza A(H3N2) than A(H1N1)pdm09. Protection against H3N2 lasts longer in adults than in children. Our results suggest that influenza antibody responses shift focus with age from the mutable hemagglutinin head to other epitopes, consistent with the theory of original antigenic sin, and might affect protection. Imprinting, or primary infection with a subtype, has modest to no effect on the risk of non-medically attended infections in adults. Protective immunity after influenza virus infection is poorly understood. Here, the authors quantify the dynamics of immunity against influenza A virus infections by fitting individual-level mechanistic models to longitudinal serology, and find that the form and dynamics of protection differ between children and adults.
TL;DR: It is demonstrated that LG2055 has prophylactic potential against RSV infection and the downregulation of SRCAP induced byLG2055 could provide new insights about the inhibition of RSV replication.
Abstract: Lactobacillus gasseri SBT2055 (LG2055) is a probiotic lactic acid bacterium with multifunctional effects, including the prevention of influenza A virus infection in mice, reduction of adipocyte size in mice, and increased lifespan in C. elegans. We investigated whether LG2055 exhibits antiviral activity against respiratory syncytial virus (RSV), a global pathogen for which a preventive strategy is required. Following oral administration of LG2055 in mice, the RSV titre in the lung was significantly decreased, while body weight was not decreased after virus infection. Additionally, the elevated expression of pro-inflammatory cytokines in the lung upon RSV infection decreased after LG2055 administration. Moreover, interferon and interferon stimulated genes were upregulated by LG2055 treatment. Comparative cellular proteomic analysis revealed that SWI2/SNF2-related CREB-binding protein activator protein (SRCAP) was a candidate for the antiviral activity of LG2055 against RSV. There was a positive correlation between the inhibition of RSV replication and the suppression of SRCAP expression and RSV replication was suppressed by SRCAP silencing. Since SRCAP is a scaffold protein to which viral non-structural proteins bind, the downregulation of SRCAP induced by LG2055 could provide new insights about the inhibition of RSV replication. In summary, our study demonstrated that LG2055 has prophylactic potential against RSV infection.
TL;DR: Progress in understanding HA/NA co-evolution as each acquires epistatic mutations to restore viral fitness to mutants selected in the other protein by host innate or adaptive immune pressure is reviewed.
Abstract: Influenza A virions possess two surface glycoproteins—the hemagglutinin (HA) and neuraminidase (NA)—which exert opposite functions. HA attaches virions to cells by binding to terminal sialic acid residues on glycoproteins/glycolipids to initiate the infectious cycle, while NA cleaves terminal sialic acids, releasing virions to complete the infectious cycle. Antibodies specific for HA or NA can protect experimental animals from IAV pathogenesis and drive antigenic variation in their target epitopes that impairs vaccine effectiveness in humans. Here, we review progress in understanding HA/NA co-evolution as each acquires epistatic mutations to restore viral fitness to mutants selected in the other protein by host innate or adaptive immune pressure. We also discuss recent exciting findings that antibodies to HA can function in vivo by blocking NA enzyme activity to prevent nascent virion release and enhance Fc receptor-based activation of innate immune cells.
TL;DR: It is shown that HA and NA are asymmetrically distributed on the surface of filamentous viruses, creating a spatial organization of binding and cleaving activities that causes viruses to step consistently away from their NA-rich pole.
Abstract: Influenza A virus (IAV) enters cells by binding to sialic acid on the cell surface. To accomplish this while avoiding immobilization by sialic acid in host mucus, viruses rely on a balance between the receptor-binding protein hemagglutinin (HA) and the receptor-cleaving protein neuraminidase (NA). Although genetic aspects of this balance are well-characterized, little is known about how the spatial organization of these proteins in the viral envelope may contribute. Using site-specific fluorescent labeling and super-resolution microscopy, we show that HA and NA are asymmetrically distributed on the surface of filamentous viruses, creating a spatial organization of binding and cleaving activities that causes viruses to step consistently away from their NA-rich pole. This Brownian ratchet-like diffusion produces persistent directional mobility that resolves the virus's conflicting needs to both penetrate mucus and stably attach to the underlying cells, potentially contributing to the prevalence of the filamentous phenotype in clinical isolates of IAV.
TL;DR: Evidence is provided that the Influenza virus protein M2 stimulates translocation of mtDNA into the cytosol in a MAVS-dependent manner and it is found that STING-dependent recognition of influenza virus is essential for limiting virus replication in vivo.
Abstract: Cytosolic mitochondrial DNA (mtDNA) activates cGAS-mediated antiviral immune responses, but the mechanism by which RNA viruses stimulate mtDNA release remains unknown. Here we show that viroporin activity of influenza virus M2 or encephalomyocarditis virus (EMCV) 2B protein triggers translocation of mtDNA into the cytosol in a MAVS-dependent manner. Although influenza virus-induced cytosolic mtDNA stimulates cGAS- and DDX41-dependent innate immune responses, the nonstructural protein 1 (NS1) of influenza virus associates with mtDNA to evade the STING-dependent antiviral immunity. The STING-dependent antiviral signaling is amplified in neighboring cells through gap junctions. In addition, we find that STING-dependent recognition of influenza virus is essential for limiting virus replication in vivo. Our results show a mechanism by which influenza virus stimulates mtDNA release and highlight the importance of DNA sensing pathway in limiting influenza virus replication.
TL;DR: The results suggest that UC-MSCs are effective in restoring alveolar fluid clearance and protein permeability in A(H5N1)-associated ALI and confer functional in addition to practical advantages over conventional bone marrow MSCs.
Abstract: Background Highly pathogenic avian influenza viruses can cause severe forms of acute lung injury (ALI) in humans, where pulmonary flooding leads to respiratory failure. The therapeutic benefits of bone marrow mesenchymal stromal cells (MSCs) have been demonstrated in a model of ALI due to influenza A(H5N1) virus. However, clinical translation is impractical and limited by a decline in efficacy as the age of the donor increases. Umbilical cord MSCs (UC-MSCs) are easier to obtain by comparison, and their primitive source may offer more-potent therapeutic effects. Methods Here we investigate the therapeutic efficacy of UC-MSCs on the mechanisms of pulmonary edema formation and alveolar fluid clearance and protein permeability of A(H5N1)-infected human alveolar epithelial cells. UC-MSCs were also tested in a mouse model of influenza ALI. Results We found that UC-MSCs were effective in restoring impaired alveolar fluid clearance and protein permeability of A(H5N1)-infected human alveolar epithelial cells. UC-MSCs consistently outperformed bone marrow MSCs, partly because of greater growth factor secretion of angiopoietin 1 and hepatocyte growth factor. Conditioned UC-MSC medium and UC-MSC exosomes were also able to recapitulate these effects. However, UC-MSCs only slightly improved survival of A(H5N1)-infected mice. Conclusions Our results suggest that UC-MSCs are effective in restoring alveolar fluid clearance and protein permeability in A(H5N1)-associated ALI and confer functional in addition to practical advantages over conventional bone marrow MSCs.
TL;DR: Aptamer RHA0385 was demonstrated to have essentially broad strain-specificity toward both recombinant hemagglutinins and the whole viruses, and the aptasensors could be applied for fast and low-cost strain-independent determination of influenza viruses.
Abstract: Highly sensitive and rapid technology of surface enhanced Raman scattering (SERS) was applied to create aptasensors for influenza virus detection. SERS achieves 106-109 times signal amplification, yielding excellent sensitivity, whereas aptamers to hemagglutinin provide a specific recognition of the influenza virus. Aptamer RHA0385 was demonstrated to have essentially broad strain-specificity toward both recombinant hemagglutinins and the whole viruses. To achieve high sensitivity, a sandwich of primary aptamers, influenza virus and secondary aptamers was assembled. Primary aptamers were attached to metal particles of a SERS substrate, and influenza viruses were captured and bound with secondary aptamers labelled with Raman-active molecules. The signal was affected by the concentration of both primary and secondary aptamers. The limit of detection was as low as 1 · 10-4 hemagglutination units per probe as tested for the H3N2 virus (A/England/42/72). Aptamer-based sensors provided recognition of various influenza viral strains, including H1, H3, and H5 hemagglutinin subtypes. Therefore, the aptasensors could be applied for fast and low-cost strain-independent determination of influenza viruses.