Molecular mechanisms of interspecies transmission and pathogenicity of influenza viruses: Lessons from the 2009 pandemic

Immunomodulatory and antiviral effects of Lycium barbarum glycopeptide on influenza a virus infection

Influenza is caused by a respiratory virus and has a major global impact on human health. Influenza A viruses in particular are highly pathogenic to humans and have caused multiple pandemics. An important consequence of infection is viral pneumonia, and with serious complications of excessive inflammation and tissue damage. Therefore, simultaneously reducing direct damage caused by virus infection and relieving indirect damage caused by excessive inflammation would be an effective treatment strategy. Lycium barbarum glycopeptide (LbGp) is a mixture of five highly branched polysaccharide-protein conjuncts (LbGp1-5) isolated from Lycium barbarum fruit. LbGp has pro-immune activity that is 1-2 orders of magnitude stronger than that of other plant polysaccharides. However, there are few reports on the immunomodulatory and antiviral activities of LbGp. In this study, we evaluated the antiviral and immunomodulatory effects of LbGp in vivo and in vitro and investigated its therapeutic effect on H1N1-induced viral pneumonia and mechanisms of action. In vitro, cytokine secretion, NF-κB p65 nuclear translocation, and CD86 mRNA expression in LPS-stimulated RAW264.7 cells were constrained by LbGp treatment. In A549 cells, LbGp can inhibit H1N1 infection by blocking virus attachment and entry action. In vivo experiments confirmed that administration of LbGp can effectively increase the survival rate, body weight and decrease the lung index of mice infected with H1N1. Compared to the model group, pulmonary histopathologic symptoms in lung sections of mice treated with LbGp were obviously alleviated. Further investigation revealed that the mechanism of LbGp in the treatment of H1N1-induced viral pneumonia includes reducing the viral load in lung, regulating the phenotype of pulmonary macrophages, and inhibiting excessive inflammation. In conclusion, LbGp exhibits potential curative effects against H1N1-induced viral pneumonia in mice, and these effects are associated with its good immuno-regulatory and antiviral activities.

A public-private partnership for the express development of antiviral leads: a perspective view

INTRODUCTION

The COVID-19 pandemic raises the question of strategic readiness for emergent pathogens. The current case illustrates that the cost of inaction can be higher in the future. The perspective article proposes a dedicated, government-sponsored agency developing anti-viral leads against all potentially dangerous pathogen species.

AREAS COVERED

The author explores the methods of computational drug screening and in-silico synthesis and proposes a specialized government-sponsored agency focusing on leads and functioning in collaboration with a network of labs, pharma, biotech firms, and academia, in order to test each lead against multiple viral species. The agency will employ artificial intelligence and machine learning tools to cut the costs further. The algorithms are expected to receive continuous feedback from the network of partners conducting the tests.

EXPERT OPINION

The author proposes a bionic principle, emulating antibody response by producing a combinatorial diversity of high q uality generic antiviral leads, suitable for multiple potentially emerging species. The availability of multiple pre-tested agents and an even greater number of combinations would reduce the impact of the next outbreak. The methodologies developed in this effort are likely to find utility in the design of chronic disease therapeutics.

Alternative interaction sites in the influenza A virus nucleoprotein mediate viral escape from the importin-α7 mediated nuclear import pathway

Influenza A viruses are able to adapt to restrictive conditions due to their high mutation rates. Importin-α7 is a component of the nuclear import machinery required for avian-mammalian adaptation and replicative fitness in human cells. Here, we elucidate the mechanisms by which influenza A viruses may escape replicative restriction in the absence of importin-α7. To address this question, we assessed viral evolution in mice lacking the importin-α7 gene. We show that three mutations in particular occur with high frequency in the viral nucleoprotein (NP) protein (G102R, M105K and D375N) in a specific structural area upon in vivo adaptation. Moreover, our findings suggest that the adaptive NP mutations mediate viral escape from importin-α7 requirement likely due to the utilization of alternative interaction sites in NP beyond the classical nuclear localization signal. However, viral escape from importin-α7 by mutations in NP is, at least in part, associated with reduced viral replication highlighting the crucial contribution of importin-α7 to replicative fitness in human cells.

Mutation of Influenza A Virus PA-X Decreases Pathogenicity in Chicken Embryos and Can Increase the Yield of Reassortant Candidate Vaccine Viruses

Influenza A virus is a widespread pathogen that affects both humans and a variety of animal species, causing regular epidemics and sporadic pandemics, with major public health and economic consequences. A better understanding of virus biology is therefore important. The primary control measure is vaccination, which for humans mostly relies on antigens produced in eggs from PR8-based viruses bearing the glycoprotein genes of interest. However, not all reassortants replicate well enough to supply sufficient virus antigen for demand. The significance of our research lies in identifying that mutation of the PA-X gene in the PR8 strain of virus can improve antigen yield, potentially by decreasing the pathogenicity of the virus in embryonated eggs.

The PA-X protein of influenza A virus has roles in host cell shutoff and viral pathogenesis. While most strains are predicted to encode PA-X, strain-dependent variations in activity have been noted. We found that PA-X protein from the A/PR/8/34 (PR8) strain had significantly lower repressive activity against cellular gene expression than PA-X proteins from the avian strains A/turkey/England/50-92/91 (H5N1) (T/E) and A/chicken/Rostock/34 (H7N1). Loss of normal PA-X expression, either by mutation of the frameshift site or by truncating the X open reading frame (ORF), had little effect on the infectious virus titer of PR8 or PR8 7:1 reassortants with T/E segment 3 grown in embryonated hens’ eggs. However, in both virus backgrounds, mutation of PA-X led to decreased embryo mortality and lower overall pathology, effects that were more pronounced in the PR8 strain than in the T/E reassortant, despite the low shutoff activity of the PR8 PA-X. Purified PA-X mutant virus particles displayed an increased ratio of hemagglutinin (HA) to nucleoprotein (NP) and M1 compared to values for their wild-type (WT) counterparts, suggesting altered virion composition. When the PA-X gene was mutated in the background of poorly growing PR8 6:2 vaccine reassortant analogues containing the HA and neuraminidase (NA) segments from H1N1 2009 pandemic viruses or from an avian H7N3 strain, HA yield increased up to 2-fold. This suggests that the PR8 PA-X protein may harbor a function unrelated to host cell shutoff and that disruption of the PA-X gene has the potential to improve the HA yield of vaccine viruses.

IMPORTANCE Influenza A virus is a widespread pathogen that affects both humans and a variety of animal species, causing regular epidemics and sporadic pandemics, with major public health and economic consequences. A better understanding of virus biology is therefore important. The primary control measure is vaccination, which for humans mostly relies on antigens produced in eggs from PR8-based viruses bearing the glycoprotein genes of interest. However, not all reassortants replicate well enough to supply sufficient virus antigen for demand. The significance of our research lies in identifying that mutation of the PA-X gene in the PR8 strain of virus can improve antigen yield, potentially by decreasing the pathogenicity of the virus in embryonated eggs.

Sheng Jiang San, a traditional multi-herb formulation, exerts anti-influenza effects in vitro and in vivo via neuraminidase inhibition and immune regulation

Background

Sheng Jiang San (SJS), a multi-herb formulation, is used in treating high fever, thirsty and anxiety in ancient China and it is sometimes used to treat seasonal influenza nowadays. However, there is no evidence-based investigation and mechanism research to support the anti-influenza efficacy of SJS. This study aims at evaluating the anti-influenza effect of SJS and investigating its possible mechanism.

Methods

The inhibitory effect of SJS against different influenza virus strains on MDCK cells was examined. Influenza virus infected BALB/c mice were employed to evaluate the efficacy as in vivo model. Mice challenged with A/PR/8/34 (H1N1) were orally administrated 1 g/kg/day of SJS for seven days and monitored for 14 days. The survival rate, body weight changes, lung index, lung viral load, histopathologic changes and immune regulation of the mice were measured. The underlying anti-influenza virus mechanism of SJS was studied by a series of biological assays to determine if hemagglutinin, ribonucleoprotein complex or neuraminidase were targets of SJS.

Results

Results showed SJS exerted a broad-spectrum of inhibitory effects on multiple influenza strains in a dose-dependent manner. IC₅₀ of SJS against A/WSN/33 (H1N1) was lower than 35 μg/ml. SJS also protected 50% of mice from A/PR/8/34 (H1N1) infection. The lung index and the lung viral load of SJS treated mice were significantly decreased compared with untreated mice. Meanwhile, SJS targeted on neuraminidase of influenza virus as SJS at 2 mg/ml inhibited 80% of neuraminidase enzymatic activity. SJS also significantly down-regulated TNF-α and up-regulated IL-2 of influenza virus induced mice.

Conclusions

Thus, SJS is a useful formulation for treating influenza virus infection.

Electronic supplementary material

The online version of this article (10.1186/s12906-018-2216-7) contains supplementary material, which is available to authorized users.

Eliciting unnatural immune responses by activating cryptic epitopes in viral antigens

Antigenic variation in viral surface antigens is a strategy for escaping the host's adaptive immunity, whereas regions with pivotal functions for infection are less subject to antigenic variability. We hypothesized that genetically invariable and immunologically dormant regions of a viral surface antigen could be exposed to the host immune system and activated by rendering them susceptible to antigen-processing machinery in professional antigen-presenting cells (APCs). Considering the frequent antigen drift and shift in influenza viruses, we identified and used structural modeling to evaluate the conserved regions on the influenza hemagglutinin (HA) surface as potential epitopes. Mutant viruses containing the cleavage motifs of cathepsin S within HA were generated. Immunization of mice showed that the mutant, but not the wild-type virus, elicited specific antibodies against the cryptic epitope. Those antibodies were purified, and specific binding to HA was confirmed. These results suggest that an unnatural immune response can be elicited through the processing of target antigens in APCs, followed by presentation via the major histocompatibility complex, if not subjected to regulatory pathways. By harnessing the antigen-processing machinery, our study shows a proof-of-principle for designer vaccines with increased efficacy and safety by either activating cryptic, or inactivating naturally occurring, epitopes of viral antigens.-Lee, Y. J., Yu, J. E., Kim, P., Lee, J.-Y., Cheong, Y. C., Lee, Y. J., Chang, J., Seong, B. L. Eliciting unnatural immune responses by activating cryptic epitopes in viral antigens.

The Chinese prescription lianhuaqingwen capsule exerts anti-influenza activity through the inhibition of viral propagation and impacts immune function

Background

Lianhuaqingwen Capsule (LH-C) is a traditional Chinese medicine (TCM) formula used to treat respiratory tract infectious diseases in Chinese. The aim of this study was to determine the antiviral activity of LH-C and its immunomodulatory effects on viral infection.

Method

The in vitro cytotoxicity and antiviral activity of LH-C was determined by MTT and Plaque reduction assays. Time course study under single-cycle virus growth conditions were used to determine which stage of viral replication was blocked. The effect of LH-C on the nuclear export of the viral nucleoprotein was examined using an indirect immunofluorescence assay. The regulation to different signaling transduction events and cytokine/chemokine expression of LH-C was evaluated using Western blotting and real-time RT-PCR. After virus inoculation, BALB/c mice were administered with LH-C of different concentrations for 5 days. Body-weight, viral titers and lung pathology of the mice were measured, the level of inflammatory cytokines were also examined using real-time RT-PCR.

Results

LH-C inhibited the proliferation of influenza viruses of various strain in vitro, with the 50% inhibitory concentration (IC₅₀) ranging from 0.35 to 2 mg/mL. LH-C blocked the early stages (0–2 h) of virus infection, it also suppressed virus-induced NF-kB activation and alleviated virus-induced gene expression of IL-6, IL-8, TNF-a, IP-10, and MCP-1 in a dose-dependent manner. LH-C treatment efficiently impaired the nuclear export of the viral RNP. A decrease of the viral titers in the lungs of mice were observed in groups administered with LH-C. The level of inflammatory cytokines were also decreased in the early stages of infection.

Conclusions

LH-C, as a TCM prescription, exerts broad-spectrum effects on a series of influenza viruses, including the newly emerged H7N9, and particularly regulates the immune response of virus infection. Thus, LH-C might be a promising option for treating influenza virus infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-017-1585-7) contains supplementary material, which is available to authorized users.

The Chinese prescription lianhuaqingwen capsule exerts anti-influenza activity through the inhibition of viral propagation and impacts immune function

BACKGROUND

Lianhuaqingwen Capsule (LH-C) is a traditional Chinese medicine (TCM) formula used to treat respiratory tract infectious diseases in Chinese. The aim of this study was to determine the antiviral activity of LH-C and its immunomodulatory effects on viral infection.

METHOD

The in vitro cytotoxicity and antiviral activity of LH-C was determined by MTT and Plaque reduction assays. Time course study under single-cycle virus growth conditions were used to determine which stage of viral replication was blocked. The effect of LH-C on the nuclear export of the viral nucleoprotein was examined using an indirect immunofluorescence assay. The regulation to different signaling transduction events and cytokine/chemokine expression of LH-C was evaluated using Western blotting and real-time RT-PCR. After virus inoculation, BALB/c mice were administered with LH-C of different concentrations for 5 days. Body-weight, viral titers and lung pathology of the mice were measured, the level of inflammatory cytokines were also examined using real-time RT-PCR.

RESULTS

LH-C inhibited the proliferation of influenza viruses of various strain in vitro, with the 50% inhibitory concentration (IC50) ranging from 0.35 to 2 mg/mL. LH-C blocked the early stages (0-2 h) of virus infection, it also suppressed virus-induced NF-kB activation and alleviated virus-induced gene expression of IL-6, IL-8, TNF-a, IP-10, and MCP-1 in a dose-dependent manner. LH-C treatment efficiently impaired the nuclear export of the viral RNP. A decrease of the viral titers in the lungs of mice were observed in groups administered with LH-C. The level of inflammatory cytokines were also decreased in the early stages of infection.

CONCLUSIONS

LH-C, as a TCM prescription, exerts broad-spectrum effects on a series of influenza viruses, including the newly emerged H7N9, and particularly regulates the immune response of virus infection. Thus, LH-C might be a promising option for treating influenza virus infection.

H7N9 Influenza A Virus Exhibits Importin-α7-Mediated Replication in the Mammalian Respiratory Tract

The acute respiratory distress syndrome (ARDS) is the leading cause of death in influenza A virus (IAV)-infected patients. Hereby, the cellular importin-α7 gene plays a major role. It promotes viral replication in the lung, thereby increasing the risk for the development of pneumonia complicated by ARDS. Herein, we analyzed whether the recently emerged H7N9 avian IAV has already adapted to human importin-α7 use, which is associated with high-level virus replication in the mammalian lung. Using a cell-based viral polymerase activity assay, we could detect a decreased H7N9 IAV polymerase activity when importin-α7 was silenced by siRNA. Moreover, virus replication was diminished in the murine cells lacking the importin-α7 gene. Consistently, importin-α7 knockout mice presented reduced pulmonary virus titers and lung lesions as well as enhanced survival rates compared to wild-type mice. In summary, our results show that H7N9 IAV have acquired distinct features of adaptation to human host factors that enable enhanced virulence in mammals. In particular, adaptation to human importin-α7 mediates elevated virus replication in the mammalian lung, which might have contributed to ARDS observed in H7N9-infected patients.

Respiratory Mucosal Proteome Quantification in Human Influenza Infections

Respiratory influenza virus infections represent a serious threat to human health. Underlying medical conditions and genetic make-up predispose some influenza patients to more severe forms of disease. To date, only a few studies have been performed in patients to correlate a selected group of cytokines and chemokines with influenza infection. Therefore, we evaluated the potential of a novel multiplex micro-proteomics technology, SOMAscan, to quantify proteins in the respiratory mucosa of influenza A and B infected individuals. The analysis included but was not limited to quantification of cytokines and chemokines detected in previous studies. SOMAscan quantified more than 1,000 secreted proteins in small nasal wash volumes from infected and healthy individuals. Our results illustrate the utility of micro-proteomic technology for analysis of proteins in small volumes of respiratory mucosal samples. Furthermore, when we compared nasal wash samples from influenza-infected patients with viral load ≥ 2⁸ and increased IL-6 and CXCL10 to healthy controls, we identified 162 differentially-expressed proteins between the two groups. This number greatly exceeds the number of DEPs identified in previous studies in human influenza patients. Most of the identified proteins were associated with the host immune response to infection, and changes in protein levels of 151 of the DEPs were significantly correlated with viral load. Most important, SOMAscan identified differentially expressed proteins heretofore not associated with respiratory influenza infection in humans. Our study is the first report for the use of SOMAscan to screen nasal secretions. It establishes a precedent for micro-proteomic quantification of proteins that reflect ongoing response to respiratory infection.

Microbiological Zoonotic Emerging Risks, Transmitted Between Livestock Animals and Humans (2007-2015)

As part of the Emerging Risk Identification (ERI) activities of the European Food Safety Authority (EFSA), a literature search was conducted to identify the microbiological agents transmitted between livestock animals and humans that have been suggested as having emerged between 2007 and 2015 in peer-reviewed scientific literature published during the same period (2007-2015). According to the criteria set, the search identified seven such zoonotic agents, namely West Nile Fever virus, Rift Valley Fever virus, Crimean-Congo Haemorrhagic Fever virus, Influenza A H1N1 virus, Coxiella burnetii, Streptococcus suis and livestock-associated methicillin-resistant Staphylococcus aureus clonal complex 398. An explanation of the agents' consideration as emerging risks is provided. The experience gained from these emergences has shown that the detection of and response to such risks can be achieved faster and more successfully within a multidisciplinary, collaborative context at the field, local, national and international levels.

Influenza H3N2 infection of the collaborative cross founder strains reveals highly divergent host responses and identifies a unique phenotype in CAST/EiJ mice

BACKGROUND

Influenza A virus is a zoonotic pathogen that poses a major threat to human and animal health. The severe course of influenza infection is not only influenced by viral virulence factors but also by individual differences in the host response. To determine the extent to which the genetic background can modulate severity of an infection, we studied the host responses to influenza infections in the eight genetically highly diverse Collaborative Cross (CC) founder mouse strains.

RESULTS

We observed highly divergent host responses between the CC founder strains with respect to survival, body weight loss, hematological parameters in the blood, relative lung weight and viral load. Mouse strain was the main factor with highest effect size on body weight loss after infection, demonstrating that this phenotype was highly heritable. Sex represented another significant main effect, although it was less strong. Analysis of survival rates and mean time to death suggested three groups of susceptibility phenotypes: highly susceptible (A/J, CAST/EiJ, WSB/EiJ), intermediate susceptible (C57BL/6J, 129S1/SvImJ, NOD/ShiLtJ) and highly resistant strains (NZO/HlLtJ, PWK/PhJ). These three susceptibility groups were significantly different with respect to death/survival counts. Viral load was significantly different between susceptible and resistant strains but not between intermediate and highly susceptible strains. CAST/EiJ mice showed a unique phenotype. Despite high viral loads in their lungs, CAST/EiJ mice exhibited low counts of infiltrating granulocytes and showed increased numbers of macrophages in the lung. Histological studies of infected lungs and transcriptome analyses of peripheral blood cells and lungs confirmed an abnormal response in the leukocyte recruitment in CAST/EiJ mice.

CONCLUSIONS

The eight CC founder strains exhibited a large diversity in their response to influenza infections. Therefore, the CC will represent an ideal mouse genetic reference population to study the influence of genetic variation on the susceptibility and resistance to influenza infections which will be important to understand individual variations of disease severity in humans. The unique phenotype combination in the CAST/EiJ strain resembles human leukocyte adhesion deficiency and may thus represent a new mouse model to understand this and related abnormal immune responses to infections in humans.

Role of Substitutions in the Hemagglutinin in the Emergence of the 1968 Pandemic Influenza Virus

Hemagglutinin (HA) of H3N2/1968 pandemic influenza viruses differs from the putative avian precursor by seven amino acid substitutions. Substitutions Q226L and G228S are known to be essential for adaptation of avian HA to mammals. We found that introduction of avian-virus-like amino acids at five other HA positions (positions 62, 81, 92, 144, and 193) of A/Hong Kong/1/1968 virus decreased viral replication in human cells and transmission in pigs. Thus, substitutions at some of these positions facilitated emergence of the pandemic virus.

Protection from Severe Influenza Virus Infections in Mice Carrying the Mx1 Influenza Virus Resistance Gene Strongly Depends on Genetic Background

Influenza virus infections represent a serious threat to human health. Both extrinsic and intrinsic factors determine the severity of influenza. The MX dynamin-like GTPase 1 (Mx1) gene has been shown to confer strong resistance to influenza A virus infections in mice. Most laboratory mouse strains, including C57BL/6J, carry nonsense or deletion mutations in Mx1 and thus a nonfunctional allele, whereas wild-derived mouse strains carry a wild-type Mx1 allele. Congenic C57BL/6J (B6-Mx1^r/r) mice expressing a wild-type allele from the A2G mouse strain are highly resistant to influenza A virus infections, to both mono- and polybasic subtypes. Furthermore, in genetic mapping studies, Mx1 was identified as the major locus of resistance to influenza virus infections. Here, we investigated whether the Mx1 protective function is influenced by the genetic background. For this, we generated a congenic mouse strain carrying the A2G wild-type Mx1 resistance allele on a DBA/2J background (D2-Mx1^r/r). Most remarkably, congenic D2-Mx1^r/r mice expressing a functional Mx1 wild-type allele are still highly susceptible to H1N1 virus. However, pretreatment of D2-Mx1^r/r mice with alpha interferon protected them from lethal infections. Our results showed, for the first time, that the presence of an Mx1 wild-type allele from A2G as such does not fully protect mice from lethal influenza A virus infections. These observations are also highly relevant for susceptibility to influenza virus infections in humans.

IMPORTANCE Influenza A virus represents a major health threat to humans. Seasonal influenza epidemics cause high economic loss, morbidity, and deaths each year. Genetic factors of the host strongly influence susceptibility and resistance to virus infections. The Mx1 (MX dynamin-like GTPase 1) gene has been described as a major resistance gene in mice and humans. Most inbred laboratory mouse strains are deficient in Mx1, but congenic B6-Mx1^r/r mice that carry the wild-type Mx1 gene from the A2G mouse strain are highly resistant. Here, we show that, very unexpectedly, congenic D2-Mx1^r/r mice carrying the wild-type Mx1 gene from the A2G strain are not fully protected against lethal influenza virus infections. These observations demonstrate that the genetic background is very important for the protective function of the Mx1 resistance gene. Our results are also highly relevant for understanding genetic susceptibility to influenza virus infections in humans.

Influenza viruses en route from birds to man

Human and other mammalian influenza viruses emerge from a large gene pool provided by avian influenza viruses. Two recent studies (Watanabe et al., 2014; Linster et al., 2014) show that adaptation to a mammalian host depends on a limited number of mutations that allow airborne transmission, a specific trait of the mammalian viruses.

Herd immunity and fatal cases of influenza among the population exposed to poultry and wild birds in Russian Asia in 2013-2014

In total 1,525 blood serum samples were collected in October, 2013 in Russian Asia from people who reside in territories that are at high risk for emergence of influenza viruses with pandemic potential. Presence of antibodies to influenza viruses in the sera was tested in hemagglutination inhibition test. None of the samples produced positive results with the antigens A/H5 and A/H7. Twelve strains of influenza A(H1N1pdm09) virus were isolated from people who died presumably from influenza during 2013-2014 epidemic season. All strains were similar to vaccine strain A/California/07/09 according to their antigenic properties and sensitivity to anti-neuraminidase drugs (oseltamivir and zanamivir). Genetic analysis revealed that all strains belong to group 6, subgroup 6B of influenza A(H1N1)pdm09 virus. Substitutions in HA1: S164F add E235K as well as E47G, A86V, K331R, N386K, N397K in NA, and K131E, N29S in NS1, and N29S, R34Q in NEP separate investigated strains into two groups: 1st group-A/Chita/1114/2014, A/Chita/1115/2014, A/Chita/853/2014, A/Barnaul/269/2014 and 2nd group-A/Chita/655/2014, A/Chita/656/2014, A/Chita/709/2014, A/Chita/873/2014. Mutation D222G in HA1, which is often associated with high morbidity of the illness, was present in strain A/Novosibirsk/114/2014. Substitution N386K in NA removes a potential N-glycosylation site in neuraminidases of A/Chita/1114/2014, A/Chita/1115/2014, A/Chita/853/2014, A/Barnaul/269/2014, A/Novosibirsk/114/2014, and A/Blagoveshensk/252/2014.

Molecular Characterisation of the Haemagglutinin Glycan-Binding Specificity of Egg-Adapted Vaccine Strains of the Pandemic 2009 H1N1 Swine Influenza A Virus

The haemagglutinin (HA) glycan binding selectivity of H1N1 influenza viruses is an important determinant for the host range of the virus and egg-adaption during vaccine production. This study integrates glycan binding data with structure-recognition models to examine the impact of the K123N, D225G and Q226R mutations (as seen in the HA of vaccine strains of the pandemic 2009 H1N1 swine influenza A virus). The glycan-binding selectivity of three A/California/07/09 vaccine production strains, and purified recombinant A/California/07/09 HAs harboring these mutations was examined via a solid-phase ELISA assay. Wild-type A/California/07/09 recombinant HA bound specifically to α2,6-linked sialyl-glycans, with no affinity for the α2,3-linked sialyl-glycans in the array. In contrast, the vaccine virus strains and recombinant HA harboring the Q226R HA mutation displayed a comparable pattern of highly specific binding to α2,3-linked sialyl-glycans, with a negligible affinity for α2,6-linked sialyl-glycans. The D225G A/California/07/09 recombinant HA displayed an enhanced binding affinity for both α2,6- and α2,3-linked sialyl-glycans in the array. Notably its α2,6-glycan affinity was generally higher compared to its α2,3-glycan affinity, which may explain why the double mutant was not naturally selected during egg-adaption of the virus. The K123N mutation which introduces a glycosylation site proximal to the receptor binding site, did not impact the α2,3/α2,6 glycan selectivity, however, it lowered the overall glycan binding affinity of the HA; suggesting glycosylation may interfere with receptor binding. Docking models and 'per residues' scoring were employed to provide a structure-recognition rational for the experimental glycan binding data. Collectively, the glycan binding data inform future vaccine design strategies to introduce the D225G or Q226R amino acid substitutions into recombinant H1N1 viruses.

The avian-origin PB1 gene segment facilitated replication and transmissibility of the H3N2/1968 pandemic influenza virus

The H2N2/1957 and H3N2/1968 pandemic influenza viruses emerged via the exchange of genomic RNA segments between human and avian viruses. The avian hemagglutinin (HA) allowed the hybrid viruses to escape preexisting immunity in the human population. Both pandemic viruses further received the PB1 gene segment from the avian parent (Y. Kawaoka, S. Krauss, and R. G. Webster, J Virol 63:4603-4608, 1989), but the biological significance of this observation was not understood. To assess whether the avian-origin PB1 segment provided pandemic viruses with some selective advantage, either on its own or via cooperation with the homologous HA segment, we modeled by reverse genetics the reassortment event that led to the emergence of the H3N2/1968 pandemic virus. Using seasonal H2N2 virus A/California/1/66 (Cal) as a surrogate precursor human virus and pandemic virus A/Hong Kong/1/68 (H3N2) (HK) as a source of avian-derived PB1 and HA gene segments, we generated four reassortant recombinant viruses and compared pairs of viruses which differed solely by the origin of PB1. Replacement of the PB1 segment of Cal by PB1 of HK facilitated viral polymerase activity, replication efficiency in human cells, and contact transmission in guinea pigs. A combination of PB1 and HA segments of HK did not enhance replicative fitness of the reassortant virus compared with the single-gene PB1 reassortant. Our data suggest that the avian PB1 segment of the 1968 pandemic virus served to enhance viral growth and transmissibility, likely by enhancing activity of the viral polymerase complex.

IMPORTANCE

Despite the high impact of influenza pandemics on human health, some mechanisms underlying the emergence of pandemic influenza viruses still are poorly understood. Thus, it was unclear why both H2N2/1957 and H3N2/1968 reassortant pandemic viruses contained, in addition to the avian HA, the PB1 gene segment of the avian parent. Here, we addressed this long-standing question by modeling the emergence of the H3N2/1968 virus from its putative human and avian precursors. We show that the avian PB1 segment increased activity of the viral polymerase and facilitated viral replication. Our results suggest that in addition to the acquisition of antigenically novel HA (i.e., antigenic shift), enhanced viral polymerase activity is required for the emergence of pandemic influenza viruses from their seasonal human precursors.

The interferon-induced gene Ifi27l2a is active in lung macrophages and lymphocytes after influenza A infection but deletion of Ifi27l2a in mice does not increase susceptibility to infection

Interferons represent one of the first and essential host defense mechanisms after infection, and the activation of the IFN-pathway results in the transcriptional activation of hundreds of interferon-stimulated genes. The alpha-inducible protein 27 like 2A (Ifi27l2a) gene (human synonym: ISG12) is strongly up-regulated in the lung after influenza A infection in mice and has been shown in gene expression studies to be highly correlated to other activated genes. Therefore, we investigated the role of Ifi27l2a for the host defense to influenza A infections in more detail. RT-PCR analyses in non-infected mice demonstrated that Ifi27l2a was expressed in several tissues, including the lung. Detailed analyses of reporter gene expression in lungs from Ifi27l2a-LacZ mice revealed that Ifi27l2a was expressed in macrophages and lymphocytes but not in alveolar cells or bronchiolar epithelium cells. The number of macrophages and lymphocyte strongly increased in the lung after infection, but no significant increase in expression levels of the LacZ reporter gene was found within individual immune cells. Also, no reporter gene expression was found in bronchiolar epithelial cells, alveolar cells or infiltrating neutrophils after infection. Thus, up-regulation of Ifi27l2a in infected lungs is mainly due to the infiltration of macrophages and lymphocytes. Most surprisingly, deletion of Ifi27l2a in mouse knock-out lines did not result in increased susceptibility to infections with H1N1 or H7N7 influenza A virus compared to wild type C57BL/6N mice, suggesting a less important role of the gene for the host response to influenza infections than for bacterial infections.

Protective efficacy of passive immunization with monoclonal antibodies in animal models of H5N1 highly pathogenic avian influenza virus infection

Highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype often cause severe pneumonia and multiple organ failure in humans, with reported case fatality rates of more than 60%. To develop a clinical antibody therapy, we generated a human-mouse chimeric monoclonal antibody (MAb) ch61 that showed strong neutralizing activity against H5N1 HPAI viruses isolated from humans and evaluated its protective potential in mouse and nonhuman primate models of H5N1 HPAI virus infections. Passive immunization with MAb ch61 one day before or after challenge with a lethal dose of the virus completely protected mice, and partial protection was achieved when mice were treated 3 days after the challenge. In a cynomolgus macaque model, reduced viral loads and partial protection against lethal infection were observed in macaques treated with MAb ch61 intravenously one and three days after challenge. Protective effects were also noted in macaques under immunosuppression. Though mutant viruses escaping from neutralization by MAb ch61 were recovered from macaques treated with this MAb alone, combined treatment with MAb ch61 and peramivir reduced the emergence of escape mutants. Our results indicate that antibody therapy might be beneficial in reducing viral loads and delaying disease progression during H5N1 HPAI virus infection in clinical cases and combined treatment with other antiviral compounds should improve the protective effects of antibody therapy against H5N1 HPAI virus infection.

The H5N1 highly pathogenic avian influenza virus has been circulating in poultry in Asia, the Middle East, and Africa since its first appearance in southern China in 1996. This virus occasionally infects humans with a high case mortality rate and poses a significant pandemic threat. Since neutralizing antibodies generally play a major role in protective immunity against influenza viruses, antibody therapy is a potential option for preventing highly lethal infection with the H5N1 virus in humans. Here we evaluated the protective potential of a human-mouse chimeric monoclonal antibody with strong neutralizing activity against H5N1 viruses in mouse and nonhuman primate models of lethal H5N1 virus infection. The therapeutic use of the neutralizing antibody resulted in reduced viral loads and improved survival in animals infected with highly pathogenic H5N1 viruses. It was noted that the protective effects were more prominent in immunosuppressed macaques, which might provide a model of protection against severe clinical disease in immunocompromised patients. In addition, combination therapy together with an antiviral drug reduced the selection of escape mutants. Collectively, this study suggests that antibody therapy may have beneficial effects in clinical cases of H5N1 HPAI virus infection in humans.

The zoonotic potential of avian influenza viruses isolated from wild waterfowl in Zambia

Whilst remarkable progress in elucidating the mechanisms governing interspecies transmission and pathogenicity of highly pathogenic avian influenza viruses (AIVs) has been made, similar studies focusing on low-pathogenic AIVs isolated from the wild waterfowl reservoir are limited. We previously reported that two AIV strains (subtypes H6N2 and H3N8) isolated from wild waterfowl in Zambia harbored some amino acid residues preferentially associated with human influenza virus proteins (so-called human signatures) and replicated better in the lungs of infected mice and caused more morbidity than a strain lacking such residues. To further substantiate these observations, we infected chickens and mice intranasally with AIV strains of various subtypes (H3N6, H3N8, H4N6, H6N2, H9N1 and H11N9) isolated from wild waterfowl in Zambia. Although some strains induced seroconversion, all of the tested strains replicated poorly and were nonpathogenic for chickens. In contrast, most of the strains having human signatures replicated well in the lungs of mice, and one of these strains caused severe illness in mice and induced lung injury that was characterized by a severe accumulation of polymorphonuclear leukocytes. These results suggest that some strains tested in this study may have the potential to infect mammalian hosts directly without adaptation, which might possibly be associated with the possession of human signature residues. Close monitoring and evaluation of host-associated signatures may help to elucidate the prevalence and emergence of AIVs with potential for causing zoonotic infections.

Importin-α7 is required for enhanced influenza A virus replication in the alveolar epithelium and severe lung damage in mice

Influenza A viruses recruit components of the nuclear import pathway to enter the host cell nucleus and promote viral replication. Here, we analyzed the role of the nuclear import factor importin-α7 in H1N1 influenza virus pulmonary tropism by using various ex vivo imaging techniques (magnetic resonance imaging, confocal laser scanning microscopy, and correlative light-electron microscopy). We infected importin-α7 gene-deficient (α7(-/-)) mice with a recombinant H1N1 influenza virus and compared the in vivo viral kinetics with those in wild-type (WT) mice. In WT mice, influenza virus replication in the bronchial and alveolar epithelium already occurred a few days after infection. Accordingly, extensive mononuclear infiltration and alveolar destruction were present in the lungs of infected WT mice, followed by 100% lethality. Conversely, in α7(-/-) mice, virus replication was restricted mostly to the bronchial epithelium with marginal alveolar infection, resulting in significantly reduced lung damage and enhanced animal survival. To investigate the host immune response during alveolar virus replication, we studied the role of primary macrophages in virus propagation and clearance. The ability of macrophages to support or clear the virus infection, as well as the host cellular immune responses, did not significantly differ between WT and α7(-/-) mice. However, cytokine and chemokine responses were generally elevated in WT mice, likely reflective of increased viral replication in the lung. In summary, these data show that a cellular factor, importin-α7, is required for enhanced virus replication in the alveolar epithelium, resulting in elevated cytokine and chemokine levels, extensive mononuclear infiltration, and thus, severe pneumonia and enhanced virulence in mice. Importance: Influenza A viruses are respiratory pathogens that may cause pneumonia in humans. Viral infection and replication in the alveoli of the respiratory tract are believed to be crucial for the development of the acute respiratory distress syndrome associated with fatal outcomes in influenza virus-infected patients. Here, we report the requirement of a cellular factor, importin-α7, for efficient virus replication in the alveolar epithelium of mice. Using complementary ex vivo imaging approaches, we show that influenza virus replication is restricted to the bronchial epithelium, followed by enhanced survival in importin-α7-deficient mice. In contrast, the presence of this gene results in enhanced virus replication in the alveoli, elevated cytokine and chemokine responses, mononuclear infiltration, alveolar destruction, and 100% lethality in wild-type mice. Taken together, our results show that importin-α7 is particularly required for virus replication in the alveolar epithelium in association with severe pneumonia and death in mice.

Effects of a hemagglutinin D222G substitution on the pathogenicity of 2009 influenza A (H1N1) virus in mice

The surface glycoprotein hemagglutinin (HA) of influenza virus initiates the infection process by binding to sialic acid receptors on upper respiratory cells in the host. In contrast to avian influenza viruses, which bind to sialic acids connected by an α2-3 linkage to the penultimate galactose, human influenza viruses prefer sialic acids with an α2-6 linkage. Recently, there have been multiple cases of severe human infections associated with an HA D222G mutant influenza virus. In this study, we have investigated the pathogenic effects of the HA D222G substitution in a 2009 pandemic H1N1 virus in mice. Compared with the A/Korea/01/2009 (K/09) virus, the HA D222G mutant showed reduced growth in cells and reduced binding avidity to human and turkey red blood cells. In a BALB/c mouse infection model, infection with the HA D222G mutant virus resulted in less body weight loss when compared to the parental K/09 virus. Altogether, our data suggest that the HA D222G substitution in the K/09 virus might be deleterious to viral fitness.

Virus-specific factors associated with zoonotic and pandemic potential

Influenza A is a highly contagious respiratory virus in constant evolution and represents a threat to both veterinary and human public health. IA viruses (IAVs) originate in avian reservoirs but may adapt to humans, either directly or through the spillover to another mammalian species, to the point of becoming pandemic. IAVs must successfully be able to (i) transmit from animal to human, (ii) interact with host cells, and (iii) transmit from human to human. The mechanisms by which viruses evolve, cause zoonotic infections, and adapt to a new host species are indeed complex and appear to be a heterogeneous collection of viral evolutionary events rather than a single phenomenon. Progress has been made in identifying some of the genetic markers mainly associated with virulence and transmission; this achievement has improved our knowledge of how to manage a pandemic event and of how to identify IAVs with pandemic potential. Early evidence of emerging viruses and surveillance of animal IAVs is made possible only by strengthening the collaboration between the public and veterinary health sectors.

A new class of synthetic anti-lipopolysaccharide peptides inhibits influenza A virus replication by blocking cellular attachment

Influenza A viruses are a continuous threat to human health as illustrated by the 2009 H1N1 pandemic. Since circulating influenza virus strains become increasingly resistant against currently available drugs, the development of novel antivirals is urgently needed. Here, we have evaluated a recently described new class of broad-spectrum antiviral peptides (synthetic anti-lipopolysaccharide peptides; SALPs) for their potential to inhibit influenza virus replication in vitro and in vivo. We found that particularly SALP PEP 19-2.5 shows high binding affinities for the influenza virus receptor molecule, N-Acetylneuraminic acid, leading to impaired viral attachment and cellular entry. As a result, replication of several influenza virus subtypes (H7N7, H3N2 and 2009 pandemic H1N1) was strongly reduced. Furthermore, mice co-treated with PEP 19-2.5 were protected against an otherwise 100% lethal H7N7 influenza virus infection. These findings show that SALPs exhibit antiviral activity against influenza viruses by blocking virus attachment and entry into host cells. Thus, SALPs present a new class of broad-spectrum antiviral peptides for further development for influenza virus therapy.

Modeling the association of space, time, and host species with variation of the HA, NA, and NS genes of H5N1 highly pathogenic avian influenza viruses isolated from birds in Romania in 2005-2007

Molecular characterization studies of a diverse collection of avian influenza viruses (AIVs) have demonstrated that AIVs' greatest genetic variability lies in the HA, NA, and NS genes. The objective here was to quantify the association between geographical locations, periods of time, and host species and pairwise nucleotide variation in the HA, NA, and NS genes of 70 isolates of H5N1 highly pathogenic avian influenza virus (HPAIV) collected from October 2005 to December 2007 from birds in Romania. A mixed-binomial Bayesian regression model was used to quantify the probability of nucleotide variation between isolates and its association with space, time, and host species. As expected for the three target genes, a higher probability of nucleotide differences (odds ratios [ORs] > 1) was found between viruses sampled from places at greater geographical distances from each other, viruses sampled over greater periods of time, and viruses derived from different species. The modeling approach in the present study maybe useful in further understanding the molecular epidemiology of H5N1 HPAI virus in bird populations. The methodology presented here will be useful in predicting the most likely genetic distance for any of the three gene segments of viruses that have not yet been isolated or sequenced based on space, time, and host species during the course of an epidemic.

Protease activation mutants elicit protective immunity against highly pathogenic avian influenza viruses of subtype H7 in chickens and mice

Protease activation mutants of the highly pathogenic avian influenza virus A/FPV/Rostock/34 (H7N1) have been generated that are fully dependent on the presence of trypsin for growth in cell culture. Unlike wild-type virus, the mutants do not induce systemic infection in chicken embryos and show low pathogenicity in both chicken embryos and adult chickens. Inactivated vaccines prepared from the mutants protected chickens and mice very efficiently against infection with highly pathogenic wild-type virus in a cross-reactive manner. The potential of these mutants to be used as veterinary and prepandemic vaccines will be discussed.

Acquisition of a novel eleven amino acid insertion directly N-terminal to a tetrabasic cleavage site confers intracellular cleavage of an H7N7 influenza virus hemagglutinin

A critical feature of highly pathogenic avian influenza viruses (H5N1 and H7N7) is the efficient intracellular cleavage of the hemagglutinin (HA) protein. H7N7 viruses also exist in equine species, and a unique feature of the equine H7N7 HA is the presence of an eleven amino acid insertion directly N-terminal to a tetrabasic cleavage site. Here, we show that three histidine residues within the unique insertion of the equine H7N7 HA are essential for intracellular cleavage. An asparagine residue within the insertion-derived glycosylation site was also found to be essential for intracellular cleavage. The presence of the histidine residues also appear to be involved in triggering fusion, since mutation of the histidine residues resulted in a destabilizing effect. Importantly, the addition of a tetrabasic site and the eleven amino acid insertion conferred efficient intracellular cleavage to the HA of an H7N3 low pathogenicity avian influenza virus. Our studies show that acquisition of the eleven amino acid insertion offers an alternative mechanism for intracellular cleavage of influenza HA.

Immunization with live virus vaccine protects highly susceptible DBA/2J mice from lethal influenza A H1N1 infection

BACKGROUND

The mouse represents an important model system to study the host response to influenza A infections and to evaluate new prevention or treatment strategies. We and others reported that the susceptibility to influenza A virus infections strongly varies among different inbred mouse strains. In particular, DBA/2J mice are highly susceptible to several influenza A subtypes, including human isolates and exhibit severe symptoms after infection with clinical isolates.

FINDINGS

Upon intra-muscular immunization with live H1N1 influenza A virus (mouse-adapted PR8M, and 2009 pandemic human HA04), DBA/2J mice mounted virus-specific IgG responses and were protected against a subsequent lethal challenge. The immune response and rescue from death after immunization in DBA/2J was similar to those observed for C57BL/6J mice.

CONCLUSIONS

DBA/2J mice represent a suitable mouse model to evaluate virulence and pathogenicity as well as immunization regimes against existing and newly emerging human influenza strains without the need for prior adaptation of the virus to the mouse.

The Mouse as Model System to Study Host-Pathogen Interactions in Influenza A Infections

The mouse is one of the most important mammalian model systems for studying host-pathogen-interactions during influenza A virus infections and for assessing the virulence of newly emerging influenza viruses. Here, we provide the basic protocols for infecting mice with influenza virus and studying the main pathological changes associated with disease. Critical parameters, e.g., virus variants and subtypes or mouse strains, are discussed. Curr. Protoc. Mouse Biol. 2:177-205 © 2012 by John Wiley & Sons, Inc.

Influenza-related pneumonia

Influenza-related pneumonia encompasses both primary viral pneumonia and secondary bacterial pneumonia, which may be difficult to differentiate clinically. A high index of suspicion, prompt initiation of antiviral and antibiotic therapy, and appropriate escalation to secondary/critical care are key to improving outcome.

Validation of the gravity model in predicting the global spread of influenza

The gravity model is often used in predicting the spread of influenza. We use the data of influenza A (H1N1) to check the model's performance and validation, in order to determine the scope of its application. In this article, we proposed to model the pattern of global spread of the virus via a few important socio-economic indicators. We applied the epidemic gravity model for modelling the virus spread globally through the estimation of parameters of a generalized linear model. We compiled the daily confirmed cases of influenza A (H1N1) in each country as reported to the WHO and each state in the USA, and established the model to describe the relationship between the confirmed cases and socio-economic factors such as population size, per capita gross domestic production (GDP), and the distance between the countries/states and the country where the first confirmed case was reported (i.e., Mexico). The covariates we selected for the model were all statistically significantly associated with the global spread of influenza A (H1N1). However, within the USA, the distance and GDP were not significantly associated with the number of confirmed cases. The combination of the gravity model and generalized linear model provided a quick assessment of pandemic spread globally. The gravity model is valid if the spread period is long enough for estimating the model parameters. Meanwhile, the distance between donor and recipient communities has a good gradient. Besides, the spread should be at the early stage if a single source is taking into account.