A(H7N9) virus results in early induction of proinflammatory cytokine responses in both human lung epithelial and endothelial cells and shows increased human adaptation compared with avian H5N1 virus

Statins for the prevention of cardiovascular events associated with avian influenza: the COVID-19 pandemic as a reference

There is growing concern that the severe respiratory disease in birds (avian influenza or 'bird flu') caused by the H5N1 influenza virus, might potentially spread more widely to humans and cause a pandemic. Here we discuss clinical issues related to human infections by the highly pathogenic H5N1 subtype of the avian influenza A virus and make a clinical comparison with recent information obtained from studies of SARS-CoV-2 infection. Firstly, we consider the potential increase in cardiovascular events in humans infected with the H5N1 virus. Like SARS-CoV-2 infection, H5N1 infection may result in endothelial dysfunction and the associated procoagulant and prothrombotic state, and via this mechanism, the infection can potentially increase cardiovascular morbidity, especially in vulnerable individuals with pre-existing cardiovascular disease. Secondly, we discuss the potential beneficial role of statin use, both in the prophylaxis and the treatment of individuals with influenza A(H5N1), as was found favorable for the treatment of COVID-19 caused by SARS-CoV-2 infection.

Hussein S, Abdalhabib EK, Nabi SU. The critical impacts of cytokine storms in respiratory disorders

Cytokine storm (CS) refers to the spontaneous dysregulated and hyper-activated inflammatory reaction occurring in various clinical conditions, ranging from microbial infection to end-stage organ failure. Recently the novel coronavirus involved in COVID-19 (Coronavirus disease-19) caused by SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) has been associated with the pathological phenomenon of CS in critically ill patients. Furthermore, critically ill patients suffering from CS are likely to have a grave prognosis and a higher case fatality rate. Pathologically CS is manifested as hyper-immune activation and is clinically manifested as multiple organ failure. An in-depth understanding of the etiology of CS will enable the discovery of not just disease risk factors of CS but also therapeutic approaches to modulate the immune response and improve outcomes in patients with respiratory diseases having CS in the pathogenic pathway. Owing to the grave consequences of CS in various diseases, this phenomenon has attracted the attention of researchers and clinicians throughout the globe. So in the present manuscript, we have attempted to discuss CS and its ramifications in COVID-19 and other respiratory diseases, as well as prospective treatment approaches and biomarkers of the cytokine storm. Furthermore, we have attempted to provide in-depth insight into CS from both a prophylactic and therapeutic point of view. In addition, we have included recent findings of CS in respiratory diseases reported from different parts of the world, which are based on expert opinion, clinical case-control research, experimental research, and a case-controlled cohort approach.

Probenecid Inhibits Influenza A(H5N1) and A(H7N9) Viruses In Vitro and in Mice

Avian influenza (AI) viruses cause infection in birds and humans. Several H5N1 and H7N9 variants are highly pathogenic avian influenza (HPAI) viruses. H5N1 is a highly infectious bird virus infecting primarily poultry, but unlike other AIs, H5N1 also infects mammals and transmits to humans with a case fatality rate above 40%. Similarly, H7N9 can infect humans, with a case fatality rate of over 40%. Since 1996, there have been several HPAI outbreaks affecting humans, emphasizing the need for safe and effective antivirals. We show that probenecid potently inhibits H5N1 and H7N9 replication in prophylactically or therapeutically treated A549 cells and normal human broncho-epithelial (NHBE) cells, and H5N1 replication in VeroE6 cells and mice.

The Potential Role of Cytokine Storm Pathway in the Clinical Course of Viral Respiratory Pandemic

The "cytokine storm" (CS) consists of a spectrum of different immune dysregulation disorders characterized by constitutional symptoms, systemic inflammation and multiorgan dysfunction triggered by an uncontrolled immune response. Particularly in respiratory virus infections, the cytokine storm plays a primary role in the pathogenesis of respiratory disease and the clinical outcome of respiratory diseases, leading to complications such as alveolar edema and hypoxia. In this review, we wanted to analyze the different pathogenetic mechanisms involved in the various respiratory viral pandemics (COVID-19; SARS; MERS; H1N1 influenza A and Spanish flu) which have affected humans in this and last century, with particular attention to the phenomenon of the "cytokine storm" which determines the clinical severity of the respiratory disease and consequently its lethality.

Drug repositioning of Clopidogrel or Triamterene to inhibit influenza virus replication in vitro

Influenza viruses cause respiratory tract infections and substantial health concerns. Infection may result in mild to severe respiratory disease associated with morbidity and some mortality. Several anti-influenza drugs are available, but these agents target viral components and are susceptible to drug resistance. There is a need for new antiviral drug strategies that include repurposing of clinically approved drugs. Drugs that target cellular machinery necessary for influenza virus replication can provide a means for inhibiting influenza virus replication. We used RNA interference screening to identify key host cell genes required for influenza replication, and then FDA-approved drugs that could be repurposed for targeting host genes. We examined the effects of Clopidogrel and Triamterene to inhibit A/WSN/33 (EC50 5.84 uM and 31.48 uM, respectively), A/CA/04/09 (EC50 6.432 uM and 3.32 uM, respectively), and B/Yamagata/16/1988 (EC50 0.28 uM and 0.11 uM, respectively) replication. Clopidogrel and Triamterene provide a druggable approach to influenza treatment across multiple strains and subtypes.

H7N9 Influenza Virus in China

In early 2013, human infections caused by a novel H7N9 avian influenza virus (AIV) were first reported in China; these infections caused severe disease and death. The virus was initially low pathogenic to poultry, enabling it to spread widely in different provinces, especially in live poultry markets. Importantly, the H7N9 low pathogenic AIVs (LPAIVs) evolved into highly pathogenic AIVs (HPAIVs) in the beginning of 2017, causing a greater threat to human health and devastating losses to the poultry industry. Fortunately, nationwide vaccination of chickens with an H5/H7 bivalent inactivated avian influenza vaccine since September 2017 has successfully controlled H7N9 avian influenza infections in poultry and, importantly, has also prevented human infections. In this review, we summarize the biological properties of the H7N9 viruses, specifically their genetic evolution, adaptation, pathogenesis, receptor binding, transmission, drug resistance, and antigenic variation, as well as the prevention and control measures. The information obtained from investigating and managing the H7N9 viruses could improve our ability to understand other novel AIVs and formulate effective measures to control their threat to humans and animals.

Cytokine/Chemokine Expression Is Closely Associated Disease Severity of Human Adenovirus Infections in Immunocompetent Adults and Predicts Disease Progression

Increasing human Adenovirus (HAdV) infections complicated with acute respiratory distress syndrome (ARDS) even fatal outcome were reported in immunocompetent adolescent and adult patients. Here, we characterized the cytokine/chemokine expression profiles of immunocompetent patients complicated with ARDS during HAdV infection and identified biomarkers for disease severity/progression. Forty-eight cytokines/chemokines in the plasma samples from 19 HAdV-infected immunocompetent adolescent and adult patients (ten complicated with ARDS) were measured and analyzed in combination with clinical indices. Immunocompetent patients with ARDS caused by severe acute respiratory disease coronavirus (SARS-CoV)-2, 2009 pandemic H1N1 (panH1N1) or bacteria were included for comparative analyses. Similar indices of disease course/progression were found in immunocompetent patients with ARDS caused by HAdV, SARS-CoV-2 or panH1N infections, whereas the HAdV-infected group showed a higher prevalence of viremia, as well as increased levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and creatine kinase (CK). Expression levels of 33 cytokines/chemokines were increased significantly in HAdV-infected patients with ARDS compared with that in healthy controls, and many of them were also significantly higher than those in SARS-CoV-2-infected and panH1N1-infected patients. Expression of interferon (IFN)-γ, interleukin (IL)-1β, hepatocyte growth factor (HGF), monokine induced by IFN-γ (MIG), IL-6, macrophage-colony stimulating factor (M-CSF), IL-10, IL-1α and IL-2Ra was significantly higher in HAdV-infected patients with ARDS than that in those without ARDS, and negatively associated with the ratio of the partial pressure of oxygen in arterial blood/fraction of inspired oxygen (PaO₂/FiO₂). Analyses of the receiver operating characteristic curve (ROC) showed that expression of IL-10, M-CSF, MIG, HGF, IL-1β, IFN-γ and IL-2Ra could predict the progression of HAdV infection, with the highest area under the curve (AUC) of 0.944 obtained for IL-10. Of note, the AUC value for the combination of IL-10, IFN-γ, and M-CSF reached 1. In conclusion, the “cytokine storm” occurred during HAdV infection in immunocompetent patients, and expression of IL-10, M-CSF, MIG, HGF, IL-1β, IFN-γ and IL-2Ra was closely associated with disease severity and could predict disease progression.

SARS-CoV-2 Causes a Different Cytokine Response Compared to Other Cytokine Storm-Causing Respiratory Viruses in Severely Ill Patients

Hyper-induction of pro-inflammatory cytokines, also known as a cytokine storm or cytokine release syndrome (CRS), is one of the key aspects of the currently ongoing SARS-CoV-2 pandemic. This process occurs when a large number of innate and adaptive immune cells activate and start producing pro-inflammatory cytokines, establishing an exacerbated feedback loop of inflammation. It is one of the factors contributing to the mortality observed with coronavirus 2019 (COVID-19) for a subgroup of patients. CRS is not unique to the SARS-CoV-2 infection; it was prevalent in most of the major human coronavirus and influenza A subtype outbreaks of the past two decades (H5N1, SARS-CoV, MERS-CoV, and H7N9). With a comprehensive literature search, we collected changing the cytokine levels from patients upon infection with the viral pathogens mentioned above. We analyzed published patient data to highlight the conserved and unique cytokine responses caused by these viruses. Our curation indicates that the cytokine response induced by SARS-CoV-2 is different compared to other CRS-causing respiratory viruses, as SARS-CoV-2 does not always induce specific cytokines like other coronaviruses or influenza do, such as IL-2, IL-10, IL-4, or IL-5. Comparing the collated cytokine responses caused by the analyzed viruses highlights a SARS-CoV-2-specific dysregulation of the type-I interferon (IFN) response and its downstream cytokine signatures. The map of responses gathered in this study could help specialists identify interventions that alleviate CRS in different diseases and evaluate whether they could be used in the COVID-19 cases.

Role of the Host Genetic Susceptibility to 2009 Pandemic Influenza A H1N1

Influenza A virus (IAV) is the most common infectious agent in humans, and infects approximately 10-20% of the world's population, resulting in 3-5 million hospitalizations per year. A scientific literature search was performed using the PubMed database and the Medical Subject Headings (MeSH) "Influenza A H1N1" and "Genetic susceptibility". Due to the amount of information and evidence about genetic susceptibility generated from the studies carried out in the last influenza A H1N1 pandemic, studies published between January 2009 to May 2020 were considered; 119 papers were found. Several pathways are involved in the host defense against IAV infection (innate immune response, pro-inflammatory cytokines, chemokines, complement activation, and HLA molecules participating in viral antigen presentation). On the other hand, single nucleotide polymorphisms (SNPs) are a type of variation involving the change of a single base pair that can mean that encoded proteins do not carry out their functions properly, allowing higher viral replication and abnormal host response to infection, such as a cytokine storm. Some of the most studied SNPs associated with IAV infection genetic susceptibility are located in the FCGR2A, C1QBP, CD55, and RPAIN genes, affecting host immune responses through abnormal complement activation. Also, SNPs in IFITM3 (which participates in endosomes and lysosomes fusion) represent some of the most critical polymorphisms associated with IAV infection, suggesting an ineffective virus clearance. Regarding inflammatory response genes, single nucleotide variants in IL1B, TNF, LTA IL17A, IL8, IL6, IRAK2, PIK3CG, and HLA complex are associated with altered phenotype in pro-inflammatory molecules, participating in IAV infection and the severest form of the disease.

Genetically and Antigenically Divergent Influenza A(H9N2) Viruses Exhibit Differential Replication and Transmission Phenotypes in Mammalian Models

Low-pathogenicity avian influenza A(H9N2) viruses, enzootic in poultry populations in Asia, are associated with fewer confirmed human infections but higher rates of seropositivity compared to A(H5) or A(H7) subtype viruses. Cocirculation of A(H5) and A(H7) viruses leads to the generation of reassortant viruses bearing A(H9N2) internal genes with markers of mammalian adaptation, warranting continued surveillance in both avian and human populations. Here, we describe active surveillance efforts in live poultry markets in Vietnam in 2018 and compare representative viruses to G1 and Y280 lineage viruses that have infected humans. Receptor binding properties, pH thresholds for HA activation, in vitro replication in human respiratory tract cells, and in vivo mammalian pathogenicity and transmissibility were investigated. While A(H9N2) viruses from both poultry and humans exhibited features associated with mammalian adaptation, one human isolate from 2018, A/Anhui-Lujiang/39/2018, exhibited increased capacity for replication and transmission, demonstrating the pandemic potential of A(H9N2) viruses.IMPORTANCE A(H9N2) influenza viruses are widespread in poultry in many parts of the world and for over 20 years have sporadically jumped species barriers to cause human infection. As these viruses continue to diversify genetically and antigenically, it is critical to closely monitor viruses responsible for human infections, to ascertain if A(H9N2) viruses are acquiring properties that make them better suited to infect and spread among humans. In this study, we describe an active poultry surveillance system established in Vietnam to identify the scope of influenza viruses present in live bird markets and the threat they pose to human health. Assessment of a recent A(H9N2) virus isolated from an individual in China in 2018 is also reported, and it was found to exhibit properties of adaptation to humans and, importantly, it shows similarities to strains isolated from the live bird markets of Vietnam.

Pulmonary endothelium-derived PD-L1 induced by the H9N2 avian influenza virus inhibits the immune response of T cells

BACKGROUND

The PD-1/PD-L1 pathway is an inhibitory signaling pathway that maintains the balance between the immune response and immunotolerance, and its overactivation in cancer and viral infections inhibits T cell function. The target cells of various viruses, microvascular endothelial cells (MECs) have been shown to be key regulatory points in immune regulation and virion diffusion in vivo during infection with multiple influenza virus subtypes. Furthermore, avian influenza virus (AIV) infection can induce immunosuppression by causing imbalances in immune responses and immune organ damage. Thus, the aim of this study was to investigate whether the H9N2 virus inhibited the immune function of T cells that migrated across MECs by upregulating PD-L1 expression on MECs.

METHODS

The susceptibility of rat pulmonary microvascular endothelial cells (RPMECs) to the H9N2 virus was evaluated by a plaque-forming assay and immunofluorescence staining. Then, we quantified the mRNA and protein levels of PD-L1 in RPMECs induced by H9N2 virus infection using quantitative real-time PCR and flow cytometry. The interaction between the activated T cells and RPMECs infected with the H9N2 virus was revealed using a coculture system. The effect of endothelial-derived PD-L1 on T cell function was investigated by using ELISA and flow cytometry with or without a PD-L1-specific antibody.

RESULTS

Surface staining and the plaque-forming assay showed that the H9N2 virus infected and replicated in RPMECs. Both the PD-L1 mRNA level and PD-L1 protein level were upregulated in RPMECs infected with the H9N2 virus. H9N2 virus-induced PD-L1 expression significantly reduced the secretions of IL-2, IFN-γ and granzyme B and perforin expression in T cells. The above data were significantly increased after treatment with an anti-PD-L1 antibody, confirming the above mentioned findings. In addition, the induction of PD-L1 expression decreased the proliferative capacity of the cocultured T cells but did not affect the apoptosis rate of T cells.

CONCLUSIONS

Taken together, the results suggest that the H9N2 virus is able to inhibit the T cell immune response by upregulating PD-L1 expression in pulmonary microvascular endothelial cells.

Plasma IP-10 and MCP-3 levels are highly associated with disease severity and predict the progression of COVID-19

BACKGROUND

The outbreak of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 was first reported in Wuhan, December 2019, and continuously poses a serious threat to public health, highlighting the urgent need of identifying biomarkers for disease severity and progression.

OBJECTIVE

We sought to identify biomarkers for disease severity and progression of COVID-19.

METHODS

Forty-eight cytokines in the plasma samples from 50 COVID-19 cases including 11 critically ill, 25 severe, and 14 moderate patients were measured and analyzed in combination with clinical data.

RESULTS

Levels of 14 cytokines were found to be significantly elevated in COVID-19 cases and showed different expression profiles in patients with different disease severity. Moreover, expression levels of IFN-γ-induced protein 10, monocyte chemotactic protein-3, hepatocyte growth factor, monokine-induced gamma IFN, and macrophage inflammatory protein 1 alpha, which were shown to be highly associated with disease severity during disease progression, were remarkably higher in critically ill patients, followed by severe and then the moderate patients. Serial detection of the 5 cytokines in 16 cases showed that continuously high levels were associated with deteriorated progression of disease and fatal outcome. Furthermore, IFN-γ-induced protein 10 and monocyte chemotactic protein-3 were excellent predictors for the progression of COVID-19, and the combination of the 2 cytokines showed the biggest area under the curve of the receiver-operating characteristics calculations with a value of 0.99.

CONCLUSIONS

In this study, we report biomarkers that are highly associated with disease severity and progression of COVID-19. These findings add to our understanding of the immunopathologic mechanisms of severe acute respiratory syndrome coronavirus 2 infection, and provide potential therapeutic targets and strategies.

Cytokine Profile in Human Peripheral Blood Mononuclear Leukocytes Exposed to Immunoadjuvant and Adjuvant-Free Vaccines Against Influenza

Background: In the last decade, adjuvant-containing vaccines, exerting different effects on the immune system, including the production of cytokines, which are one of the most important regulatory systems of the body, are introduced into practice. Objectives: An effect of the immunoadjuvant polymer-subunit and adjuvant-free vaccines against influenza on the cytokine profile of mononuclear leukocytes in 27 healthy women was studied. Methods: The study of cytokine profile in human peripheral blood mononuclear leukocytes exposed to vaccines against influenza virus was determined by flow cytometry method (Cytomix FC-500, Beckman Coulter, USA) using the Multiplex-13 test system (Bender MedSystems, Austria). Results: It was established that all the studied vaccines leaded to somewhat increased levels of Th1/Th2/Th17/Th9/Th22 cytokines in the culture fluid of peripheral blood mononuclear leukocytes (PBML), which indicates the activation of both humoral and cellular immunity. An immunoadjuvant vaccine has been shown to be superior in activating the synthesis of Th1 (IL-12, INF-g, IL-2, IL-6, IL-1β, TNF-α) cytokines, IL-9 and IL-22, while the subunit vaccine was superior in activating the synthesis of IL-4, and split vaccine-of IL-5. Conclusions: Immunoadjuvant vaccine is superior in terms of inducing cellular immune effectors to a greater extent compared to subunit and split vaccines.

Clinical and Immunological Characteristics of Human Infections With H5N6 Avian Influenza Virus

BACKGROUND

H5N6 avian influenza virus (AIV) has caused sporadic, recurring outbreaks in China and Southeast Asia since 2013, with 19 human infections and 13 deaths. Seventeen of these infections occurred since December 2015, indicating a recent rise in the frequency of H5N6 cases.

METHODS

To assess the relative threat of H5N6 virus to humans, we summarized and compared clinical data from patients infected with H5N6 (n = 19) against data from 2 subtypes of major public health concern, H5N1 (n = 53) and H7N9 (n = 160). To assess immune responses indicative of prognosis, we compared concentrations of serum cytokines/chemokines in patients infected with H5N6, H5N1, H7N9, and 2009 pandemic H1N1 and characterized specific immune responses from 1 surviving and 2 nonsurviving H5N6 patients.

RESULTS

H5N6 patients were found to have higher incidences of lymphopenia and elevated alanine aminotransferase and lactate dehydrogenase levels compared with H5N1 and H7N9 patients. Hypercytokinemia was detected at substantially higher frequencies from H5N6 patients compared to those infected with other AIV subtypes. Evaluation of adaptive immunity showed that both humoral and cellular responses could be detected in the H5N6-infected survivor, but cellular responses were absent in the nonsurvivors. In addition, the surviving patient had lower concentrations of both pro- and anti-inflammatory cytokines/chemokines compared to the nonsurvivors.

CONCLUSIONS

Our results support that H5N6 virus could potentially be a major public health threat, and suggest it is possible that the earlier acquisition of cellular immunity and lower concentrations of cytokines/chemokines contributed to survival in our patient. Analysis of more patient samples will be needed to draw concrete conclusions.

HA-Dependent Tropism of H5N1 and H7N9 Influenza Viruses to Human Endothelial Cells Is Determined by Reduced Stability of the HA, Which Allows the Virus To Cope with Inefficient Endosomal Acidification and Constitutively Expressed IFITM3

Previous studies revealed that certain avian influenza A viruses (IAVs), including zoonotic H5N1 and H7N9 IAVs, infect cultured human lung microvascular endothelial cells (HULEC) more efficiently than other IAVs and that tropism to HULEC is determined by viral hemagglutinin (HA). To characterize mechanisms of HA-mediated endotheliotropism, we used 2:6 recombinant IAVs harboring HAs from distinctive avian and human viruses and found that efficient infection of HULEC correlated with low conformational stability of the HA. We next studied effects on viral infectivity of single-point amino acid substitutions in the HA of 2:6 recombinant virus A/Vietnam/1203/2004-PR8 (H5N1). Substitutions H8Q, H103Y, T315I, and K58₂I (K58I in the HA2 subunit), which increased stability of the HA, markedly reduced viral infectivity for HULEC, whereas substitutions K189N and K218Q, which altered typical H5N1 virus-like receptor specificity and reduced binding avidity of the HA, led to only marginal reduction of infectivity. None of these substitutions affected virus infection in MDCK cells. We confirmed the previous observation of elevated basal expression of IFITM3 protein in HULEC and found that endosomal acidification is less efficient in HULEC than in MDCK cells. In accord with these findings, counteraction of IFITM3-mediated restriction by amphotericin B and reduction of endosomal pH by moderate acidification of the extracellular medium enhanced infectivity of viruses with stable HA for HULEC without significant effect on infectivity for MDCK cells. Collectively, our results indicate that relatively high pH optimum of fusion of the HA of zoonotic H5N1 and H7N9 IAVs allows them to overcome antiviral effects of inefficient endosomal acidification and IFITM3 in human endothelial cells.IMPORTANCE Receptor specificity of the HA of IAVs is known to be a critical determinant of viral cell tropism. Here, we show that fusion properties of the HA may also play a key role in the tropism. Thus, we demonstrate that IAVs having a relatively low pH optimum of fusion cannot efficiently infect human endothelial cells owing to their relatively high endosomal pH and increased expression of fusion-inhibiting IFITM3 protein. These restrictions can be overcome by IAVs with elevated pH of fusion, such as zoonotic H5N1 and H7N9. Our results illustrate that the infectivity of IAVs depends on an interplay between HA conformational stability, endosomal acidification and IFITM3 expression in target cells, and the extracellular pH. Given significant variation of levels of HA stability among animal, human, and zoonotic IAVs, our findings prompt further studies on the fusion-dependent tropism of IAVs to different cell types in humans and its role in viral host range and pathogenicity.

Using evasins to target the chemokine network in inflammation

Inflammation, is driven by a network comprising cytokines, chemokines, their target receptors and leukocytes, and is a major pathologic mechanism that adversely affects organ function in diverse human diseases. Despite being supported by substantial target validation, no successful anti-chemokine therapeutic to treat inflammatory disease has yet been developed. This is in part because of the robustness of the chemokine network, which emerges from a large total chemokine load in disease, promiscuous expression of receptors on leukocytes, promiscuous and synergistic interactions between chemokines and receptors, and feedforward loops created by secretion of chemokines by leukocytes themselves. Many parasites, including viruses, helminths and ticks, evade the chemokine network by producing proteins that bind promiscuously to chemokines or their receptors. Evasins - three small glycoproteins identified in the saliva of the brown dog tick - bind multiple chemokines, and are active in several animal models of inflammatory disease. Over 50 evasin homologs have recently been identified from diverse tick species. Characterization of the chemokine binding patterns of evasins show that several have anti-chemokine activities that extend substantially beyond those previously described. These studies indicate that evasins function at the site of the tick bite by reducing total chemokine load. This not only reduces chemokine signaling to receptors, but also interrupts feedforward loops, thus disabling the chemokine network. Taking the lead from nature, a goal for the development of new anti-chemokine therapeutics would be to reduce the total chemokine load in disease. This could be achieved by administering appropriate evasin combinations or by smaller peptides that mimic evasin action.

H7N9 influenza A virus activation of necroptosis in human monocytes links innate and adaptive immune responses

We previously demonstrated that avian influenza A H7N9 virus preferentially infected CD14⁺ monocyte in human peripheral blood mononuclear cells (PBMCs), which led to apoptosis. To better understand H7N9 pathogenesis in relation to monocyte cell death, we showed here that extensive phosphorylation of mixed lineage kinase domain-like (MLKL) protein occurred concurrently with the activation of caspases-8, -9 and -3 in H7N9-infected monocytes at 6 h post infection (hpi), indicating that apoptosis and necroptosis pathways were simultaneously activated. The apoptotic morphology was readily observed in H7N9-infected monocytes with transmission electron microscopy (TEM), while the pan-caspase inhibitor, IDN6556 (IDN), accelerated cell death through necroptosis as evidenced by the increased level of pMLKL accompanied with cell swelling and plasma membrane rupture. Most importantly, H7N9-induced cell death could only be stopped by the combined treatment of IDN and necrosulfonamide (NSA), a pMLKL membrane translocation inhibitor, but not by individual inhibition of caspase or RIPK3. Our data further showed that activation of apoptosis and necroptosis pathways in monocytes differentially contributed to the immune response of monocytes upon H7N9 infection. Specifically, caspase inhibition significantly enhanced, while RIPK3 inhibition reduced the early expression of type I interferons and cytokine/chemokines in H7N9-infected monocytes. Moreover, culture supernatants from IDN-treated H7N9-infected monocyte promoted the expression of co-stimulatory molecule CD80, CD83 and CD86 on freshly isolated monocytes and monocyte-derived dendritic cells (MDCs) and enhanced the capacity of MDCs to induce CD3⁺ T-cell proliferation in vitro. In contrast, these immune stimulatory effects were abrogated by using culture supernatants from H7N9-infected monocyte with RIPK3 inhibition. In conclusion, our findings indicated that H7N9 infection activated both apoptosis and necroptosis in monocytes. An intact RIPK3 activity is required for upregulation of innate immune responses, while caspase activation suppresses the immune response.

A review on current trends in the treatment of human infection with H7N9-avian influenza A

The H7N9 subtype of avian influenza is an enzootic and airborne virus which caused an influenza outbreak in China. Infected individuals mostly worked with poultry, suggesting H7N9 virus-infected poultry as the primary source of human infection. Significantly increased levels of proinflammatory mediators (chemokines, cytokines) during virus infection could hamper the immune system and aggravate the infection. Severe cases are marked by fulminant pneumonia, acute respiratory distress syndrome (ARDS) and encephalopathy. Left untreated, the condition may rapidly progress to multi-organ failure and death. Reverse transcription polymerase chain reaction (rRT-PCR) is the gold standard diagnostic test for H7N9 avian influenza. Use of neurominidase inhibitor antivirals remain the main treatment. New antivirals are developed to counteract neurominidase inhibitor resistance H7N9 viral strains. Corticosteroid use in viral pneumonia may provoke mortality and longer viral shedding time. Subjects at high risk of contracting avian influenza H7N9 infection are recommended to receive annual seasonal influenza vaccination.

The Streptococcus pyogenes fibronectin/tenascin-binding protein PrtF.2 contributes to virulence in an influenza superinfection

Influenza A virus (IAV) and Streptococcus pyogenes (the group A Streptococcus; GAS) are important contributors to viral-bacterial superinfections, which result from incompletely defined mechanisms. We identified changes in gene expression following IAV infection of A549 cells. Changes included an increase in transcripts encoding proteins with fibronectin-type III (FnIII) domains, such as fibronectin (Fn), tenascin N (TNN), and tenascin C (TNC). We tested the idea that increased expression of TNC may affect the outcome of an IAV-GAS superinfection. To do so, we created a GAS strain that lacked the Fn-binding protein PrtF.2. We found that the wild-type GAS strain, but not the mutant, co-localized with TNC and bound to purified TNC. In addition, adherence of the wild-type strain to IAV-infected A549 cells was greater compared to the prtF.2 mutant. The wild-type strain was also more abundant in the lungs of mice 24 hours after superinfection compared to the mutant strain. Finally, all mice infected with IAV and the prtF.2 mutant strain survived superinfection compared to only 42% infected with IAV and the parental GAS strain, indicating that PrtF.2 contributes to virulence in a murine model of IAV-GAS superinfection.

IFIT1 Expression Patterns Induced by H9N2 Virus and Inactivated Viral Particle in Human Umbilical Vein Endothelial Cells and Bronchus Epithelial Cells

IFIT1 (also known as ISG56) is a member of the interferon-inducible protein with tetratricopeptide repeats (IFITs) family. IFITs are strongly induced by type I interferon (IFN), double-stranded RNA and virus infection. Here, we investigated IFIT1 expression in human umbilical vein endothelial cells (HUVECs) and in human bronchus epithelial cells (BEAS-2Bs) induced by the H9N2 virus and inactivated viral particle at different time points. We also investigated the effect of H9N2 virus and viral particle infection on IFN-α/β production, and assessed whether hemagglutinin or neuraminidase protein induced IFIT1 expression. Results showed that both H9N2 virus infection and viral particle inoculation induced the expression of IFIT1 at mRNA and protein levels in the two cell lines. Hemagglutinin or neuraminidase protein binding alone is not sufficient to induce IFIT1 expression. Surprisingly, the expression patterns of IFIT1 in response to H9N2 virus and viral particles in the two cell lines were opposite, and production kinetics of IFN-α/β also differed. An additional finding was that induction of IFIT1 in response to H9N2 virus infection or viral particle inoculation was more sensitive in HUVECs than in BEAS-2Bs. Our data offers new insight into the innate immune response of endothelial cells to H9N2 virus infection.

Whole transcriptome analysis reveals differential gene expression profile reflecting macrophage polarization in response to influenza A H5N1 virus infection

Background

Avian influenza A H5N1 virus can cause lethal disease in humans. The virus can trigger severe pneumonia and lead to acute respiratory distress syndrome. Data from clinical, in vitro and in vivo suggest that virus-induced cytokine dysregulation could be a contributory factor to the pathogenesis of human H5N1 disease. However, the precise mechanism of H5N1 infection eliciting the unique host response are still not well understood.

Methods

To obtain a better understanding of the molecular events at the earliest time points, we used RNA-Seq to quantify and compare the host mRNA and miRNA transcriptomes induced by the highly pathogenic influenza A H5N1 (A/Vietnam/3212/04) or low virulent H1N1 (A/Hong Kong/54/98) viruses in human monocyte-derived macrophages at 1-, 3-, and 6-h post infection.

Results

Our data reveals that two macrophage populations corresponding to M1 (classically activated) and M2 (alternatively activated) macrophage subtypes respond distinctly to H5N1 virus infection when compared to H1N1 virus or mock infection, a distinction that could not be made from previous microarray studies. When this confounding variable is considered in our statistical model, a clear set of dysregulated genes and pathways emerges specifically in H5N1 virus-infected macrophages at 6-h post infection, whilst was not found with H1N1 virus infection. Furthermore, altered expression of genes in these pathways, which have been previously implicated in viral host response, occurs specifically in the M1 subtype. We observe a significant up-regulation of genes in the RIG-I-like receptor signaling pathway. In particular, interferons, and interferon-stimulated genes are broadly affected. The negative regulators of interferon signaling, the suppressors of cytokine signaling, SOCS-1 and SOCS-3, were found to be markedly up-regulated in the initial round of H5N1 virus replication. Elevated levels of these suppressors could lead to the eventual suppression of cellular antiviral genes, contributing to pathophysiology of H5N1 virus infection.

Conclusions

Our study provides important mechanistic insights into the understanding of H5N1 viral pathogenesis and the multi-faceted host immune responses. The dysregulated genes could be potential candidates as therapeutic targets for treating H5N1 disease.

Electronic supplementary material

The online version of this article (10.1186/s12920-018-0335-0) contains supplementary material, which is available to authorized users.

A pilot study on primary cultures of human respiratory tract epithelial cells to predict patients' responses to H7N9 infection

Avian influenza A(H7N9) virus infections frequently lead to acute respiratory distress syndrome and death in humans. We aimed to investigate whether primary cultures of human respiratory tract epithelial cells are helpful to understand H7N9 virus pathogenesis and tissue tropism, and to evaluate how patient-related characteristics can affect the host's response to infection. Normal human bronchial epithelial cells (isolated from two different donors) and primary epithelial cells (harvested from 27 patients undergoing airway surgery) were experimentally infected with H7N9 and/or H1N1pdm for 72 h. After virus infection, the culture media were collected for viral RNA quantitation and cytokine detection. Both H7N9 and H1N1pdm viruses replicated and induced a cytokine response differently for each donor in the normal human bronchial epithelial model. H7N9 replicated equivalently in epithelial cells harvested from the inferior turbinate and paranasal sinus, and those from the larynx and bronchus, at 72 h post-infection. Viral RNA quantity at 72 h was significantly higher in patients aged 21-64 years than in patients aged ≥ 65 years; however, no effects of sex, medical comorbidities, and obesity were noted. H7N9-infected cultured cells released multiple cytokines within 72 h. Levels of interleukin-1β, interleukin-6, interleukin-8, interferon-γ, and tumor necrosis factor-α were associated differently with patient-related characteristics (such as age, sex, obesity, and medical comorbidities). In the era of precision medicine, these findings illustrate the potential utility of this primary culture approach to predict a host's response to H7N9 infection or to future infection by newly emerging viral infections, and to dissect viral pathogenesis.

Investigation of antiviral state mediated by interferon-inducible transmembrane protein 1 induced by H9N2 virus and inactivated viral particle in human endothelial cells

Background

Endothelial cells are believed to play an important role in response to virus infection. Our previous microarray analysis showed that H9N2 virus infection and inactivated viral particle inoculation increased the expression of interferon-inducible transmembrane protein 1 (IFITM1) in human umbilical vein endothelial cells (HUVECs). In present study, we deeply investigated the expression patterns of IFITM1 and IFITM1-mediated antiviral response induced by H9N2 virus infection and inactivated viral particle inoculation in HUVECs. Epithelial cells that are considered target cells of the influenza virus were selected as a reference control.

Methods

First, we quantified the expression levels of IFITM1 in HUVECs induced by H9N2 virus infection or viral particle inoculation using quantitative real-time PCR and western blot. Second, we observed whether hemagglutinin or neuraminidase affected IFITM1 expression in HUVECs. Finally, we investigated the effect of induced-IFITM1 on the antiviral state in HUVECs by siRNA and activation plasmid transfection.

Results

Both H9N2 virus infection and viral particle inoculation increased the expression of IFITM1 without elevating the levels of interferon-ɑ/β in HUVECs. HA or NA protein binding alone is not sufficient to increase the levels of IFITM1 and interferon-ɑ/β in HUVECs. IFITM1 induced by viral particle inoculation significantly decreased the virus titers in culture supernatants of HUVECs.

Conclusions

Our results showed that inactivated viral particle inoculation increased the expression of IFITM1 at mRNA and protein levels. Moreover, the induction of IFITM1 expression mediated the antiviral state in HUVECs.

Productive replication of avian influenza viruses in chicken endothelial cells is determined by hemagglutinin cleavability and is related to innate immune escape

Endotheliotropism is a hallmark of gallinaceous poultry infections with highly pathogenic avian influenza (HPAI) viruses and a feature that distinguishes HPAI from low pathogenic avian influenza (LPAI) viruses. Here, we used chicken aortic endothelial cells (chAEC) as a novel in vitro infection model to assess the susceptibility, permissiveness, and host response of chicken endothelial cells (EC) to infections with avian influenza (AI) viruses. Our data show that productive replication of AI viruses in chAEC is critically determined by hemagglutinin cleavability, and is thus an exclusive trait of HPAI viruses. However, we provide evidence for a link between limited (i.e. trypsin-dependent) replication of certain LPAI viruses, and the viruses' ability to dampen the antiviral innate immune response in infected chAEC. Strikingly, this cell response pattern was also detected in HPAI virus-infected chAEC, suggesting that viral innate immune escape might be a prerequisite for robust AI virus replication in chicken EC.

Adaptation of influenza A (H7N9) virus in primary human airway epithelial cells

Influenza A (H7N9) is an emerging zoonotic pathogen with pandemic potential. To understand its adaptation capability, we examined the genetic changes and cellular responses following serial infections of A (H7N9) in primary human airway epithelial cells (hAECs). After 35 serial passages, six amino acid mutations were found, i.e. HA (R54G, T160A, Q226L, H3 numbering), NA (K289R, or K292R for N2 numbering), NP (V363V/I) and PB2 (L/R332R). The mutations in HA enabled A(H7N9) virus to bind with higher affinity (from 39.2% to 53.4%) to sialic acid α2,6-galactose (SAα2,6-Gal) linked receptors. A greater production of proinflammatory cytokines in hAECs was elicited at later passages together with earlier peaking at 24 hours post infection of IL-6, MIP-1α, and MCP-1 levels. Viral replication capacity in hAECs maintained at similar levels throughout the 35 passages. In conclusion, during the serial infections of hAECs by influenza A(H7N9) virus, enhanced binding of virion to cell receptors with subsequent stronger innate cell response were noted, but no enhancement of viral replication could be observed. This indicates the existence of possible evolutional hurdle for influenza A(H7N9) virus to transmit efficiently from human to human.

Influenza-Omics and the Host Response: Recent Advances and Future Prospects

Influenza A viruses (IAV) continually evolve and have the capacity to cause global pandemics. Because IAV represents an ongoing threat, identifying novel therapies and host innate immune factors that contribute to IAV pathogenesis is of considerable interest. This review summarizes the relevant literature as it relates to global host responses to influenza infection at both the proteome and transcriptome level. The various-omics infection systems that include but are not limited to ferrets, mice, pigs, and even the controlled infection of humans are reviewed. Discussion focuses on recent advances, remaining challenges, and knowledge gaps as it relates to influenza-omics infection outcomes.

Prevention of Influenza A(H7N9) and Bacterial Infections in Mice Using Intranasal Immunization With Live Influenza Vaccine and the Group B Streptococcus Recombinant Polypeptides

We investigate the protective effect of combined vaccination based on live attenuated influenza vaccine (LAIV) and group B streptococcus (GBS) recombinant polypeptides against potential pandemic H7N9 influenza infection followed by GBS burden. Mice were intranasally immunized using 107 50% egg infectious dose (EID₅₀) of H7N3 LAIV, the mix of the 4 GBS peptides (group B streptococcus vaccine [GBSV]), or combined LAIV + GBSV vaccine. The LAIV raised serum hemagglutination-inhibition antibodies against H7N9 in higher titers than against H7N3. Combined vaccination provided advantageous protection against infections with A/Shanghai/2/2013(H7N9)CDC-RG influenza and serotype II GBS. Combined vaccine significantly improved bacterial clearance from the lungs after infection compared with other vaccine groups. The smallest lung lesions due to combined LAIV + GBSV vaccination were associated with a prevalence of lung interferon-γ messenger RNA expression. Thus, combined viral and bacterial intranasal immunization using H7N3 LAIV and recombinant bacterial polypeptides induced balanced adaptive immune response, providing protection against potential pandemic influenza H7N9 and bacterial complications.

Avian influenza virus A H7N9 infects multiple mononuclear cell types in peripheral blood and induces dysregulated cytokine responses and apoptosis in infected monocytes

Most patients with avian influenza A H7N9 virus (H7N9) infection suffer from severe illness, accompanied by dysregulated cytokine/chemokine response, delayed viral clearance and impaired neutralizing antibody response. Here, we evaluated the role of peripheral blood mononuclear cells (PBMCs) in the pathogenesis of H7N9 infection using an ex vivo infection model. H7N9 infected a significantly higher percentage of PBMCs (23.9 %) than those of avian influenza A H5N1 virus (H5N1) (12.3 %) and pandemic H1N1 virus (pH1N1) (5.5 %) (P<0.01). H7N9 infected significantly more B and T lymphocytes than H5N1. When compared with pH1N1, H7N9-infected PBMCs had significantly higher mRNA levels of proinflammatory cytokines and type I interferons (IFNs) at 6 h post-infection (p.i.), but significantly lower levels of IFN-γ and IP-10 at 12 h p.i. Among the PBMCs, CD14+ monocytes were most permissive to H7N9 infection. The percentage of infected CD14+ monocytes was significantly higher for H7N9 than that of pH1N1, but not significantly different from that of H5N1. H7N9-infected monocytes showed higher expression of MIP-1α, MIP-1β and RANTES than that of pH1N1 at 6 h p.i. H7N9- but not pH1N1-infected monocytes died rapidly via apoptosis. Furthermore, pH1N1- but not H7N9-infected monocytes showed increased expression of the monocyte activation and differentiation markers. Unlike pH1N1, H7N9 showed similar PBMC/monocyte cytokine/chemokine expression profile, monocyte cell death and expression of activation/differentiation markers to H5N1. Besides proinflammatory cytokine activation leading to a cytokine storm, impaired IFN-γ production, rapid monocytic death and lack of monocyte differentiation may affect the ability of H7N9-infected innate immune cells to recruit protective adaptive immunity.

P2Y6 receptors are involved in mediating the effect of inactivated avian influenza virus H5N1 on IL-6 & CXCL8 mRNA expression in respiratory epithelium

One of the key pathophysiologies of H5N1 infection is excessive proinflammatory cytokine response (cytokine storm) characterized by increases in IFN-β, TNF-α, IL-6, CXCL10, CCL4, CCL2 and CCL5 in the respiratory tract. H5N1-induced cytokine release can occur via an infection-independent mechanism, however, detail of the cellular signaling involved is poorly understood. To elucidate this mechanism, the effect of inactivated (β-propiolactone-treated) H5N1 on the cytokine and chemokine mRNA expression in 16HBE14o- human respiratory epithelial cells was investigated. We found that the inactivated-H5N1 increased mRNA for IL-6 and CXCL8 but not TNF-α, CCL5 or CXCL10. This effect of the inactivated-H5N1 was inhibited by sialic acid receptor inhibitor (α-2,3 sialidase), adenosine diphosphatase (apyrase), P2Y receptor (P2YR) inhibitor (suramin), P2Y6R antagonist (MRS2578), phospholipase C inhibitor (U73122), protein kinase C inhibitors (BIM and Gö6976) and cell-permeant Ca2+ chelator (BAPTA-AM). Inhibitors of MAPK signaling, including of ERK1/2 (PD98059), p38 MAPK (SB203580) and JNK (SP600125) significantly suppressed the inactivated-H5N1-induced mRNA expression of CXCL8. On the other hand, the inactivated-H5N1-induced mRNA expression of IL-6 was inhibited by SB203580, but not PD98059 or SP600125, whereas SN-50, an inhibitor of NF-κB, inhibited the effect of virus on mRNA expression of both of IL-6 and CXCL8. Taken together, our data suggest that, without infection, inactivated-H5N1 induces mRNA expression of IL-6 and CXCL8 by a mechanism, or mechanisms, requiring interaction between viral hemagglutinin and α-2,3 sialic acid receptors at the cell membrane of host cells, and involves activation of P2Y6 purinergic receptors.

Role of H7 hemagglutinin in murine infectivity of influenza viruses following ocular inoculation

H7 subtype influenza viruses have demonstrated an ocular tropism in humans, causing conjunctivitis and not respiratory symptoms in many infected individuals. However, the molecular determinants which confer ocular tropism are still poorly understood. Here, we used a murine model of ocular inoculation to demonstrate that H7 influenza viruses are more likely to cause infection following ocular exposure than are non-H7 subtype viruses. We included investigation regarding the potential role of several properties of influenza viruses with murine infectivity following ocular inoculation, including virus lineage, pathogenicity, and HA cleavage site composition. Furthermore, we examined the potential contribution of internal proteins to murine ocular infectivity. These studies establish a link between H7 subtype viruses and the risk of heightened infectivity in a mammalian species following ocular exposure, and support the development of non-traditional inoculation methods and models to best understand the human risk posed by influenza viruses of all subtypes.

Prevailing PA Mutation K356R in Avian Influenza H9N2 Virus Increases Mammalian Replication and Pathogenicity

Adaptation of the viral polymerase complex comprising PB1, PB2, and PA is necessary for efficient influenza A virus replication in new host species. We found that PA mutation K356R (PA-K356R) has become predominant since 2014 in avian H9N2 viruses in China as with seasonal human H1N1 viruses. The same mutation is also found in most human isolates of emergent avian H7N9 and H10N8 viruses whose six internal gene segments are derived from the H9N2 virus. We further demonstrated the mammalian adaptive functionality of the PA-K356R mutation. Avian H9N2 virus with the PA-K356R mutation in human A549 cells showed increased nuclear accumulation of PA and increased viral polymerase activity that resulted in elevated levels of viral transcription and virus output. The same mutant virus in mice also enhanced virus replication and caused lethal infection. In addition, combined mutation of PA-K356R and PB2-E627K, a well-known mammalian adaptive marker, in the H9N2 virus showed further cooperative increases in virus production and severity of infection in vitro and in vivo In summary, PA-K356R behaves as a novel mammalian tropism mutation, which, along with other mutations such as PB2-E627K, might render avian H9N2 viruses adapted for human infection.

IMPORTANCE

Mutations of the polymerase complex (PB1, PB2, and PA) of influenza A virus are necessary for viral adaptation to new hosts. This study reports a novel and predominant mammalian adaptive mutation, PA-K356R, in avian H9N2 viruses and human isolates of emergent H7N9 and H10N8 viruses. We found that PA-356R in H9N2 viruses causes significant increases in virus replication and severity of infection in human cells and mice and that PA-K356R cooperates with the PB2-E627K mutation, a well-characterized human adaptive marker, to exacerbate mammalian infection in vitro and in vivo Therefore, the PA-K356R mutation is a significant adaptation in H9N2 viruses and related H7N9 and H10N8 reassortants toward human infectivity.

A new reassortment of influenza A (H7N9) virus causing human infection in Beijing, 2014

A 73-year-old man was confirmed to have an influenza A (H7N9) virus infection, and the causative agent A/Beijing/02/2014(H7N9) virus was isolated. Genetic and phylogenetic analyses revealed that the virus belonged to a novel genotype, which probably emerged and further reassorted with other H9 or H7 viruses in poultry before transmitting to humans. This virus caused a severe infection with high levels of cytokines and neutralizing antibodies. Eventually, the patient was cured after serially combined treatments. Taken together, our findings indicated that this novel genotype of the human H7N9 virus did not evolve directly from the first Beijing isolate A/Beijing/01/2013(H7N9), suggesting that the H7N9 virus has not obtained the ability for human-to-human transmissibility and the virus only evolves in poultry and then infects human by direct contact. Hence, the major measures to prevent human H7N9 virus infection are still to control and standardize the live poultry trade. Early antiviral treatment with combination therapies, including mechanical ventilation, nutrition support and symptomatic treatment, are effective for H7N9 infection.

Preliminary Proteomic Analysis of A549 Cells Infected with Avian Influenza Virus H7N9 and Influenza A Virus H1N1

A newly emerged H7N9 influenza virus poses high risk to human beings. However, the pathogenic mechanism of the virus remains unclear. The temporal response of primary human alveolar adenocarcinoma epithelial cells (A549) infected with H7N9 influenza virus and H1N1 influenza A virus (H1N1, pdm09) were evaluated using the proteomics approaches (2D-DIGE combined with MALDI-TOF-MS/MS) at 24, 48 and 72 hours post of the infection (hpi). There were 11, 12 and 33 proteins with significant different expressions (P<0.05) at 24, 48 and 72hpi, especially F-actin-capping protein subunit alpha-1 (CAPZA1), Ornithine aminotransferase (OAT), Poly(rC)-binding protein 1 (PCBP1), Eukaryotic translation initiation factor 5A-1 (EIF5A) and Platelet-activating factor acetylhydrolaseⅠb subunit beta (PAFAH1B2) were validated by western-blot analysis. The functional analysis revealed that the differential proteins in A549 cells involved in regulating cytopathic effect. Among them, the down-regulation of CAPZA1, OAT, PCBP1, EIF5A are related to the death of cells infected by H7N9 influenza virus. This is the first time show that the down-regulation of PAFAH1B2 is related to the later clinical symptoms of patients infected by H7N9 influenza virus. These findings may improve our understanding of pathogenic mechanism of H7N9 influenza virus in proteomics.

Avian influenza viruses that cause highly virulent infections in humans exhibit distinct replicative properties in contrast to human H1N1 viruses

Avian influenza viruses present an emerging epidemiological concern as some strains of H5N1 avian influenza can cause severe infections in humans with lethality rates of up to 60%. These have been in circulation since 1997 and recently a novel H7N9-subtyped virus has been causing epizootics in China with lethality rates around 20%. To better understand the replication kinetics of these viruses, we combined several extensive viral kinetics experiments with mathematical modelling of in vitro infections in human A549 cells. We extracted fundamental replication parameters revealing that, while both the H5N1 and H7N9 viruses replicate faster and to higher titers than two low-pathogenicity H1N1 strains, they accomplish this via different mechanisms. While the H7N9 virions exhibit a faster rate of infection, the H5N1 virions are produced at a higher rate. Of the two H1N1 strains studied, the 2009 pandemic H1N1 strain exhibits the longest eclipse phase, possibly indicative of a less effective neuraminidase activity, but causes infection more rapidly than the seasonal strain. This explains, in part, the pandemic strain’s generally slower growth kinetics and permissiveness to accept mutations causing neuraminidase inhibitor resistance without significant loss in fitness. Our results highlight differential growth properties of H1N1, H5N1 and H7N9 influenza viruses.

Mammalian Pathogenesis and Transmission of H7N9 Influenza Viruses from Three Waves, 2013-2015

Three waves of human infection with H7N9 influenza viruses have concluded to date, but only viruses within the first wave (isolated between March and September 2013) have been extensively studied in mammalian models. While second- and third-wave viruses remain closely linked phylogenetically and antigenically, even subtle molecular changes can impart critical shifts in mammalian virulence. To determine if H7N9 viruses isolated from humans during 2013 to 2015 have maintained the phenotype first identified among 2013 isolates, we assessed the ability of first-, second-, and third-wave H7N9 viruses isolated from humans to cause disease in mice and ferrets and to transmit among ferrets. Similar to first-wave viruses, H7N9 viruses from 2013 to 2015 were highly infectious in mice, with lethality comparable to that of the well-studied A/Anhui/1/2013 virus. Second- and third-wave viruses caused moderate disease in ferrets, transmitted efficiently to cohoused, naive contact animals, and demonstrated limited transmissibility by respiratory droplets. All H7N9 viruses replicated efficiently in human bronchial epithelial cells, with subtle changes in pH fusion threshold identified between H7N9 viruses examined. Our results indicate that despite increased genetic diversity and geographical distribution since their initial detection in 2013, H7N9 viruses have maintained a pathogenic phenotype in mammals and continue to represent an immediate threat to public health.

IMPORTANCE

H7N9 influenza viruses, first isolated in 2013, continue to cause human infection and represent an ongoing public health threat. Now entering the fourth wave of human infection, H7N9 viruses continue to exhibit genetic diversity in avian hosts, necessitating continuous efforts to monitor their pandemic potential. However, viruses isolated post-2013 have not been extensively studied, limiting our understanding of potential changes in virus-host adaptation. In order to ensure that current research with first-wave H7N9 viruses still pertains to more recently isolated strains, we compared the relative virulence and transmissibility of H7N9 viruses isolated during the second and third waves, through 2015, in the mouse and ferret models. Our finding that second- and third-wave viruses generally exhibit disease in mammals comparable to that of first-wave viruses strengthens our ability to extrapolate research from the 2013 viruses to current public health efforts. These data further contribute to our understanding of molecular determinants of pathogenicity, transmissibility, and tropism.

Human H7N9 virus induces a more pronounced pro-inflammatory cytokine but an attenuated interferon response in human bronchial epithelial cells when compared with an epidemiologically-linked chicken H7N9 virus

Background

Avian influenza virus H7N9 has jumped species barrier, causing sporadic human infections since 2013. We have previously isolated an H7N9 virus from a patient, and an H7N9 virus from a chicken in a live poultry market where the patient visited during the incubation period. These two viruses were genetically highly similar. This study sought to use a human bronchial epithelial cell line model to infer the virulence of these H7N9 viruses in humans.

Methods

Human bronchial epithelial cell line Calu-3 was infected with two H7N9 viruses (human H7N9-HU and chicken H7N9-CK), a human H5N1 virus and a human 2009 pandemic H1N1 virus. The infected cell lysate was collected at different time points post-infection for the determination of the levels of pro-inflammatory cytokines (tumor necrosis factor α [TNF-α] and interleukin 6 [IL-6]), anti-inflammatory cytokines (interleukin 10 [IL-10] and transforming growth factor beta [TGF-β]), chemokines (interleukin 8 [IL-8] and monocyte chemoattractant protein 1 [MCP-1]), and interferons (interferon β [IFN-β] and interferon lambda 1 [IFNL1]). The viral load in the cell lysate was also measured.

Results

Comparison of the human and chicken H7N9 viruses showed that H7N9-HU induced significantly higher levels of TNF-α at 12 h post-infection, and significantly higher levels of IL-8 from 12 to 48 h post-infection than those of H7N9-CK. However, the level of IFNL1 was lower for H7N9-HU than that of H7N9-CK at 48 h post-infection (P < 0.001). H7N9-HU had significantly higher viral loads than H7N9-CK at 3 and 6 h post-infection. H5N1 induced significantly higher levels of TNF-α, IL-6, IL-8, IL-10 and MCP-1 than those of H7N9 viruses at 48 h post-infection. Conversely, H1N1 induced lower levels of TNF-α, IL-10, MCP-1, IFNL1 and IFN-β when compared with H7N9 viruses at the same time point.

Conclusions

H7N9-HU induced higher levels of pro-inflammatory IL-6 and IL-8 and exhibited a more rapid viral replication than H7N9-CK. However, the level of antiviral IFNL1 was lower for H7N9-HU than H7N9-CK. Our results suggest that the gained properties in modulating human innate immunity by H7N9-HU transformed it to be a more virulent virus in humans than H7N9-CK.

Avian Influenza Viruses, Inflammation, and CD8(+) T Cell Immunity

Avian influenza viruses (AIVs) circulate naturally in wild aquatic birds, infect domestic poultry, and are capable of causing sporadic bird-to-human transmissions. AIVs capable of infecting humans include a highly pathogenic AIV H5N1, first detected in humans in 1997, and a low pathogenic AIV H7N9, reported in humans in 2013. Both H5N1 and H7N9 cause severe influenza disease in humans, manifested by acute respiratory distress syndrome, multi-organ failure, and high mortality rates of 60% and 35%, respectively. Ongoing circulation of H5N1 and H7N9 viruses in wild birds and poultry, and their ability to infect humans emphasizes their epidemic and pandemic potential and poses a public health threat. It is, thus, imperative to understand the host immune responses to the AIVs so we can control severe influenza disease caused by H5N1 or H7N9 and rationally design new immunotherapies and vaccines. This review summarizes our current knowledge on AIV epidemiology, disease symptoms, inflammatory processes underlying the AIV infection in humans, and recent studies on universal pre-existing CD8(+) T cell immunity to AIVs. Immune responses driving the host recovery from AIV infection in patients hospitalized with severe influenza disease are also discussed.

Differences in the epidemiology and virology of mild, severe and fatal human infections with avian influenza A (H7N9) virus

A novel avian influenza A (H7N9) virus caused 5-10 % mild and 30.5 % fatal human infections as of December 10, 2015. In order to investigate the reason for the higher rate of fatal outcome of this infection, this study compared the molecular epidemiology and virology of avian influenza A (H7N9) viruses from mild (N = 14), severe (N = 50) and fatal (N = 35) cases, as well as from non-human hosts (N = 73). The epidemiological results showed that the average age of the people in the mild, severe and fatal groups was 27.6, 52 and 62 years old, respectively (p < 0.001). Males accounted for 42.9 % (6/14), 58.0 % (29/50), and 74.3 % (26/35) of cases in the mild, severe and fatal group respectively (p = 0.094). Median days from onset to start of antiviral treatment were 2, 5 and 7 days in the mild, severe and fatal group, respectively (p = 0.002). The median time from onset to discharge/death was 12, 40 and 19 days in the mild, severe and fatal group, respectively (p < 0.001). Analysis of whole genome sequences showed that PB2 (E627K), NA (R294K) and PA (V100A) mutations were markedly associated with an increased fatality rate, while HA (N276D) and PB2 (N559T) mutations were clearly related to mild cases. There were no differences in the genotypes, adaptation to mammalian hosts, and genetic identity between the three types of infection. In conclusion, advanced age and delayed confirmation of diagnosis and antiviral intervention were risk factors for death. Furthermore, PB2 (E627K), NA (R294K) and PA (V100A) mutations might contribute to a fatal outcome in human H7N9 infection.