Tropism and innate host responses of the 2009 pandemic H1N1 influenza virus in ex vivo and in vitro cultures of human conjunctiva and respiratory tract

Characterization of innate responses to influenza virus infection in a novel lung type I epithelial cell model

Type I alveolar epithelial cells are a replicative niche for influenza in vivo, yet their response to infection is not fully understood. To better characterize their cellular responses, we have created an immortalized murine lung epithelial type I cell line (LET1). These cells support spreading influenza virus infection in the absence of exogenous protease and thus permit simultaneous analysis of viral replication dynamics and host cell responses. LET1 cells can be productively infected with human, swine and mouse-adapted strains of influenza virus and exhibit expression of an antiviral transcriptional programme and robust cytokine secretion. We characterized influenza virus replication dynamics and host responses of lung type I epithelial cells and identified the capacity of epithelial cell-derived type I IFN to regulate specific modules of antiviral effectors to establish an effective antiviral state. Together, our results indicate that the type I epithelial cell can play a major role in restricting influenza virus infection without contribution from the haematopoietic compartment.

Early host responses of seasonal and pandemic influenza A viruses in primary well-differentiated human lung epithelial cells

Replication, cell tropism and the magnitude of the host's antiviral immune response each contribute to the resulting pathogenicity of influenza A viruses (IAV) in humans. In contrast to seasonal IAV in human cases, the 2009 H1N1 pandemic IAV (H1N1pdm) shows a greater tropism for infection of the lung similar to H5N1. We hypothesized that host responses during infection of well-differentiated, primary human bronchial epithelial cells (wd-NHBE) may differ between seasonal (H1N1 A/BN/59/07) and H1N1pdm isolates from a fatal (A/KY/180/10) and nonfatal (A/KY/136/09) case. For each virus, the level of infectious virus and host response to infection (gene expression and apical/basal cytokine/chemokine profiles) were measured in wd-NHBE at 8, 24, 36, 48 and 72 hours post-infection (hpi). At 24 and 36 hpi, KY/180 showed a significant, ten-fold higher titer as compared to the other two isolates. Apical cytokine/chemokine levels of IL-6, IL-8 and GRO were similar in wd-NHBE cells infected by each of these viruses. At 24 and 36 hpi, NHBE cells had greater levels of pro-inflammatory cytokines including IFN-α, CCL2, TNF-α, and CCL5, when infected by pandemic viruses as compared with seasonal. Polarization of IL-6 in wd-NHBE cells was greatest at 36 hpi for all isolates. Differential polarized secretion was suggested for CCL5 across isolates. Despite differences in viral titer across isolates, no significant differences were observed in KY/180 and KY/136 gene expression intensity profiles. Microarray profiles of wd-NHBE cells diverged at 36 hpi with 1647 genes commonly shared by wd-NHBE cells infected by pandemic, but not seasonal isolates. Significant differences were observed in cytokine signaling, apoptosis, and cytoskeletal arrangement pathways. Our studies revealed differences in temporal dynamics and basal levels of cytokine/chemokine responses of wd-NHBE cells infected with each isolate; however, wd-NHBE cell gene intensity profiles were not significantly different between the two pandemic isolates suggesting post-transcriptional or later differences in viral-host interactions.

Pandemic H1N1 influenza A directly induces a robust and acute inflammatory gene signature in primary human bronchial epithelial cells downstream of membrane fusion

Pandemic H1N1 influenza A (H1N1pdm) elicits stronger pulmonary inflammation than previously circulating seasonal H1N1 influenza A (sH1N1), yet mechanisms of inflammatory activation in respiratory epithelial cells during H1N1pdm infection are unclear. We investigated host responses to H1N1pdm/sH1N1 infection and virus entry mechanisms in primary human bronchial epithelial cells in vitro. H1N1pdm infection rapidly initiated a robust inflammatory gene signature (3 h post-infection) not elicited by sH1N1 infection. Protein secretion inhibition had no effect on gene induction. Infection with membrane fusion deficient H1N1pdm failed to induce robust inflammatory gene expression which was rescued with restoration of fusion ability, suggesting H1N1pdm directly triggered the inflammatory signature downstream of membrane fusion. Investigation of intra-virion components revealed H1N1pdm viral RNA (vRNA) triggered a stronger inflammatory phenotype than sH1N1 vRNA. Thus, our study is first to report H1N1pdm induces greater inflammatory gene expression than sH1N1 in vitro due to direct virus-epithelial cell interaction.

Closely related influenza viruses induce contrasting respiratory tract immunopathology

The swine-origin H1N1 virus which emerged in 2009 resulted in the first influenza pandemic of the 21^st century. Although the majority of infections were moderate, a significant proportion of infections were severe and characterized by acute respiratory distress syndrome and pulmonary edema. We compared two isolates from the 2009 H1N1 pandemic; A/California/07/09 (CA/07) and A/Netherlands/602/09 (NL/602) viruses that share greater than 99% sequence identity. Though genetically similar, these viruses exhibit contrasting pathological effects. Mice that were infected with 800 plaque forming unit (PFU) of CA/07 virus rapidly lost weight, which was concurrent with detection of high pulmonary concentrations of MCP-1, MIG, IP-10 and TIMP-1. Initially, severe bronchiolar epithelial necrosis and acute respiratory distress was observed, followed by marked bronchiolar epithelial hyperplasia. Mononuclear cell infiltration was initially localized to perivascular and peribronchiolar interstitium and then spread to adjacent alveoli. Infiltrating cells were phenotypically CD11b^hi, F4/80^lo. In contrast, when mice were infected with 800 PFU of NL/602 virus, minimal weight loss was observed, and concentrations of cytokines in the lung were significantly lower. Inflammation was primarily restricted to the bronchioles and perivascular interstitium with minimal spread to alveoli. Infiltrating cells include foamy macrophages and surface markers were characterized as CD11b^lo/-, F4/80^hi. These two genetically similar viruses can be useful strains with which to investigate immune-regulatory determinants of pathogenesis of influenza virus.

Tropism and innate host responses of a novel avian influenza A H7N9 virus: an analysis of ex-vivo and in-vitro cultures of the human respiratory tract

BACKGROUND

Since March, 2013, an avian-origin influenza A H7N9 virus has caused severe pneumonia in China. The aim of this study was to investigate the pathogenesis of this new virus in human beings.

METHODS

We obtained ex-vivo cultures of the human bronchus, lung, nasopharynx, and tonsil and in-vitro cultures of primary human alveolar epithelial cells and peripheral blood monocyte-derived macrophages. We compared virus tropism and induction of proinflammatory cytokine responses of two human influenza A H7N9 virus isolates, A/Shanghai/1/2013 and A/Shanghai/2/2013; a highly pathogenic avian influenza H5N1 virus; the highly pathogenic avian influenza H7N7 virus that infected human beings in the Netherlands in 2003; the 2009 pandemic influenza H1N1 virus, and a low pathogenic duck H7N9 virus that was genetically different to the human disease causing A H7N9 viruses.

FINDINGS

Both human H7N9 viruses replicated efficiently in human bronchus and lung ex-vivo cultures, whereas duck/H7N9 virus failed to replicate in either. Both human A H7N9 viruses infected both ciliated and non-ciliated human bronchial epithelial cells and replicated to higher titres than did H5N1 (p<0.0001 to 0.0046) and A/Shanghai/1/2013 replicated to higher titres than did H7N7 (p=0.0002-0.01). Both human A H7N9 viruses predominantly infected type II alveolar epithelial cells and alveolar macrophages in the human lung and replicated to higher titres than did H5N1 (p<0.0001 to 0.0078); A/Shanghai/1/2013 replicated to higher titres than did H1N1 (p=0.0052-0.05) and H7N7 (p=0.0031-0.0151). Human H7N9 viruses were less potent inducers of proinflammatory cytokines compared with H5N1 virus.

INTERPRETATION

Collectively, the results suggest that the novel H7N9 viruses are better adapted to infect and replicate in the human conducting and lower airways than are other avian influenza viruses, including H5N1, and pose an important pandemic threat.

FUNDING

Area of Excellence Scheme of the University Grants Committee (AoE/M-12/96), Hong Kong Special Administrative Region.

Infection of swine ex vivo tissues with avian viruses including H7N9 and correlation with glycomic analysis

Objectives

Swine have been regarded as intermediate hosts in the spread of influenza from birds to humans but studies of the sialylated glycans that comprise their respiratory tract have not been extensively studied in the past. This study analyzed the sialylated N‐glycan and O‐glycan profile of swine trachea and lung and correlated this with ex‐vivo infection of swine explants with avian influenza viruses.

Sample

Lungs and tracheal samples were obtained from normal farm and laboratory raised swine and used for ex vivo infection as well as mass spectrometric analysis. Infection of the ex vivo tissues used high pathogenic and low pathogenic avian viruses including the novel H7N9 virus that emerged in China in early 2013.

Main outcome measures

Assessment of successful replication was determined by TCID50 as well as virus immunohistochemistry. The N‐glycan and O‐glycan profiles were measured by MALDI‐TOF and sialylated linkages were determined by sialidase treatment. Lectin binding histochemistry was also performed on formalin fixed tissue samples with positive binding detected by chromogen staining.

Results

The swine respiratory tract glycans differed from the human respiratory tact glycans in two main areas. There was a greater abundance of Gal‐α‐Gal linkages resulting in a relative decrease in sialylated glycans. The swine respiratory tract also had a greater proportion of glycans containing Neu5Gc and Siaα2‐6 glycans than the human respiratory tract. Infection with avian viruses was confined primarily to lung bronchioles rather than trachea and parenchyma.

Conclusions

In contrast to previous studies we found that there was not as much expression of Siaα2‐3 glycans on the surface of the trachea. Infection of Siaα2‐3 binding avian viruses was restricted to the lower respiratory tract bronchioles. This finding may diminish the ability of the swine to act as an intermediary in the transmission of avian viruses to humans.

Epidemiology of pandemic influenza A/H1N1 virus during 2009-2010 in Taiwan

Outbreak of swine-origin influenza A/H1N1 virus (pdmH1N1) occurred in 2009. Taiwanese authorities implemented nationwide vaccinations with pdmH1N1-specific inactivated vaccine as of November 2009. This study evaluates prevalence, HA phylogenetic relationship, and transmission dynamic of influenza A and B viruses in Taiwan in 2009-2010. Respiratory tract specimens were analyzed for influenza A and B viruses. The pdmH1N1 peaked in November 2009, was predominant from August 2009 to January 2010, then sharply dropped in February 2010. Significant prevalence peaks of influenza B in April-June of 2010 and H3N2 virus in July and August were observed. Highest percentage of pdmH1N1- and H3N2-positive cases appeared among 11-15-year-olds; influenza B-positive cases were dominant among those 6-10 years old. Maximum likelihood phylogenetic trees showed 11 unique clusters of pdmH1N1, seasonal H3N2 influenza A and B viruses, as well as transmission clusters and mixed infections of influenza strains in Taiwan. The 2009 pdmH1N1 virus was predominant in Taiwan from August 2009 to January 2010; seasonal H3N2 influenza A and B viruses exhibited small prevalence peaks after nationwide vaccinations. Phylogenetic evidence indicated transmission clusters and multiple independent clades of co-circulating influenza A and B strains in Taiwan.

Carbohydrate determinants in ferret conjunctiva are affected by infection with influenza H1N1 virus

BACKGROUND

Carbohydrates often accomplish as cell-surface receptors for microorganisms and influenza virus preferentially binds to sialic acid through the viral haemagglutinin. The virus may attach not only to the epithelium in the airways, but also to the surface ocular epithelium.

PURPOSE

To decide if ferrets can be used to study virus induced conjunctivitis and to evaluate changes in the conjunctival glycosylation pattern during an influenza attack.

METHODS

Ferrets were infected with H1N1 influenza virus via nasal inoculation. The in situ carbohydrate expressions in eyelid sections from ferrets 0 to 10 days after infection was examined using lectin- and immunohistochemistry.

RESULTS

The conjunctival cells became hypertrophic with appearance of both PAS positive and PAS + Alcian Blue stained cells 5-6 days after inoculation. The binding of three sialic acid detecting lectins were investigated: WGA, MAA2 and SNA1. While none of them stained conjunctival epithelial cells in the non-infected ferrets to any extent, there was a positive conjunctival reaction in the infected ferret after incubation with all three lectins. Binding of a MUC1 antibody that seems to detect sialylated determinants in the mucin molecule indicates that MUC1 is de novo expressed in most of the squamous conjunctival cells at the start of the influenza infection. MUC5AC positive epithelial cells, probably goblet cells, proliferate in the diseased conjunctiva.

CONCLUSION

Nasal inoculation of H1N1 virus to ferrets has an effect on the conjunctival cells and change their expression of glycans. Synthesized glycans are an integral part of the tear film and the present study contributes to reveal the changes that occur in the surface epithelium in the eyelid and thereby to elucidate the pathophysiology of the virus mediated conjunctivitis. Ferrets are suitable animal models to study human conjunctivitis mediated by human influenza virus.

Pandemic H1N1 illness prognosis: evidence from clinical and epidemiological data from the first pandemic wave in São Paulo, Brazil

OBJECTIVES

The pandemic of 2009 H1N1 influenza A emerged in February 2009, with high morbidity and mortality, and rapidly spread globally. São Paulo was among the most affected areas in Brazil. This study compares the clinical and epidemiological characteristics of influenza-like illness between outpatients and hospitalized patients and evaluates the impact of oseltamivir therapy on the outcome of 2009 H1N1 influenza A patients.

METHODS

This is a case series study comparing the clinical and epidemiological characteristics of influenza-like illness between outpatients attended at Hospital São Paulo in August 2009 (the peak of the first pandemic wave) and those patients hospitalized between May and September 2009 (the entire first pandemic wave).

RESULTS

The 1651 patients evaluated were predominantly female (927×686, p<0.001) and aged 31.71±16.42 years, with 148 reporting chronic pulmonary disease. Dyspnea was presented by 381 (23.4%) patients and was more frequent among those aged 30 years or more (p<0.001). Hospitalization occurred at 3.73±2.85 days, and antiviral treatment started 2.27±2.97 days after the onset of first symptoms. A delay of more than 5 days in starting oseltamivir therapy was independently associated with hospitalization (p<0.001), a stay in the ICU (p<0.001) and a higher risk of dying (OR=28.1, 95% CI 2.81-280.2, p=0.007).

CONCLUSION

The 2009 pandemic of H1N1 influenza A affected young adults, presented a significant disease burden and produced severe cases with a significant fatality rate. However, promptly starting specific therapy improved the outcome.

Tropism of and innate immune responses to the novel human betacoronavirus lineage C virus in human ex vivo respiratory organ cultures

Since April 2012, there have been 17 laboratory-confirmed human cases of respiratory disease associated with newly recognized human betacoronavirus lineage C virus EMC (HCoV-EMC), and 7 of them were fatal. The transmissibility and pathogenesis of HCoV-EMC remain poorly understood, and elucidating its cellular tropism in human respiratory tissues will provide mechanistic insights into the key cellular targets for virus propagation and spread. We utilized ex vivo cultures of human bronchial and lung tissue specimens to investigate the tissue tropism and virus replication kinetics following experimental infection with HCoV-EMC compared with those following infection with human coronavirus 229E (HCoV-229E) and severe acute respiratory syndrome coronavirus (SARS-CoV). The innate immune responses elicited by HCoV-EMC were also investigated. HCoV-EMC productively replicated in human bronchial and lung ex vivo organ cultures. While SARS-CoV productively replicated in lung tissue, replication in human bronchial tissue was limited. Immunohistochemistry revealed that HCoV-EMC infected nonciliated bronchial epithelium, bronchiolar epithelial cells, alveolar epithelial cells, and endothelial cells. Transmission electron microscopy showed virions within the cytoplasm of bronchial epithelial cells and budding virions from alveolar epithelial cells (type II). In contrast, there was minimal HCoV-229E infection in these tissues. HCoV-EMC failed to elicit strong type I or III interferon (IFN) or proinflammatory innate immune responses in ex vivo respiratory tissue cultures. Treatment of human lung tissue ex vivo organ cultures with type I IFNs (alpha and beta IFNs) at 1 h postinfection reduced the replication of HCoV-EMC, suggesting a potential therapeutic use of IFNs for treatment of human infection.

Use of ex vivo and in vitro cultures of the human respiratory tract to study the tropism and host responses of highly pathogenic avian influenza A (H5N1) and other influenza viruses

The tropism of influenza viruses for the human respiratory tract is a key determinant of host-range, and consequently, of pathogenesis and transmission. Insights can be obtained from clinical and autopsy studies of human disease and relevant animal models. Ex vivo cultures of the human respiratory tract and in vitro cultures of primary human cells can provide complementary information provided they are physiologically comparable in relevant characteristics to human tissues in vivo, e.g. virus receptor distribution, state of differentiation. We review different experimental models for their physiological relevance and summarize available data using these cultures in relation to highly pathogenic avian influenza H5N1, in comparison where relevant, with other influenza viruses. Transformed continuous cell-lines often differ in important ways to the corresponding tissues in vivo. The state of differentiation of primary human cells (respiratory epithelium, macrophages) can markedly affect virus tropism and host responses. Ex vivo cultures of human respiratory tissues provide a close resemblance to tissues in vivo and may be used to risk assess animal viruses for pandemic threat. Physiological factors (age, inflammation) can markedly affect virus receptor expression and virus tropism. Taken together with data from clinical studies on infected humans and relevant animal models, data from ex vivo and in vitro cultures of human tissues and cells can provide insights into virus transmission and pathogenesis and may provide understanding that leads to novel therapeutic interventions.

Glycomic analysis of human respiratory tract tissues and correlation with influenza virus infection

The first step in influenza infection of the human respiratory tract is binding of the virus to sialic (Sia) acid terminated receptors. The binding of different strains of virus for the receptor is determined by the α linkage of the sialic acid to galactose and the adjacent glycan structure. In this study the N- and O-glycan composition of the human lung, bronchus and nasopharynx was characterized by mass spectrometry. Analysis showed that there was a wide spectrum of both Sia α2-3 and α2-6 glycans in the lung and bronchus. This glycan structural data was then utilized in combination with binding data from 4 of the published glycan arrays to assess whether these current glycan arrays were able to predict replication of human, avian and swine viruses in human ex vivo respiratory tract tissues. The most comprehensive array from the Consortium for Functional Glycomics contained the greatest diversity of sialylated glycans, but was not predictive of productive replication in the bronchus and lung. Our findings indicate that more comprehensive but focused arrays need to be developed to investigate influenza virus binding in an assessment of newly emerging influenza viruses.

This study was performed to determine what possible glycan receptors for influenza were present in the human respiratory tract. We compared the glycans present on existing published glycan arrays with the actual glycans identified in the human respiratory tract by mass spectrometric analysis to determine how representative these arrays would be for potential binding. The most comprehensive array to date only contained approximately half the range of the actual glycans present. Over the past 5 years we have performed ex-vivo infection of 113 bronchial and 185 lung samples with seasonal, avian and swine influenza viruses, and have demonstrated that the lung is able to be infected by all types of influenza viruses but that the bronchus can also be infected by a limited range of avian, swine and seasonal viruses. The key findings are that there is wide spectrum of glycans present in the respiratory tract which can be used by influenza viruses for infection, and the currently available arrays are not predictive of successful infection. Our findings will be of use for researchers in developing more comprehensive and focused arrays for the screening of emerging influenza viruses and bacteria in order to determine their potential threat to humans.

Ocular tropism of respiratory viruses

Respiratory viruses (including adenovirus, influenza virus, respiratory syncytial virus, coronavirus, and rhinovirus) cause a broad spectrum of disease in humans, ranging from mild influenza-like symptoms to acute respiratory failure. While species D adenoviruses and subtype H7 influenza viruses are known to possess an ocular tropism, documented human ocular disease has been reported following infection with all principal respiratory viruses. In this review, we describe the anatomical proximity and cellular receptor distribution between ocular and respiratory tissues. All major respiratory viruses and their association with human ocular disease are discussed. Research utilizing in vitro and in vivo models to study the ability of respiratory viruses to use the eye as a portal of entry as well as a primary site of virus replication is highlighted. Identification of shared receptor-binding preferences, host responses, and laboratory modeling protocols among these viruses provides a needed bridge between clinical and laboratory studies of virus tropism.

Kinetics of viral replication and induction of host responses in ferrets differs between ocular and intranasal routes of inoculation

While influenza viruses are typically considered respiratory pathogens, the ocular system represents a secondary entry point for virus to establish a productive respiratory infection and the location for rare instances of virus-induced conjunctivitis. We used the ferret model to conduct a side-by-side comparison of virus infectivity, kinetics of viral replication, and induction of host responses following inoculation by either the intranasal or ocular routes with two viruses, A/Netherlands/230/03 (H7N7) and A/Panama/2007/99 (H3N2). We show that ocular inoculation resulted in delayed virus replication and reduced levels of proinflammatory cytokine and chemokine transcript in respiratory tract but not ocular tissues compared with intranasally inoculated animals. We identified numerous proinflammatory mediators with known roles in ocular disease elicited in ferret eye tissue following influenza virus infection. These findings provide a greater understanding of the modulation of host responses following different inoculation routes and underscore the risk associated with ocular exposure to influenza viruses.

Infectious salmon anaemia virus infection of Atlantic salmon gill epithelial cells

Infectious salmon anaemia virus (ISAV), a member of the Orthomyxoviridae family, infects and causes disease in farmed Atlantic salmon (Salmo salar L.). Previous studies have shown Atlantic salmon endothelial cells to be the primary targets of ISAV infection. However, it is not known if cells other than endothelial cells play a role in ISAV tropism. To further assess cell tropism, we examined ISAV infection of Atlantic salmon gill epithelial cells in vivo and in vitro. We demonstrated the susceptibility of epithelial cells to ISAV infection. On comparison of primary gill epithelial cell cultures with ISAV permissive fish cell cultures, we found the virus yield in primary gill epithelial cells to be comparable with that of salmon head kidney (SHK)-1 cells, but lower than TO or Atlantic salmon kidney (ASK)-II cells. Light and transmission electron microscopy (TEM) revealed that the primary gill cells possessed characteristics consistent with epithelial cells. Virus histochemistry showed that gill epithelial cells expressed 4-O-acetylated sialic acid which is recognized as the ISAV receptor. To the best of our knowledge, this is the first demonstration of ISAV infection in Atlantic salmon primary gill epithelial cells. This study thus broadens our understanding of cell tropism and transmission of ISAV in Atlantic salmon.

Tropism and infectivity of influenza virus, including highly pathogenic avian H5N1 virus, in ferret tracheal differentiated primary epithelial cell cultures

Tropism and adaptation of influenza viruses to new hosts is partly dependent on the distribution of the sialic acid (SA) receptors to which the viral hemagglutinin (HA) binds. Ferrets have been established as a valuable in vivo model of influenza virus pathogenesis and transmission because of similarities to humans in the distribution of HA receptors and in clinical signs of infection. In this study, we developed a ferret tracheal differentiated primary epithelial cell culture model that consisted of a layered epithelium structure with ciliated and nonciliated cells on its apical surface. We found that human-like (α2,6-linked) receptors predominated on ciliated cells, whereas avian-like (α2,3-linked) receptors, which were less abundant, were presented on nonciliated cells. When we compared the tropism and infectivity of three human (H1 and H3) and two avian (H1 and H5) influenza viruses, we observed that the human influenza viruses primarily infected ciliated cells and replicated efficiently, whereas a highly pathogenic avian H5N1 virus (A/Vietnam/1203/2004) replicated efficiently within nonciliated cells despite a low initial infection rate. Furthermore, compared to other influenza viruses tested, VN/1203 virus replicated more efficiently in cells isolated from the lower trachea and at a higher temperature (37°C) compared to a lower temperature (33°C). VN/1203 virus infection also induced higher levels of immune mediator genes and cell death, and virus was recovered from the basolateral side of the cell monolayer. This ferret tracheal differentiated primary epithelial cell culture system provides a valuable in vitro model for studying cellular tropism, infectivity, and the pathogenesis of influenza viruses.

Localization of pandemic 2009 H1N1 influenza A virus RNA in lung and lymph nodes of fatal influenza cases by in situ hybridization: new insights on virus replication and pathogenesis

BACKGROUND

Pandemic 2009 H1N1 influenza A (pH1N1) virus has caused substantial morbidity and mortality globally and continues to circulate. Although pH1N1 viral antigens have been demonstrated in various human tissues by immunohistochemistry (IHC), cellular localization of pH1N1 RNA in these tissues has largely remained uninvestigated.

OBJECTIVES

To examine the distribution of pH1N1 RNA in tissues of fatal cases in order to understand the virus tissue tropism, replication and disease pathogenesis.

STUDY DESIGN

Formalin-fixed, paraffin embedded autopsy tissues from 21 patients with confirmed pH1N1 infection were analyzed by influenza A IHC and by in situ hybridization (ISH) using DIG-labeled sense (detects viral RNA) and antisense probes (detects positive-stranded mRNA and cRNA) targeting the nucleoprotein gene of pH1N1 virus.

RESULTS

pH1N1 RNA was localized by ISH in 57% of cases while viral antigens were detected by IHC in 76%. However, in cases with a short duration of illness (1-3 days), more cases (69%) were positive by ISH than IHC (62%). Strong ISH staining was detected by antisense probes in the alveolar pneumocytes of the lungs, mucous glands and in lymph nodes. IHC staining of viral antigens was demonstrated in the lung pneumocytes and mucous glands, but no immunostaining was detected in any of the lymph nodes examined.

CONCLUSIONS

This study demonstrates cellular localization of positive-stranded pH1N1 RNA in the lungs, mucous glands and lymph nodes that suggests viral replication in these tissues. The novel ISH assay can be a useful adjunct for the detection of pH1N1 virus in tissues and for pathogenesis studies.

Influenza A(H1N1)pdm09 virus suppresses RIG-I initiated innate antiviral responses in the human lung

Influenza infection is a major cause of morbidity and mortality. Retinoic acid-inducible gene I (RIG-I) is believed to play an important role in the recognition of, and response to, influenza virus and other RNA viruses. Our study focuses on the hypothesis that pandemic H1N1/09 influenza virus alters the influenza-induced proinflammatory response and suppresses host antiviral activity. We first compared the innate response to a clinical isolate of influenza A(H1N1)pdm09 virus, OK/09, a clinical isolate of seasonal H3N2 virus, OK/06, and to a laboratory adapted seasonal H1N1 virus, PR8, using a unique human lung organ culture model. Exposure of human lung tissue to either pandemic or seasonal influenza virus resulted in infection and replication in alveolar epithelial cells. Pandemic virus induces a diminished RIG-I mRNA and antiviral cytokine response than seasonal virus in human lung. The suppression of antiviral response and RIG-I mRNA expression was confirmed at the protein level by ELISA and western blot. We performed a time course of RIG-I and interferon-β (IFN-β) mRNA induction by the two viruses. RIG-I and IFN-β induction by OK/09 was of lower amplitude and shorter duration than that caused by PR8. In contrast, the pandemic virus OK/09 caused similar induction of proinflammatory cytokines, IL-8 and IL-6, at both the transcriptional and translational level as PR8 in human lung. Differential antiviral responses did not appear to be due to a difference in cellular infectivity as immunohistochemistry showed that both viruses infected alveolar macrophages and epithelial cells. These findings show that influenza A(H1N1)pdm09 virus suppresses anti-viral immune responses in infected human lung through inhibition of viral-mediated induction of the pattern recognition receptor, RIG-I, though proinflammatory cytokine induction was unaltered. This immunosuppression of the host antiviral response by pandemic virus may have contributed to the more serious lung infections that occurred in the H1N1 pandemic of 2009.

The epidemiological and public health research response to 2009 pandemic influenza A(H1N1): experiences from Hong Kong

In recent years, Hong Kong has invested in research infrastructure to appropriately respond to novel infectious disease epidemics. Research from Hong Kong made a strong contribution to the international response to the 2009 influenza A (H1N1) pandemic (pH1N1). Summarizing, describing, and reviewing Hong Kong’s response to the 2009 pandemic, this article aimed to identify key elements of a real‐time research response. A systematic search in PubMed and EMBASE for research into the infection dynamics and natural history, impact, or control of pH1N1 in Hong Kong. Eligible articles were analyzed according to their scope. Fifty‐five articles were included in the review. Transmissibility of pH1N1 was similar in Hong Kong to elsewhere, and only a small fraction of infections were associated with severe disease. School closures were effective in reducing pH1N1 transmission, oseltamivir was effective for treatment of severe cases while convalescent plasma therapy has the potential to mitigate future pandemics. There was a rapid and comprehensive research response to pH1N1 in Hong Kong, providing important information on the epidemiology of the novel virus with relevance internationally as well as locally. The scientific knowledge gained through these detailed studies of pH1N1 is now being used to revise and update pandemic plans. The experiences of the research response in Hong Kong could provide a template for the research response to future emerging and reemerging disease epidemics.

Influenza A viruses target type II pneumocytes in the human lung

Background. Highly pathogenic avian H5N1 influenza viruses preferentially infect alveolar type II pneumocytes in human lung. However, it is unknown whether this cellular tropism contributes to high viral virulence because the primary target cells of other influenza viruses have not been systematically studied.

Methods. We provide the first comparison of the replication, tropism, and cytokine induction of human, highly pathogenic avian influenza A virus subtype H5N1 and other animal influenza A viruses in primary human lung organ cultures.

Results. Subytpe H5N1 and human-adapted subtype H1N1 and H3N2 viruses replicated efficiently in the lung tissue, whereas classic swine and low-pathogenicity avian viruses propagated only poorly. Nevertheless, all viruses examined were detected almost exclusively in type II pneumocytes, with a minor involvement of alveolar macrophages. Infection with avian viruses that have a low and high pathogenicity provoked a pronounced induction of cytokines and chemokines, while human and pandemic H1N1-2009 viruses triggered only weak responses.

Conclusions. These findings show that differences in the pathogenic potential of influenza A viruses in the human lung cannot be attributed to a distinct cellular tropism. Rather, high or low viral pathogenicity is associated with a strain-specific capacity to productively replicate in type II pneumocytes and to cope with the induced cytokine response.

Molecular imaging reveals a progressive pulmonary inflammation in lower airways in ferrets infected with 2009 H1N1 pandemic influenza virus

Molecular imaging has gained attention as a possible approach for the study of the progression of inflammation and disease dynamics. Herein we used [(18)F]-2-deoxy-2-fluoro-D-glucose ([(18)F]-FDG) as a radiotracer for PET imaging coupled with CT (FDG-PET/CT) to gain insight into the spatiotemporal progression of the inflammatory response of ferrets infected with a clinical isolate of a pandemic influenza virus, H1N1 (H1N1pdm). The thoracic regions of mock- and H1N1pdm-infected ferrets were imaged prior to infection and at 1, 2, 3 and 6 days post-infection (DPI). On 1 DPI, FDG-PET/CT imaging revealed areas of consolidation in the right caudal lobe which corresponded with elevated [(18)F]-FDG uptake (maximum standardized uptake values (SUVMax), 4.7-7.0). By days 2 and 3, consolidation (CT) and inflammation ([(18)F]-FDG) appeared in the left caudal lobe. By 6 DPI, CT images showed extensive areas of patchy ground-glass opacities (GGO) and consolidations with the largest lesions having high SUVMax (6.0-7.6). Viral shedding and replication were detected in most nasal, throat and rectal swabs and nasal turbinates and lungs on 1, 2 and 3 DPI, but not on day 7, respectively. In conclusion, molecular imaging of infected ferrets revealed a progressive consolidation on CT with corresponding [(18)F]-FDG uptake. Strong positive correlations were measured between SUVMax and bronchiolitis-related pathologic scoring (Spearman's ρ = 0.75). Importantly, the extensive areas of patchy GGO and consolidation seen on CT in the ferret model at 6 DPI are similar to that reported for human H1N1pdm infections. In summary, these first molecular imaging studies of lower respiratory infection with H1N1pdm show that FDG-PET can give insight into the spatiotemporal progression of the inflammation in real-time.

Pandemic (H1N1) 2009 in captive cheetah

We describe virus isolation, full genome sequence analysis, and clinical pathology in ferrets experimentally inoculated with pandemic (H1N1) 2009 virus recovered from a clinically ill captive cheetah that had minimal human contact. Evidence of reverse zoonotic transmission by fomites underscores the substantial animal and human health implications of this virus.

Comparison of ocular findings in patients with H1N1 influenza infection versus patients receiving influenza vaccine during a pandemic

AIM

To evaluate ocular findings during the pandemic influenza A (H1N1) and after vaccination for the same strain.

PATIENTS AND METHODS

This study was conducted on 89 patients with H1N1 influenza infection (group 1) and 28 subjects who received vaccination for H1N1 (group 2). All patients were subjected to history taking, ophthalmological examination, fundus examination, conjunctival impression cytology and conjunctival swabs.

RESULTS

The patients' age ranged between 5 and 60 years (19.25 ± 11.70 years). Group 1 included 43 (48.1%) males and 46 (51.9%) females, while group 2 included 13 (46.43%) males and 15 (53.57%) females. The most common ocular finding of patients in group 1 was bilateral acute conjunctivitis in 58 cases (65.17%), while in group 2, we found 3 (10.71%) cases of mild conjunctivitis, and 2 (7.14%) cases of moderate conjunctivitis. Retinopathy, uveal affection, and optic neuritis were not statistically different between the 2 groups. Impression cytology of the conjunctiva for group 1 showed squamous metaplasia grade 3 with enlargement of epithelial cells, and fragmentation of the nucleus which is similar to virus-infected structural changes.

CONCLUSION

Pandemic influenza H1N1 was able to induce different ocular manifestations including acute conjunctivitis, retinopathy, uveal effusion syndrome and optic neuritis.

Influenza virus respiratory infection and transmission following ocular inoculation in ferrets

While influenza viruses are a common respiratory pathogen, sporadic reports of conjunctivitis following human infection demonstrates the ability of this virus to cause disease outside of the respiratory tract. The ocular surface represents both a potential site of virus replication and a portal of entry for establishment of a respiratory infection. However, the properties which govern ocular tropism of influenza viruses, the mechanisms of virus spread from ocular to respiratory tissue, and the potential differences in respiratory disease initiated from different exposure routes are poorly understood. Here, we established a ferret model of ocular inoculation to explore the development of virus pathogenicity and transmissibility following influenza virus exposure by the ocular route. We found that multiple subtypes of human and avian influenza viruses mounted a productive virus infection in the upper respiratory tract of ferrets following ocular inoculation, and were additionally detected in ocular tissue during the acute phase of infection. H5N1 viruses maintained their ability for systemic spread and lethal infection following inoculation by the ocular route. Replication-independent deposition of virus inoculum from ocular to respiratory tissue was limited to the nares and upper trachea, unlike traditional intranasal inoculation which results in virus deposition in both upper and lower respiratory tract tissues. Despite high titers of replicating transmissible seasonal viruses in the upper respiratory tract of ferrets inoculated by the ocular route, virus transmissibility to naïve contacts by respiratory droplets was reduced following ocular inoculation. These data improve our understanding of the mechanisms of virus spread following ocular exposure and highlight differences in the establishment of respiratory disease and virus transmissibility following use of different inoculation volumes and routes.

Most infections with influenza virus result in respiratory disease. However, influenza viruses of the H7 subtype frequently cause ocular and not respiratory symptoms during human infection, demonstrating that the eye represents an alternate location for influenza viruses to infect humans. Using a ferret model, we studied the ability of influenza viruses to cause disease following ocular inoculation. We found that both human and avian influenza viruses could use the eye as a portal of entry to establish a respiratory infection in ferrets. Influenza viruses were also detected in ocular samples taken from ferrets during virus infection. We identified that influenza viruses spread to different tissues in ferrets when inoculated by ocular or respiratory routes, and that these differences affected the transmissibility of influenza viruses in this model. This study is the first to confirm that virus can spread from the eye to the respiratory tract in a replication-independent manner, and offers greater insight in understanding the ability of influenza viruses of all subtypes to cause human infection by the ocular route.

Restored PB1-F2 in the 2009 pandemic H1N1 influenza virus has minimal effects in swine

PB1-F2 is an 87- to 90-amino-acid-long protein expressed by certain influenza A viruses. Previous studies have shown that PB1-F2 contributes to virulence in the mouse model; however, its role in natural hosts-pigs, humans, or birds-remains largely unknown. Outbreaks of domestic pigs infected with the 2009 pandemic H1N1 influenza virus (pH1N1) have been detected worldwide. Unlike previous pandemic strains, pH1N1 viruses do not encode a functional PB1-F2 due to the presence of three stop codons resulting in premature truncation after codon 11. However, pH1N1s have the potential to acquire the full-length form of PB1-F2 through mutation or reassortment. In this study, we assessed whether restoring the full-length PB1-F2 open reading frame (ORF) in the pH1N1 background would have an effect on virus replication and virulence in pigs. Restoring the PB1-F2 ORF resulted in upregulation of viral polymerase activity at early time points in vitro and enhanced virus yields in porcine respiratory explants and in the lungs of infected pigs. There was an increase in the severity of pneumonia in pigs infected with isogenic virus expressing PB1-F2 compared to the wild-type (WT) pH1N1. The extent of microscopic pneumonia correlated with increased pulmonary levels of alpha interferon and interleukin-1β in pigs infected with pH1N1 encoding a functional PB1-F2 but only early in the infection. Together, our results indicate that PB1-F2 in the context of pH1N1 moderately modulates viral replication, lung histopathology, and local cytokine response in pigs.

Emerged HA and NA mutants of the pandemic influenza H1N1 viruses with increasing epidemiological significance in Taipei and Kaohsiung, Taiwan, 2009-10

The 2009 influenza pandemic provided an opportunity to observe dynamic changes of the hemagglutinin (HA) and neuraminidase (NA) of pH1N1 strains that spread in two metropolitan areas -Taipei and Kaohsiung. We observed cumulative increases of amino acid substitutions of both HA and NA that were higher in the post–peak than in the pre-peak period of the epidemic. About 14.94% and 3.44% of 174 isolates had one and two amino acids changes, respective, in the four antigenic sites. One unique adaptive mutation of HA2 (E374K) was first detected three weeks before the epidemic peak. This mutation evolved through the epidemic, and finally emerged as the major circulated strain, with significantly higher frequency in the post-peak period than in the pre-peak (64.65% vs 9.28%, p<0.0001). E374K persisted until ten months post-nationwide vaccination without further antigenic changes (e.g. prior to the highest selective pressure). In public health measures, the epidemic peaked at seven weeks after oseltamivir treatment was initiated. The emerging E374K mutants spread before the first peak of school class suspension, extended their survival in high-density population areas before vaccination, dominated in the second wave of class suspension, and were fixed as herd immunity developed. The tempo-spatial spreading of E374K mutants was more concentrated during the post–peak (p = 0.000004) in seven districts with higher spatial clusters (p<0.001). This is the first study examining viral changes during the naïve phase of a pandemic of influenza through integrated virological/serological/clinical surveillance, tempo-spatial analysis, and intervention policies. The vaccination increased the percentage of E374K mutants (22.86% vs 72.34%, p<0.001) and significantly elevated the frequency of mutations in Sa antigenic site (2.36% vs 23.40%, p<0.001). Future pre-vaccination public health efforts should monitor amino acids of HA and NA of pandemic influenza viruses isolated at exponential and peak phases in areas with high cluster cases.

Immunomodulatory therapy for severe influenza

Influenza A virus is a significant cause of morbidity and mortality worldwide. Severe influenza is recognized as a clinical syndrome, characterized by hyperinduction of proinflammatory cytokine production, otherwise known as hypercytokinemia or a 'cytokine storm'. Research focused on therapeutics to modulate influenza virus-induced inflammation is currently underway. In this review, we discuss the limitations of current antiviral drug treatment strategies, describe the influenza viral and host pathogenicity determinants, and present the evidence supporting the use of immunomodulatory therapy to target the host inflammatory response as a means to improve clinical outcome in severe influenza. We then review the experimental data on investigational immunomodulatory agents targeting the host inflammatory response in severe influenza, including anti-TNF therapy, statins, glucocorticoids, cyclooxygenase-2 inhibitors, macrolides, peroxisome proliferator-activated receptor agonists, AMP-activated protein kinase agonists and high mobility group box 1 antagonists. We then conclude with a rationale for the use of mesenchymal stromal (stem) cells and angiopoietin-1 therapy against deleterious influenza-induced host responses that mediate end-organ injury and dysfunction.

The 2009 pandemic influenza virus: where did it come from, where is it now, and where is it going?

Around 2008 or 2009, an influenza A virus that had been circulating undetected in swine entered human population. Unlike most swine influenza infections of humans, this virus established sustained human-to-human transmission, leading to a global pandemic. The virus responsible, 2009 pandemic H1N1 (H1N1pdm), is the result of multiple reassortment events that brought together genomic segments from classical H1N1 swine influenza virus, human seasonal H3N2 influenza virus, North American avian influenza virus, and Eurasian avian-origin swine influenza viruses. Genetically, H1N1pdm possesses a number of unusual features, although the genomic characteristics that permitted sustained human-to-human transmission are yet unclear. Human infection with H1N1pdm has generally resulted in low mortality, although certain subgroups (including pregnant women, people with some chronic medical conditions, morbidly obese individuals, and immunosuppressed people) have significantly higher risk of severe disease. As H1N1pdm has spread throughout the human population it continued to evolve. It has also reentered the swine population as a circulating pathogen, and has been transiently identified in other species such as turkeys, cats, and domestic ferrets. Most genetic changes in H1N1pdm to date have not been clearly linked to changes in antigenicity, disease severity, antiviral drug resistance, or transmission efficiency. However, the rapid evolution rate characteristic of influenza viruses suggests that changes in antigenicity are inevitable in future years. Experience with this first pandemic of twenty-first century reemphasizes the importance of influenza surveillance in animals as well as humans, and offers lessons to develop and enhance our ability to identify potentially pandemic influenza viruses in the future.

Pulmonary manifestation of novel swine-origin influenza A (H1N1) virus (S-OIV) infection in immunocompromised patients: initial findings with multidetector computed tomography

OBJECTIVE

To describe initial multidetector computed tomographic (MDCT) findings of novel swine-origin influenza A (H1N1) virus (S-OIV) infection in immunocompromised patients and to evaluate whether or not identification of certain abnormalities can help predict patients who are at risk for a severe clinical course.

SUBJECTS AND METHODS

This retrospective study included 13 patients with confirmed S-OIV infection suffering from an underlying immunodeficiency or who were receiving immunosuppressive therapy. All patients underwent MDCT of the thorax due to respiratory distress. All data were read by two independent radiologists who described the type and pattern of opacities, distribution and extent of the abnormalities observed. Adverse outcome measures were defined as acute respiratory distress syndrome with the need for mechanical ventilation, extracorporeal membrane oxygenation or death.

RESULTS

MDCT revealed pulmonary manifestations in 12 (92%) of 13 individuals. Six (50%) patients showed an adverse outcome with development of acute respiratory distress syndrome, 4 of these died. The most common findings were ground-glass opacities (10/12; 83%) and pulmonary consolidation (7/12; 58%) predominantly with a bilateral distribution. Reticular pattern and a tree-in-bud appearance were found in 3/12 (25%), respectively. Bilateral opacities with extensive involvement of the lung parenchyma were most predictive of a severe clinical course.

CONCLUSION

The MDCT scan in immunocompromised patients with confirmed S-OIV infection frequently revealed pulmonary abnormalities, which included ground-glass opacities and consolidations. Therefore, prediction of an adverse clinical outcome could be made in patients with MDCT findings demonstrating bilateral extensive consolidations, often combined with ground-glass opacities.

H5N1 influenza virus-induced mediators upregulate RIG-I in uninfected cells by paracrine effects contributing to amplified cytokine cascades

Highly pathogenic avian influenza H5N1 viruses cause severe disease in humans, and dysregulation of cytokine responses is believed to contribute to the pathogenesis of human H5N1 disease. However, mechanisms leading to the increased induction of proinflammatory cytokines by H5N1 viruses are poorly understood. We show that the innate sensing receptor RIG-I is involved in interferon regulatory factor 3 (IRF3), NF-κB nuclear translocation, p38 activation, and the subsequent interferon (IFN) β, IFN-λ1, and tumor necrosis factor α induction during H5N1 infection. Soluble mediators from H5N1-infected human macrophages upregulate RIG-I, MDA5, and TLR3 to much higher levels than those from seasonal H1N1 in uninfected human macrophages and alveolar epithelial cells via paracrine IFNAR1/JAK but not IFN-λ receptor signaling. Compared with H1N1 virus-induced mediators, H5N1 mediators markedly enhance the cytokine response to PolyIC and to both seasonal and H5N1 virus infection in a RIG-I-dependent manner. Thus, sensitizing neighboring cells by upregulation of RIG-I contributes to the amplified cytokine cascades during H5N1 infection.

Pneumonia induced by swine-origin influenza A (H1N1) infection: chest computed tomography findings in children

PURPOSE

The purpose of this study was to determine the features of chest computed tomography (CT) in children with swine-origin influenza A (H1N1) virus (S-OIV).

MATERIALS AND METHODS

The study population consisted of 16 children with laboratory-confirmed S-OIV infection (12 boys, 4 girls), with an age range of 5-10 years (mean 6.3 years). Pneumonia was suspected in these patients based on clinical features or confirmed by radiography. All subjects underwent CT for close evaluation of pneumonia, including characteristics, distribution, extent, and other findings such as pleural effusion, pneumothorax, and pneumomediastinum.

RESULTS

The predominant CT finding was consolidation plus ground-grass opacity (GGO) (11/16, 69%). The consolidation-dominant pattern was found in 10 of 16 (66%) patients, and 1 (6%) was GGO-dominant. One (6%) had only GGO. In all, 7 of the 16 patients had segmental or lobar consolidation. Abnormal opacities were primarily distributed in the central lung zone (8/16, 50%) and were multifocal (15/16, 94%). Four showed atelectasis (4/16, 25%). Pneumomediastinum was observed in 4 of 16 (25%). One patient had negative radiographic findings but was positive on CT.

CONCLUSION

Multifocal consolidation with central distribution is a common CT finding in children with S-OIV, but there are few GGO-dominant cases. Widespread consolidation (segmental or lobar) is also common.

Influenza associated mortality in the subtropics and tropics: results from three Asian cities

Influenza has been well documented to significantly contribute to winter increase of mortality in the temperate countries, but its severity in the subtropics and tropics was not recognized until recently and geographical variations of disease burden in these regions remain poorly understood. In this study, we applied a standardized modeling strategy to the mortality and virology data from three Asian cities: subtropical Guangzhou and Hong Kong, and tropical Singapore, to estimate the disease burden of influenza in these cities. We found that influenza was associated with 10.6, 13.4 and 8.3 deaths per 100,000 population in Guangzhou, Hong Kong and Singapore, respectively. The annual rates of excess deaths in the elders were estimated highest in Guangzhou and lowest in Singapore. The excess death rate attributable to A/H1N1 subtype was found slightly higher than the rates attributable to A/H3N2 during the study period of 2004-2006 based on the data from Hong Kong and Guangzhou. Our study revealed a geographical variation in the disease burden of influenza in these subtropical and tropical cities. These results highlight a need to explore the determinants for severity of seasonal influenza.

Cytokine response patterns in severe pandemic 2009 H1N1 and seasonal influenza among hospitalized adults

Background

Studying cytokine/chemokine responses in severe influenza infections caused by different virus subtypes may improve understanding on pathogenesis.

Methods

Adults hospitalized for laboratory-confirmed seasonal and pandemic 2009 A/H1N1 (pH1N1) influenza were studied. Plasma concentrations of 13 cytokines/chemokines were measured at presentation and then serially, using cytometric-bead-array with flow-cytometry and ELISA. PBMCs from influenza patients were studied for cytokine/chemokine expression using ex-vivo culture (Whole Blood Assay,±PHA/LPS stimulation). Clinical variables were prospectively recorded and analyzed.

Results

63 pH1N1 and 53 seasonal influenza patients were studied. pH1N1 patients were younger (mean±S.D. 42.8±19.2 vs 70.5±16.7 years), and fewer had comorbidities. Respiratory/cardiovascular complications were common in both groups (71.4% vs 81.1%), although severe pneumonia with hypoxemia (54.0% vs 28.3%) and ICU admissions (25.4% vs 1.9%) were more frequent with pH1N1. Hyperactivation of the proinflammatory cytokines IL-6, CXCL8/IL-8, CCL2/MCP-1 and sTNFR-1 was found in pH1N1 pneumonia (2–15 times normal) and in complicated seasonal influenza, but not in milder pH1N1 infections. The adaptive-immunity (Th1/Th17)-related CXCL10/IP-10, CXCL9/MIG and IL-17A however, were markedly suppressed in severe pH1N1 pneumonia (2–27 times lower than seasonal influenza; P−values<0.01). This pattern was further confirmed with serial measurements. Hypercytokinemia tended to be sustained in pH1N1 pneumonia, associated with a slower viral clearance [PCR-negativity: day 3–4, 55% vs 85%; day 6–7, 67% vs 100%]. Elevated proinflammatory cytokines, particularly IL-6, predicted ICU admission (adjusted OR 12.6, 95%CI 2.6–61.5, per log₁₀unit increase; P = 0.002), and correlated with fever, tachypnoea, deoxygenation, and length-of-stay (Spearman's rho, P-values<0.01) in influenza infections. PBMCs in seasonal influenza patients were activated and expressed cytokines ex vivo (e.g. IL-6, CXCL8/IL-8, CCL2/MCP-1, CXCL10/IP-10, CXCL9/MIG); their ‘responsiveness’ to stimuli was shown to change dynamically during the illness course.

Conclusions

A hyperactivated proinflammatory, but suppressed adaptive-immunity (Th1/Th17)-related cytokine response pattern was found in severe pH1N1 pneumonia, different from seasonal influenza. Cytokine/immune-dysregulation may be important in its pathogenesis.

Sialylated glycans and mucins in the lacrimal gland and eyelid of man and pig. Potential receptors for pathogenic microorganisms

The conjunctiva of the eyelid is coated by secretion products from the lacrimal and eyelid glands, and by mucins produced by conjunctival goblet cells, which together form a glycoprotein-rich layer that lubricates and protects the surface of the eye. However, these ocular carbohydrates may also act as adhesives for viruses and bacteria and thereby facilitate their colonization. This paper provides histochemical demonstration of the in situ localization of such carbohydrate receptors in the form of sialylated glycans and mucins in the lacrimal and eyelid glands and conjunctiva from both humans and pigs. The pig is included in this study because viruses of swine origin may be capable of transmission to humans. We found that the human and pig ocular surfaces contain receptors for bacteria and viruses in the form of mucins (both membrane bound and secreted) and carbohydrates terminating in Sialylα2-6Gal epitopes and to a lesser degree in Sialylα2-3Gal. The glycosylation of the human soft palate could indicate a mucinous route for the spread of microorganisms from the eye via the nasolacrimal duct to the nasopharynx and thus to the upper part of the respiratory tract.

Effect of D222G mutation in the hemagglutinin protein on receptor binding, pathogenesis and transmissibility of the 2009 pandemic H1N1 influenza virus

Influenza viruses isolated during the 2009 H1N1 pandemic generally lack known molecular determinants of virulence associated with previous pandemic and highly pathogenic avian influenza viruses. The frequency of the amino acid substitution D222G in the hemagglutinin (HA) of 2009 H1N1 viruses isolated from severe but not mild human cases represents the first molecular marker associated with enhanced disease. To assess the relative contribution of this substitution in virus pathogenesis, transmission, and tropism, we introduced D222G by reverse genetics in the wild-type HA of the 2009 H1N1 virus, A/California/04/09 (CA/04). A dose-dependent glycan array analysis with the D222G virus showed a modest reduction in the binding avidity to human-like (α2-6 sialylated glycan) receptors and an increase in the binding to avian-like (α2-3 sialylated glycan) receptors in comparison with wild-type virus. In the ferret pathogenesis model, the D222G mutant virus was found to be similar to wild-type CA/04 virus with respect to lethargy, weight loss and replication efficiency in the upper and lower respiratory tract. Moreover, based on viral detection, the respiratory droplet transmission properties of these two viruses were found to be similar. The D222G virus failed to productively infect mice inoculated by the ocular route, but exhibited greater viral replication and weight loss than wild-type CA/04 virus in mice inoculated by the intranasal route. In a more relevant human cell model, D222G virus replicated with delayed kinetics compared with wild-type virus but to higher titer in human bronchial epithelial cells. These findings suggest that although the D222G mutation does not influence virus transmission, it may be considered a molecular marker for enhanced replication in certain cell types.

Tissue tropism of swine influenza viruses and reassortants in ex vivo cultures of the human respiratory tract and conjunctiva

The 2009 pandemic influenza H1N1 (H1N1pdm) virus was generated by reassortment of swine influenza viruses of different lineages. This was the first influenza pandemic to emerge in over 4 decades and the first to occur after the realization that influenza pandemics arise from influenza viruses of animals. In order to understand the biological determinants of pandemic emergence, it is relevant to compare the tropism of different lineages of swine influenza viruses and reassortants derived from them with that of 2009 pandemic H1N1 (H1N1pdm) and seasonal influenza H1N1 viruses in ex vivo cultures of the human nasopharynx, bronchus, alveoli, and conjunctiva. We hypothesized that virus which can transmit efficiently between humans replicated well in the human upper airways. As previously reported, H1N1pdm and seasonal H1N1 viruses replicated efficiently in the nasopharyngeal, bronchial, and alveolar epithelium. In contrast, representative viruses from the classical swine (CS) (H1N1) lineage could not infect human respiratory epithelium; Eurasian avian-like swine (EA) (H1N1) viruses only infected alveolar epithelium and North American triple-reassortant (TRIG) viruses only infected the bronchial epithelium albeit inefficiently. Interestingly, a naturally occurring triple-reassortant swine virus, A/SW/HK/915/04 (H1N2), with a matrix gene segment of EA swine derivation (i.e., differing from H1N1pdm only in lacking a neuraminidase [NA] gene of EA derivation) readily infected and replicated in human nasopharyngeal and bronchial epithelia but not in the lung. A recombinant sw915 with the NA from H1N1pdm retained its tropism for the bronchus and acquired additional replication competence for alveolar epithelium. In contrast to H1N1pdm, none of the swine viruses tested nor seasonal H1N1 had tropism in human conjunctiva. Recombinant viruses generated by swapping the surface proteins (hemagglutinin and NA) of H1N1pdm and seasonal H1N1 virus demonstrated that these two gene segments together are key determinants of conjunctival tropism. Overall, these findings suggest that ex vivo cultures of the human respiratory tract provide a useful biological model for assessing the human health risk of swine influenza viruses.

Report of the 'mechanisms of lung injury and immunomodulator interventions in influenza' workshop, 21 March 2010, Ventura, California, USA

Please cite this paper as: Howard et al. (2011) Report of the ‘Mechanisms of lung injury and immunomodulator interventions in influenza’ workshop, 21 March 2010, Ventura, California, USA*. Influenza and Other Respiratory Viruses 5(6), 453–e475.

The clinical course of influenza and the extent of lung injury are determined by both viral and host factors, as well as sometimes secondary bacterial infections and exacerbations of underlying conditions. The balance between viral replication and the host immune responses is central to disease pathogenesis, and the extent of lung injury in severe influenza infections may be due in part to overly exuberant or dysregulated innate inflammatory responses or sometimes deficient responses. Acute respiratory distress syndrome (ARDS) is the principal cause of respiratory failure associated with severe influenza. ARDS can be triggered by both direct lung insults (e.g. respiratory pathogens) and systemic insults (e.g. sepsis), and the lung damage is exacerbated by the inflammatory response associated with either infectious or non‐infectious insults. This workshop aimed to review the current understanding of lung injury in acute influenza and describe cellular and molecular mechanisms of lung injury that are common to influenza and infections by other respiratory pathogens. In addition, therapeutic agents that target host response proteins and pathways were identified and investigational agents in development reviewed. A logical strategy would be to combine antiviral treatment with drugs that modify excessive host responses or supplement deficient ones. However, a better understanding of common cell signalling pathways associated with acute lung injury caused by influenza and other pathogens is necessary to understand immunopathologic causes of lung injury. This will help determine which immunomodulatory interventions might be useful, and to predict the appropriate timing and consequences of their use.

Extracorporeal membrane oxygenation in the context of the 2009 H1N1 influenza A pandemic

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) incorporates surgical techniques as adjuncts in the management of refractory respiratory dysfunction. For many years, its primary application was for support of neonatal infants in cardiorespiratory failure. As the 2009 H1N1 influenza A pandemic developed, more reports came in of severe respiratory dysfunction and even death that seemed to be occurring preferentially in younger adults. Centers with the capability began to use ECMO to salvage these patients.

RESULTS

The H1N1 virus is a subtype of influenza A. The hemagglutinin receptor binding is similar to that of the seasonal influenza virus, but 2009 H1N1 also binds to α2,3-linked receptors, which are found in the conjunctivae, distal airways, and alveolar pneumocytes. Influenza viruses elude host immune responses through drift and shift in the hemagglutinin (HA) and neuraminidase (NA) proteins. The incubation period ranges from 1-7 days. The majority of patients present with fever and cough, but a broad spectrum of clinical syndromes has been reported, and laboratory testing remains the mainstay of diagnosis. Most patients recover within a week without treatment. The H1N1 virus remains largely sensitive to the NA inhibitors but is resistant to the matrix protein-2 inhibitors. Extracorporeal membrane oxygenation provides continuous pulmonary (and sometimes cardiac) support and minimizes ventilator-induced lung injury. The potential for life-threatening complications is high. In 2009, in the Conventional Ventilation or ECMO for Severe Adult Respiratory Failure (CESAR) randomized trial of ECMO, the overall survival rate was 63% in the ECMO group compared with 47% in the control group (p = 0.03). Similar studies have been reported from Australia and New Zealand, Canada, and France.

CONCLUSIONS

Supportive management is continued along with ECMO. Antiviral drugs and antimicrobial agents should be given as appropriate, as should nutritional support. Volume management should be used. Ventilator settings should be reduced as ECMO support allows, with a goal of reducing airway pressures, ventilator rate, and FiO(2). Complications of ECMO are common. Bleeding, the most common, can result in death, especially if it occurs intracranially.

Influenza-induced innate immunity: regulators of viral replication, respiratory tract pathology & adaptive immunity

Influenza virus infections usually cause mild to moderately severe respiratory disease, however some infections, like those involving the avian H5N1 virus, can cause massive viral pneumonia, systemic disease and death. The innate immune response of respiratory tract resident cells is the first line of defense and limits virus replication. Enhanced cytokine and chemokine production following infection, however, appears to underlie much of the pathology that develops after infection with highly pathogenic strains. A so-called `cytokine storm' can damage the lung tissue and cause systemic disease, despite the control of viral replication. By summarizing current knowledge of the innate responses mounted to influenza infection, this review highlights the importance of the respiratory tract epithelial cells as regulators of innate and adaptive immunity to influenza virus.

Lessons from the epidemiological surveillance program, during the influenza A (H1N1) virus epidemic, in a reference university hospital of Southeastern Brazil

INTRODUCTION: The case definition of influenza-like illness (ILI) is a powerful epidemiological tool during influenza epidemics. METHODS: A prospective cohort study was conducted to evaluate the impact of two definitions used as epidemiological tools, in adults and children, during the influenza A H1N1 epidemic. Patients were included if they had upper respiratory samples tested for influenza by real-time reverse transcriptase polymerase chain reaction during two periods, using the ILI definition (coughing + temperature ≤ 38ºC) in period 1, and the definition of severe acute respiratory infection (ARS) (coughing + temperature ≤ 38ºC and dyspnoea) in period 2. RESULTS: The study included 366 adults and 147 children, covering 243 cases of ILI and 270 cases of ARS. Laboratory confirmed cases of influenza were higher in adults (50%) than in children (21.6%) ( p < 0.0001) and influenza infection was more prevalent in the ILI definition (53%) than ARS (24.4%) (p < 0.0001). Adults reported more chills and myalgia than children (p = 0.0001). Oseltamivir was administered in 58% and 46% of adults and children with influenza A H1N1, respectively. The influenza A H1N1 case fatality rate was 7% in adults and 8.3% in children. The mean time from onset of illness until antiviral administration was 4 days. CONCLUSIONS: The modification of ILI to ARS definition resulted in less accuracy in influenza diagnosis and did not improve the appropriate time and use of antiviral medication.

Ocular tropism of influenza A viruses: identification of H7 subtype-specific host responses in human respiratory and ocular cells

Highly pathogenic avian influenza (HPAI) H7 virus infection in humans frequently results in conjunctivitis as a major symptom. However, our understanding of what properties govern virus subtype-specific tropism, and of the host responses responsible for eliciting ocular inflammation and pathogenicity following influenza virus infection, are not well understood. To study virus-host interactions in ocular tissue, we infected primary human corneal and conjunctival epithelial cells with H7, H5, and H1 subtype viruses. We found that numerous virus subtypes were capable of infecting and replicating in multiple human ocular cell types, with the highest titers observed with highly pathogenic H7N7 and H5N1 viruses. Similar patterns of proinflammatory cytokine and chemokine production following influenza virus infection were observed in ocular and respiratory cells. However, primary ocular cells infected with HPAI H7N7 viruses were found to have elevated levels of interleukin-1β (IL-1β), a cytokine previously implicated in ocular disease pathology. Furthermore, H7N7 virus infection of corneal epithelial cells resulted in enhanced and significant increases in the expression of genes related to NF-κB signal transduction compared with that after H5N1 or H1N1 virus infection. The differential induction of cytokines and signaling pathways in human ocular cells following H7 virus infection marks the first association of H7 subtype-specific host responses with ocular tropism and pathogenicity. In particular, heightened expression of genes related to NF-κB-mediated signaling transduction following HPAI H7N7 virus infection in primary corneal epithelial cells, but not respiratory cells, identifies activation of a signaling pathway that correlates with the ocular tropism of influenza viruses within this subtype.

Clinical, laboratory and radiologic characteristics of 2009 pandemic influenza A/H1N1 pneumonia: primary influenza pneumonia versus concomitant/secondary bacterial pneumonia

Please cite this paper as: Song et al. (2011). Clinical, laboratory and radiologic characteristics of 2009 pandemic influenza A/H1N1 pneumonia: primary influenza pneumonia versus concomitant/secondary bacterial pneumonia. Influenza and Other Respiratory Viruses 5(6), e535–e543.

Background  Although influenza virus usually involves the upper respiratory tract, pneumonia was seen more frequently with the 2009 pandemic influenza A/H1N1 than with seasonal influenza.

Methods  From September 1, 2009, to January 31, 2010, a specialized clinic for patients (aged ≥15 years) with ILI was operated in Korea University Guro Hospital. RT‐PCR assay was performed to diagnose 2009 pandemic influenza A/H1N1. A retrospective case–case–control study was performed to determine the predictive factors for influenza pneumonia and to discriminate concomitant/secondary bacterial pneumonia from primary influenza pneumonia during the 2009–2010 pandemic.

Results  During the study period, the proportions of fatal cases and pneumonia development were 0·12% and 1·59%, respectively. Patients with pneumonic influenza were less likely to have nasal symptoms and extra‐pulmonary symptoms (myalgia, headache, and diarrhea) compared to patients with non‐pneumonic influenza. Crackle was audible in just about half of the patients with pneumonic influenza (38·5% of patients with primary influenza pneumonia and 53·3% of patients with concomitant/secondary bacterial pneumonia). Procalcitonin, C‐reactive protein (CRP), and lactate dehydrogenase were markedly increased in patients with influenza pneumonia. Furthermore, procalcitonin (cutoff value 0·35 ng/ml, sensitivity 81·8%, and specificity 66·7%) and CRP (cutoff value 86·5 mg/IU, sensitivity 81·8%, and specificity 59·3%) were discriminative between patients with concomitant/secondary bacterial pneumonia and patients with primary influenza pneumonia.

Conclusions  Considering the subtle manifestations of 2009 pandemic influenza A/H1N1 pneumonia in the early stage, high clinical suspicion is required to detect this condition. Both procalcitonin and CRP would be helpful to differentiate primary influenza pneumonia from concomitant/secondary bacterial pneumonia.

Viral replication and innate host responses in primary human alveolar epithelial cells and alveolar macrophages infected with influenza H5N1 and H1N1 viruses

Highly pathogenic influenza H5N1 virus continues to pose a threat to public health. Although the mechanisms underlying the pathogenesis of the H5N1 virus have not been fully defined, it has been suggested that cytokine dysregulation plays an important role. As the human respiratory epithelium is the primary target cell for influenza viruses, elucidating the viral tropism and innate immune responses of influenza H5N1 virus in the alveolar epithelium may help us to understand the pathogenesis of the severe pneumonia associated with H5N1 disease. Here we used primary cultures of differentiated human alveolar type II cells, alveolar type I-like cells, and alveolar macrophages isolated from the same individual to investigate viral replication competence and host innate immune responses to influenza H5N1 (A/HK/483/97) and H1N1 (A/HK/54/98) virus infection. The viral replication kinetics and cytokine and chemokine responses were compared by quantitative PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA). We demonstrated that influenza H1N1 and H5N1 viruses replicated productively in type II cells and type I-like cells although with different kinetics. The H5N1 virus replicated productively in alveolar macrophages, whereas the H1N1 virus led to an abortive infection. The H5N1 virus was a more potent inducer of proinflammatory cytokines and chemokines than the H1N1 virus in all cell types. However, higher levels of cytokine expression were observed for peripheral blood monocyte-derived macrophages than for alveolar macrophages in response to H5N1 virus infection. Our findings provide important insights into the viral tropisms and host responses of different cell types found in the lung and are relevant to an understanding of the pathogenesis of severe human influenza disease.

The first influenza pandemic of the new millennium

In the spring of 2009, a novel influenza A virus of the H1N1 subtype emerged that transmitted efficiently among humans; by June of 2009, the outbreak reached pandemic status. The pandemic virus possesses six viral RNA segments from so-called triple reassortant swine viruses that emerged in North American pig populations in the late 1990s and two viral RNA segments from Eurasian avian-like swine influenza viruses. Most human infections with the virus have been mild; however, severe and fatal infections occurred among certain risk groups, but also among those without any known risk factors. Here, we summarize the evolutionary, epidemiological, clinical, and molecular findings on the pandemic virus. We also discuss the arsenal of antiviral compounds and vaccines available to prevent and treat infections with the virus.

Pandemic influenza A/H1N1 virus infection in solid organ transplant recipients: a multicenter study

BACKGROUND

The 2009 novel influenza A/H1N1 virus pandemic did not spare solid organ transplant (SOT) recipients. We aimed to describe the behavior of pandemic influenza infection in a group of SOT recipients in Argentina.

METHODS

Data from 10 transplant (Tx) centers were retrospectively collected for SOT that presented with a respiratory illness compatible with pandemic influenza A infection, between May and September 2009. Cases were defined as suspected, probable, or confirmed according to diagnostic method.

RESULTS

Seventy-seven cases were included. No significant differences in presenting symptoms, pulmonary infiltrates, and graft involvement were found among 35 suspected, 19 probable, and 23 confirmed cases. The 33 ambulatory cases had significantly more sore throat and headache when compared with 34 cases admitted to medical ward (MW) and 10 admitted to intensive care unit (ICU), 9 of whom required ventilatory support. MW and ICU cases had significantly more dyspnea, hypoxemia, pulmonary infiltrates, and graft dysfunction. Time from onset of symptoms to first visit and to treatment was significantly longer in MW and ICU cases (P=0.008). Coinfections were found in six cases. Most cases received oseltamivir for 5 to 10 days. Six patients (7.8%) died from viral infection at a median of 15 days from admission. No differences in outcome were seen related to the transplanted organ, the immunosuppressive regimen, time from Tx, or confirmation of diagnosis.

CONCLUSIONS

Mortality is higher in Tx recipients than in the general population. Poor outcome seems to be related to a delay in the beginning of treatment.

Innate immune response to influenza A virus in differentiated human alveolar type II cells

Alveolar Type II (ATII) cells are important targets for seasonal and pandemic influenza. To investigate the influenza-induced innate immune response in those cells, we measured the global gene expression profile of highly differentiated ATII cells infected with the influenza A virus at a multiplicity of infection of 0.5 at 4 hours and 24 hours after inoculation. Infection with influenza stimulated a significant increase in the mRNA concentrations of many host defense-related genes, including pattern/pathogen recognition receptors, IFN, and IFN-induced genes, chemokines, and suppressors of cytokine signaling. We verified these changes by quantitative real-time RT-PCR. At the protein level, we detected a robust virus-induced secretion of the three glutamic acid-leucine-arginine (ELR)-negative chemokines CXCL9, CXCL10, and CXCL11, according to ELISA. The ultraviolet inactivation of virus abolished the chemokine and cytokine response. Viral infection did not appear to alter the differentiation of ATII cells, as measured by cellular mRNA and concentrations of surfactant proteins. However, viral infection significantly reduced the secretion of surfactant protein (SP)-A and SP-D. In addition, influenza A virus triggered a time-dependent activation of phosphatidylinositol 3-kinase signaling in ATII cells. The inhibition of this pathway significantly decreased the release of infectious virus and the chemokine response, but did not alter virus-induced cell death. This study provides insights into influenza-induced innate immunity in differentiated human ATII cells, and demonstrates that the alveolar epithelium is a critical part of the initial innate immune response to influenza.

Characterization of antibodies specific for hemagglutinin and neuraminidase proteins of the 1918 and 2009 pandemic H1N1 viruses

Serologic studies have detected protective immunity against 2009 pandemic H1N1 influenza virus (H1N1-2009) in some people. However, further study of preexisting immunity has been complicated by the complexity of the human immunological background. Here, we immunized mice with HA- and NA-encoding plasmids. The cross-neutralizing activity of the anti-HA antisera and the effect of the anti-NA antisera on viral infectivity were evaluated using H1N1-1918- and 2009-pseudotyped particles (pps) and an H1N1-2009 isolate. Antibodies to H1N1-2009 HA (09HA) neutralized pps harboring 09HA or H1N1-1918 HA (18HA); similarly, antibodies to 18HA neutralized pps harboring 18HA or 09HA. Antibodies to 09HA and 18HA also neutralized the H1N1-2009 virus with high efficiency. Antibodies to H1N1-1918 NA (18NA) or H1N1-2009 NA (09NA) both enhanced the infectivity of pps harboring 09NA and 18NA. Although anti-09NA and -18NA antibodies significantly reduced cytopathic effects in multiple-cycle infection assays, conversely, these antibodies enhanced the infectivity of H1N1-2009 in single-cycle infection assays. Our study demonstrates the existence of cross-protection between antibodies against these two antigenically related virus strains and shows that anti-NA antibodies have a dual effect that requires reexamination of their role in human immunity.

The 2009 pandemic H1N1 and triple-reassortant swine H1N1 influenza viruses replicate efficiently but elicit an attenuated inflammatory response in polarized human bronchial epithelial cells

The pandemic H1N1 virus of 2009 (2009 H1N1) produced a spectrum of disease ranging from mild illness to severe illness and death. Respiratory symptoms were frequently associated with virus infection, with relatively high rate of gastrointestinal symptoms reported. To better understand 2009 H1N1 virus pathogenesis in humans, we studied virus and host responses following infection of two cell types: polarized bronchial and pharyngeal epithelial cells, which exhibit many features of the human airway epithelium, and colon epithelial cells to serve as a human intestinal cell model. Selected 2009 H1N1 viruses were compared to both seasonal H1N1 and triple-reassortant swine H1N1 influenza viruses that have circulated among North American pigs since before the 2009 pandemic. All H1N1 viruses replicated productively in airway cells; however, in contrast to seasonal H1N1 virus infection, infection with the 2009 H1N1 and triple-reassortant swine H1N1 viruses resulted in an attenuated inflammatory response, a weaker interferon response, and reduced cell death. Additionally, the H1N1 viruses of swine origin replicated less efficiently at the temperature of the human proximal airways (33°C). We also observed that the 2009 H1N1 viruses replicated to significantly higher titers than seasonal H1N1 virus in polarized colon epithelial cells. These studies reveal that in comparison to seasonal influenza virus, H1N1 viruses of swine origin poorly activate multiple aspects of the human innate response, which may contribute to the virulence of these viruses. In addition, their less efficient replication at human upper airway temperatures has implications for the understanding of pandemic H1N1 virus adaptation to humans.