Pathogenicity of influenza virus

Ex Vivo Experiments Shed Light on the Innate Immune Response from Influenza Virus

The innate immune response is recognized as a key driver in controlling an influenza virus infection in a host. However, the mechanistic action of such innate response is not fully understood. Infection experiments on ex vivo explants from swine trachea represent an efficient alternative to animal experiments, as the explants conserved key characteristics of an organ from an animal. In the present work we compare three cellular automata models of influenza virus dynamics. The models are fitted to free virus and infected cells data from ex vivo swine trachea experiments. Our findings suggest that the presence of an immune response is necessary to explain the observed dynamics in ex vivo organ culture. Moreover, such immune response should include a refractory state for epithelial cells, and not just a reduced infection rate. Our results may shed light on how the immune system responds to an infection event.

Glycocalyx degradation and the endotheliopathy of viral infection

The endothelial glycocalyx (EGX) contributes to the permeability barrier of vessels and regulates the coagulation cascade. EGX damage, which occurs in numerous disease states, including sepsis and trauma, results in endotheliopathy. While influenza and other viral infections are known to cause endothelial dysfunction, their effect on the EGX has not been described. We hypothesized that the H1N1 influenza virus would cause EGX degradation. Human umbilical vein endothelial cells (HUVECs) were exposed to varying multiplicities of infection (MOI) of the H1N1 strain of influenza virus for 24 hours. A dose-dependent effect was examined by using an MOI of 5 (n = 541), 15 (n = 714), 30 (n = 596), and 60 (n = 653) and compared to a control (n = 607). Cells were fixed and stained with FITC-labelled wheat germ agglutinin to quantify EGX. There was no difference in EGX intensity after exposure to H1N1 at an MOI of 5 compared to control (6.20 vs. 6.56 Arbitrary Units (AU), p = 0.50). EGX intensity was decreased at an MOI of 15 compared to control (5.36 vs. 6.56 AU, p<0.001). The degree of EGX degradation was worse at higher doses of the H1N1 virus; however, the decrease in EGX intensity was maximized at an MOI of 30. Injury at MOI of 60 was not worse than MOI of 30. (4.17 vs. 4.47 AU, p = 0.13). The H1N1 virus induces endothelial dysfunction by causing EGX degradation in a dose-dependent fashion. Further studies are needed to characterize the role of this EGX damage in causing clinically significant lung injury during acute viral infection.

Anti-varicella zoster virus and related anti-inflammation effects of ethanolic extract of Elaeocarpus sylvestris

ETHNOPHARMACOLOGICAL RELEVANCE

Elaeocarpus sylvestris var. ellipticus (ES), a plant that grows in Taiwan, Japan, and Jeju Island in Korea. ES root bark, known as "sanduyoung," has long been used in traditional oriental medicine. ES is also traditionally used to treat anxiety, asthma, arthritis, stress, depression, palpitation, nerve pain, epilepsy, migraine, hypertension, liver diseases, diabetes, and malaria. However, lack of efficacy and mechanism studies on ES.

AIM OF THE STUDY

In the present study, we aim to investigate the VZV-antiviral efficacy, pain suppression, and the anti-inflammatory and antipyretic effects of ES.

METHODS

and methods: Inhibition of VZV was evaluated by hollow fiber assays. Analgesic and antipyretic experiments were conducted using ICR mice and SD Rats, and anti-inflammatory experiments were conducted using Raw264.7 cells.

RESULTS

To evaluate the efficacy of ESE against VZV, we conducted antiviral tests. ESE inhibited cell death by disrupting virus and gene expression related to invasion and replication. In addition, ESE suppressed the pain response as measured by writhing and formalin tests and suppressed LPS-induced inflammatory fever. Further, ESE inhibited the phosphorylation of IκB and NF-κB in LPS-induced Raw264.7 cells and expression of COX-2, iNOS, IL-1β, IL-6, and TNF-α.

CONCLUSION

E. sylvestris shows potential as a source of medicine. ESE had a direct effect on VZV and an inhibitory effect on the pain and inflammation caused by VZV infection.

Susceptibilities of human ACE2 genetic variants in coronavirus infection

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in more than 235 million cases worldwide and 4.8 million deaths (October 2021), with various incidences and mortalities among regions/ethnicities. The coronaviruses SARS-CoV, SARS-CoV-2, and HCoV-NL63 utilize the angiotensin-converting enzyme 2 (ACE2) as the receptor to enter cells. We hypothesized that the genetic variability in ACE2 may contribute to the variable clinical outcomes of COVID-19. To test this hypothesis, we first conducted an in silico investigation of single-nucleotide polymorphisms (SNPs) in the coding region of ACE2. We then applied an integrated approach of genetics, biochemistry, and virology to explore the capacity of select ACE2 variants to bind coronavirus spike proteins and mediate viral entry. We identified the ACE2 D355N variant that restricts the spike protein-ACE2 interaction and consequently limits infection both in vitro and in vivo. In conclusion, ACE2 polymorphisms could modulate susceptibility to SARS-CoV-2, which may lead to variable disease severity.

IMPORTANCE There is considerable variation in disease severity among patients infected with SARS-CoV-2, the virus that causes COVID-19. Human genetic variation can affect disease outcome, and the coronaviruses SARS-CoV, SARS-CoV-2, and HCoV-NL63 utilize human ACE2 as the receptor to enter cells. We found that several missense ACE2 single-nucleotide variants (SNVs) that showed significantly altered binding with the spike proteins of SARS-CoV, SARS-CoV-2, and NL63-HCoV. We identified an ACE2 SNP, D355N, that restricts the spike protein-ACE2 interaction and consequently has the potential to protect individuals against SARS-CoV-2 infection. Our study highlights that ACE2 polymorphisms could impact human susceptibility to SARS-CoV-2, which may contribute to ethnic and geographical differences in SARS-CoV-2 spread and pathogenicity.

A New Natural Defense Against Airborne Pathogens

We propose the nasal administration of calcium-enriched physiological salts as a new hygienic intervention with possible therapeutic application as a response to the rapid and tenacious spread of COVID-19. We test the effectiveness of these salts against viral and bacterial pathogens in animals and humans. We find that aerosol administration of these salts to the airways diminishes the exhalation of the small particles that face masks fail to filter and, in the case of an influenza swine model, completely block airborne transmission of disease. In a study of 10 human volunteers (5 less than 65 years and 5 older than 65 years), we show that delivery of a nasal saline comprising calcium and sodium salts quickly (within 15 min) and durably (up to at least 6 h) diminishes exhaled particles from the human airways. Being predominantly smaller than 1 μm, these particles are below the size effectively filtered by conventional masks. The suppression of exhaled droplets by the nasal delivery of calcium-rich saline with aerosol droplet size of around 10 μm suggests the upper airways as a primary source of bioaerosol generation. The suppression effect is especially pronounced (99%) among those who exhale large numbers of particles. In our study, we found this high-particle exhalation group to correlate with advanced age. We argue for a new hygienic practice of nasal cleansing by a calcium-rich saline aerosol, to complement the washing of hands with ordinary soap, use of a face mask, and social distancing.

Synergistic PA and HA mutations confer mouse adaptation of a contemporary A/H3N2 influenza virus

The mouse is the most widely used animal model for influenza virus research. However, the susceptibility of mice to seasonal influenza virus depends on the strain of mouse and on the strain of the influenza virus. Seasonal A/H3N2 influenza viruses do not replicate well in mice and therefore they need to be adapted to this animal model. In this study, we generated a mouse-adapted A/H3N2 virus (A/Switzerland/9715293/2013 [MA-H3N2]) by serial passaging in mouse lungs that exhibited greater virulence compared to the wild-type virus (P0-H3N2). Seven mutations were found in the genome of MA-H3N2: PA(K615E), NP(G384R), NA(G320E) and HA(N122D, N144E, N246K, and A304T). Using reverse genetics, two synergistically acting genes were found as determinants of the pathogenicity in mice. First, the HA substitutions were shown to enhanced viral replication in vitro and, second, the PA-K615E substitution increased polymerase activity, although did not alter virus replication in vitro or in mice. Notably, single mutations had only limited effects on virulence in vitro. In conclusion, a co-contribution of HA and PA mutations resulted in a lethal mouse model of seasonal A/H3N2 virus. Such adapted virus is an excellent tool for evaluation of novel drugs or vaccines and for study of influenza pathogenesis.

Non-lytic clearance of influenza B virus from infected cells preserves epithelial barrier function

Influenza B virus (IBV) is an acute, respiratory RNA virus that has been assumed to induce the eventual death of all infected cells. We and others have shown however, that infection with apparently cytopathic viruses does not necessarily lead to cell death; some cells can intrinsically clear the virus and persist in the host long-term. To determine if any cells can survive direct IBV infection, we here generate a recombinant IBV capable of activating a host-cell reporter to permanently label all infected cells. Using this system, we demonstrate that IBV infection leads to the formation of a survivor cell population in the proximal airways that are ciliated-like, but transcriptionally and phenotypically distinct from both actively infected and bystander ciliated cells. We also show that survivor cells are critical to maintain respiratory barrier function. These results highlight a host response pathway that preserves the epithelium to limit the severity of IBV disease.

Infection of a cell with influenza B virus (IBV) often results in cell death and the role of surviving cells in pathogenesis is unclear. Here, Dumm et al. generate a recombinant IBV that activates a host-cell reporter to permanently label infected cells, and show that surviving cells are important to preserve epithelial barrier function.

Optimization of cell-laden bioinks for 3D bioprinting and efficient infection with influenza A virus

Bioprinting is a new technology, which arranges cells with high spatial resolution, but its potential to create models for viral infection studies has not yet been fully realized. The present study describes the optimization of a bioink composition for extrusion printing. The bioinks were biophysically characterized by rheological and electron micrographic measurements. Hydrogels consisting of alginate, gelatin and Matrigel were used to provide a scaffold for a 3D arrangement of human alveolar A549 cells. A blend containing 20% Matrigel provided the optimal conditions for spatial distribution and viability of the printed cells. Infection of the 3D model with a seasonal influenza A strain resulted in widespread distribution of the virus and a clustered infection pattern that is also observed in the natural lung but not in two-dimensional (2D) cell culture, which demonstrates the advantage of 3D printed constructs over conventional culture conditions. The bioink supported viral replication and proinflammatory interferon release of the infected cells. We consider our strategy to be paradigmatic for the generation of humanized 3D tissue models by bioprinting to study infections and develop new antiviral strategies.

Influenza Virus Infection of Human Lymphocytes Occurs in the Immune Cell Cluster of the Developing Antiviral Response

Monocytes-macrophages and lymphocytes are recruited to the respiratory tract in response to influenza virus challenge and are exposed to the virus during the establishment of immune defenses. The susceptibility of human lymphocytes to infection was assessed. The presence of monocytes-macrophages was required to attain infection of both resting and proliferating lymphocytes. Lymphocyte infection occurred in the context of immune cell clusters and was blocked by the addition of anti-intercellular adhesion molecule-1 (ICAM-1) antibody to prevent cell clustering. Both peripheral blood-derived and bronchoalveolar lymphocytes were susceptible to infection. Both CD4⁺ and CD8⁺ T lymphocytes were susceptible to influenza virus infection, and the infected CD4⁺ and CD8⁺ lymphocytes served as infectious foci for other nonpermissive or even virus-permissive cells. These data show that monocytes-macrophages and both CD4⁺ and CD8⁺ lymphocytes can become infected during the course of an immune response to influenza virus challenge. The described leukocyte interactions during infection may play an important role in the development of effective anti-influenza responses.

In vivo imaging of the pathophysiological changes and neutrophil dynamics in influenza virus-infected mouse lungs

The pathophysiological changes that occur in lungs infected with influenza viruses are poorly understood. Here we established an in vivo imaging system that combines two-photon excitation microscopy and fluorescent influenza viruses of different pathogenicity. This approach allowed us to monitor and correlate several parameters and physiological changes including the spread of infection, pulmonary permeability, pulmonary perfusion speed, number of recruited neutrophils in infected lungs, and neutrophil motion in the lungs of live mice. Several physiological changes were larger and occurred earlier in mice infected with a highly pathogenic H5N1 influenza virus compared with those infected with a mouse-adapted human strain. These findings demonstrate the potential of our in vivo imaging system to provide novel information about the pathophysiological consequences of virus infections.

In Vivo Infection Model of Severe Influenza A Virus

The lung is constantly exposed to both environmental and microbial challenge. As a "contained" organ, it also constitutes an excellent "self-contained" tissue to examine inflammatory responses and cellular infiltration into a diseased organ. Influenza A virus (IAV) causes both mild and severe inflammation that is strain specific following infection of the lung epithelium that spreads to other cells of the lung environment. Here, we describe a method of intranasal inoculation of the lung with IAV that can be used as a preclinical model of infection. Mice can be monitored for clinical signs of infection and tissue and lung fluid collected for further analysis to dissect the immunological consequences of IAV infection. Importantly, this method can be modified to introduce other pathogens, therapies and environmental stimuli to examine immune responses in the lung.

Influenza A Virus and Influenza B Virus Can Induce Apoptosis via Intrinsic or Extrinsic Pathways and Also via NF-κB in a Time and Dose Dependent Manner

Influenza viruses are able to cause annual epidemics and pandemics due to their mutation rates and reassortment capabilities leading to antigenic shifts and drifts. To identify host response to influenza A and B viruses on A549 and MDCK II cells at low and high MOIs, expressions of MxA and caspases 3, 8, and 9 and BAD, TNFα, and IκBα genes were measured in the cells supernatants. H1N1 and H3N2 prefer to initially enhance the intrinsic pathway, determined by higher caspase 9 activity in MDCK II cells compared to caspase 8 activity and vice versa in A549 cells at different MOIs, while INF B prefers extrinsic pathway in A549 cells according to significant low or undetectable caspase 9 activity and high activity of caspase 8 but also can induce intrinsic pathway in MDCK II cells as determined by significant low or undetectable activity of caspase 8 and high caspase 9 activity at different MOIs; the considerable MxA expression was found in influenza A and B viruses infected A549 and MDCK II cells at low MOIs. In conclusion, influenza A and B viruses induced extrinsic and intrinsic apoptosis in parallel, and the induction was associated with viral infection in a dose dependent manner.

Identifying the Critical Domain of LL-37 Involved in Mediating Neutrophil Activation in the Presence of Influenza Virus: Functional and Structural Analysis

The human cathelicidin LL-37 has been shown to play a role in host defense against influenza A viruses (IAV) through direct antiviral effects and through modulating inflammatory responses to infection. We recently showed that LL-37 increases neutrophil respiratory burst and neutrophil extracellular trap (NET) responses to IAV through engaging formyl peptide receptor 2 (FPR-2). In this paper we show that a fragment of LL-37, GI-20, which is composed of the central helical segment of the peptide, has similar effects as LL-37 on neutrophil activation. In addition to increasing respiratory burst and NET responses of the cells to IAV through an FPR-2 dependent mechanism, it reduces neutrophil IL-8 production to IAV (also like LL-37). The N-terminal fragment, LL-23, did not have similar effects. Both GI-20 and LL-37 increase neutrophil intracellular calcium levels and their ability to increase neutrophil activation responses was calcium dependent and partially inhibited by pertussis toxin. These studies show that the central helix of LL-37 retains the ability of LL-37 to modulate neutrophil responses through FPR-2. Based on our findings we developed a homology model of FPR-2 and performed docking experiments of LL-37 and GI-20 with the receptor.

Serum amyloid P is a sialylated glycoprotein inhibitor of influenza A viruses

Members of the pentraxin family, including PTX3 and serum amyloid P component (SAP), have been reported to play a role in innate host defence against a range of microbial pathogens, yet little is known regarding their antiviral activities. In this study, we demonstrate that human SAP binds to human influenza A virus (IAV) strains and mediates a range of antiviral activities, including inhibition of IAV-induced hemagglutination (HA), neutralization of virus infectivity and inhibition of the enzymatic activity of the viral neuraminidase (NA). Characterization of the anti-IAV activity of SAP after periodate or bacterial sialidase treatment demonstrated that α(2,6)-linked sialic acid residues on the glycosidic moiety of SAP are critical for recognition by the HA of susceptible IAV strains. Other proteins of the innate immune system, namely human surfactant protein A and porcine surfactant protein D, have been reported to express sialylated glycans which facilitate inhibition of particular IAV strains, yet the specific viral determinants for recognition of these inhibitors have not been defined. Herein, we have selected virus mutants in the presence of human SAP and identified specific residues in the receptor-binding pocket of the viral HA which are critical for recognition and therefore susceptibility to the antiviral activities of SAP. Given the widespread expression of α(2,6)-linked sialic acid in the human respiratory tract, we propose that SAP may act as an effective receptor mimic to limit IAV infection of airway epithelial cells.

Respiratory infection of mice with mammalian reoviruses causes systemic infection with age and strain dependent pneumonia and encephalitis

BACKGROUND

Because mammalian reoviruses are isolated from the respiratory tract we modeled the natural history of respiratory infection of adult and suckling mice with T1 Lang (T1L) and T3 Dearing (T3D) reoviruses.

METHODS

Adult and suckling Balb/c mice were infected by the intranasal route and were assessed for dose response of disease as well as viral replication in the lung and other organs. Viral antigen was assessed by immunofluorescence and HRP staining of tissue sections and histopathology was assessed on formalin fixed, H + E stained tissue sections.

RESULTS

Intranasal infection of adult mice resulted in fatal respiratory distress for high doses (10(7) pfu) of T1L but not T3D. In contrast both T1L and T3D killed suckling mice at moderate viral dosages (10(5) pfu) but differed in clinical symptoms where T1L induced respiratory failure and T3D caused encephalitis. Infections caused transient viremia that resulted in spread to peripheral tissues where disease correlated with virus replication, and pathology. Immunofluorescent staining of viral antigens in the lung showed reovirus infection was primarily associated with alveoli with lesser involvement of bronchiolar epithelium. Immunofluorescent and HRP staining of viral antigens in brain showed infection of neurons by T3D and glial cells by T1L.

CONCLUSIONS

These mouse models of reovirus respiratory infection demonstrated age and strain dependent disease that are expected to be relevant to understanding and modulating natural and therapeutic reovirus infections in humans.

Cloned defective interfering influenza virus protects ferrets from pandemic 2009 influenza A virus and allows protective immunity to be established

Influenza A viruses are a major cause of morbidity and mortality in the human population, causing epidemics in the winter, and occasional worldwide pandemics. In addition there are periodic outbreaks in domestic poultry, horses, pigs, dogs, and cats. Infections of domestic birds can be fatal for the birds and their human contacts. Control in man operates through vaccines and antivirals, but both have their limitations. In the search for an alternative treatment we have focussed on defective interfering (DI) influenza A virus. Such a DI virus is superficially indistinguishable from a normal virus but has a large deletion in one of the eight RNAs that make up the viral genome. Antiviral activity resides in the deleted RNA. We have cloned one such highly active DI RNA derived from segment 1 (244 DI virus) and shown earlier that intranasal administration protects mice from lethal disease caused by a number of different influenza A viruses. A more cogent model of human influenza is the ferret. Here we found that intranasal treatment with a single dose of 2 or 0.2 µg 244 RNA delivered as A/PR/8/34 virus particles protected ferrets from disease caused by pandemic virus A/California/04/09 (A/Cal; H1N1). Specifically, 244 DI virus significantly reduced fever, weight loss, respiratory symptoms, and infectious load. 244 DI RNA, the active principle, was amplified in nasal washes following infection with A/Cal, consistent with its amelioration of clinical disease. Animals that were treated with 244 DI RNA cleared infectious and DI viruses without delay. Despite the attenuation of infection and disease by DI virus, ferrets formed high levels of A/Cal-specific serum haemagglutination-inhibiting antibodies and were solidly immune to rechallenge with A/Cal. Together with earlier data from mouse studies, we conclude that 244 DI virus is a highly effective antiviral with activity potentially against all influenza A subtypes.

Resolution of immune response by recombinant transforming growth factor-beta (rTGF-β) during influenza A virus infection

BACKGROUND & OBJECTIVES

Replication of influenza A virus in the respiratory tract leads to cell damage and liberation of cytokines and chemokines. The in vivo cytokine induction and modulation by recombinant transforming growth factor- β1 (rTGF-β1) has not been studied. Therefore, in the present study the effect of rTGF-β1, a potent immunomodulatory cytokine which has anti-inflammatory properties and downregulates the release of inflammatory molecules, against influenza-virus infection in the airway of mice was investigated.

METHODS

rTGF-β1 was administered intravenously to mice with concomitant intranasal infection of influenza A/Udorn/317/72 (H3N2) virus, and the survival rate, virus titre, histopathological changes and levels of factors regulating inflammation in the airway fluid were analysed.

RESULT

The immune response to influenza A virus was characterized by an influx of both macrophages and lymphocytes into the lungs of the infected host. rTGF-β1 significantly suppressed virus multiplication and improved the survival rate of mice. rTGF-β1 downregulated infiltration of neutrophils and the release of inflammatory molecules, such as interferon-gamma (IFN-γ), interleukin-1 β (IL-1β) and stimulated release of IL-10 that potentiates anti-inflammatory response into airway.

INTERPRETATION & CONCLUSIONS

A generalized pulmonary inflammation does not contribute to viral clearance but represents an immunological background within which antiviral immunity operates. Treatment with rTGF-β1 reduced macrophage count and neutrophils influx in lungs of infected mice.

Influenza virus neuraminidase contributes to the dextran sulfate-dependent suppressive replication of some influenza A virus strains

Dextran sulfate (DS), a negatively charged, sulfated polysaccharide, suppresses the replication of an influenza A virus strain, and this suppression is associated with inhibition of the hemagglutinin (HA)-dependent fusion activity. However, it remains unknown whether the replication of all or just some influenza A virus strains is suppressed by DS, or whether HA is the only target for the replication suppression. In the present study, we found that DS inhibited the replication of some, but not all influenza A virus strains. The suppression in the DS-sensitive strains was dose-dependent and neutralized by diethylaminoethyl-dextran (DD), which has a positive charge. The suppression by DS was observed not only at the initial stage of viral infection, which includes viral attachment and entry, but also at the late stage, which includes virus assembly and release from infected cells. Electron microscopy revealed that the DS induced viral aggregation at the cell surface. The neuraminidase (NA) activity of the strains whose viral replication was inhibited at the late stage was also more suppressed by DS than that of the strains whose replication was not inhibited, and this inhibition of NA activity was also neutralized by adding positively charged DD. Furthermore, we found that replacing the NA gene of a strain in which viral replication was inhibited by DS at the late stage with the NA gene from a strain in which viral replication was not inhibited, eliminated the DS-dependent suppression. These results suggest that the influenza virus NA contributes to the DS-suppressible virus release from infected cells at the late stage, and the suppression may involve the inhibition of NA activity by DS's negative charge.

Mouse-adapted H9N2 influenza A virus PB2 protein M147L and E627K mutations are critical for high virulence

H9N2 influenza viruses have been circulating worldwide in multiple avian species and have repeatedly infected humans to cause typical disease. The continued avian-to-human interspecies transmission of H9N2 viruses raises concerns about the possibility of viral adaption with increased virulence for humans. To investigate the genetic basis of H9N2 influenza virus host range and pathogenicity in mammals, we generated a mouse-adapted H9N2 virus (SD16-MA) that possessed significantly higher virulence than wide-type virus (SD16). Increased virulence was detectable after 8 sequential lung passages in mice. Five amino acid substitutions were found in the genome of SD16-MA compared with SD16 virus: PB2 (M147L, V250G and E627K), HA (L226Q) and M1 (R210K). Assessments of replication in mice showed that all of the SD16-MA PB2, HA and M1 genome segments increased virus replication; however, only the mouse-adapted PB2 significantly increased virulence. Although the PB2 E627K amino acid substitution enhanced viral polymerase activity and replication, none of the single mutations of mouse adapted PB2 could confer increased virulence on the SD16 backbone. The combination of M147L and E627K significantly enhanced viral replication ability and virulence in mice. Thus, our results show that the combination of PB2 amino acids at position 147 and 627 is critical for the increased pathogenicity of H9N2 influenza virus in mammalian host.

Adaption of seasonal H1N1 influenza virus in mice

The experimental infection of a mouse lung with influenza A virus has proven to be an invaluable model for studying the mechanisms of viral adaptation and virulence. The mouse adaption of human influenza A virus can result in mutations in the HA and other proteins, which is associated with increased virulence in mouse lungs. In this study, a mouse-adapted seasonal H1N1 virus was obtained through serial lung-to-lung passages and had significantly increased virulence and pathogenicity in mice. Genetic analysis indicated that the increased virulence of the mouse-adapted virus was attributed to incremental acquisition of three mutations in the HA protein (T89I, N125T, and D221G). However, the mouse adaption of influenza A virus did not change the specificity and affinity of receptor binding and the pH-dependent membrane fusion of HA, as well as the in vitro replication in MDCK cells. Notably, infection with the mouse adapted virus induced severe lymphopenia and modulated cytokine and chemokine responses in mice. Apparently, mouse adaption of human influenza A virus may change the ability to replicate in mouse lungs, which induces strong immune responses and inflammation in mice. Therefore, our findings may provide new insights into understanding the mechanisms underlying the mouse adaption and pathogenicity of highly virulent influenza viruses.

Intranasal immunization of ferrets with commercial trivalent influenza vaccines formulated in a nanoemulsion-based adjuvant

NB-1008 is a surfactant-stabilized soybean oil-in-water nanoemulsion (NE) adjuvant with influenza virus antigen incorporated into the NE by simple mixing. Intranasal administration of the antigen with NE adjuvant efficiently produces both mucosal and serum antibody responses as well as a robust cellular Th1 immune response. To demonstrate the adjuvant effect of the W(80)5EC NE, a killed commercial influenza vaccine for intramuscular administration (Fluzone or Fluvirin) was mixed with the W(80)5EC NE adjuvant and administered intranasally to naïve ferrets. After a single intranasal immunization, the adjuvanted influenza vaccine elicited elevated serum hemagglutination inhibition (HAI) geometric mean titers (GMTs) ranging from 196 to 905 for the three hemagglutinin (HA) antigens present in the vaccine, which are approximately 19- to 90-fold higher titers at 1/50 the standard intramuscular commercial nonadjuvanted influenza vaccine dose. Seroconversion rates of 67% to 100% were achieved against each of the three viral strains present. The adjuvanted nasal influenza vaccine also produced significant cross immunity to five other H3N2 influenza virus strains not present in the vaccine and produced sterile immunity after challenge with homologous live virus. No safety issues were observed in 249 ferrets receiving the adjuvanted influenza vaccine. These findings demonstrate the ability of W(80)5EC NE to adjuvant nasally administered influenza vaccine and provide a basis for studying the intranasal W(80)5EC-adjuvanted influenza vaccine in humans.

Receptor specificity of the influenza virus hemagglutinin modulates sensitivity to soluble collectins of the innate immune system and virulence in mice

The hemagglutinin (HA) glycoprotein of influenza virus binds to cell surface sialic acid (SA) to initiate infection. In this study, a mutant of influenza A virus strain BJx109 (H3N2) was plaque-purified from the lungs of virus-infected mice that had been depleted of airway macrophages. Sequence analysis identified a single amino acid substitution (S186I) in the vicinity of the receptor-binding site of HA. This substitution was associated with enhanced binding to α(2,3)-Gal-linked SA and an increased ability to infect murine airway epithelial cells. Mutant viruses were less sensitive to neutralization by mouse airway fluids and less efficient in their ability to infect murine macrophages. Moreover, infection of mice with viruses bearing the S186I substitution led to severe disease, characterized by enhanced virus replication, lung pathology and pulmonary edema. Together, these studies confirm that residue 186 of H3 subtype viruses is a critical determinant of virulence in a mouse model of influenza infection.

The role of neutrophils during mild and severe influenza virus infections of mice

Neutrophils have been implicated in both protective and pathological responses following influenza virus infections. We have used mAb 1A8 (anti-Ly6G) to specifically deplete LyG6(high) neutrophils and induce neutropenia in mice infected with virus strains known to differ in virulence. Mice were also treated with mAb RB6-8C5 (anti-Ly6C/G or anti-Gr-1), a mAb widely used to investigate the role of neutrophils in mice that has been shown to bind and deplete additional leukocyte subsets. Using mAb 1A8, we confirm the beneficial role of neutrophils in mice infected with virus strains of intermediate (HKx31; H3N2) or high (PR8; H1N1) virulence whereas treatment of mice infected with an avirulent strain (BJx109; H3N2) did not affect disease or virus replication. Treatment of BJx109-infected mice with mAb RB6-8C5 was, however, associated with significant weight loss and enhanced virus replication indicating that other Gr-1(+) cells, not neutrophils, limit disease severity during mild influenza infections.

A review of mathematical models of influenza A infections within a host or cell culture: lessons learned and challenges ahead

Most mathematical models used to study the dynamics of influenza A have thus far focused on the between-host population level, with the aim to inform public health decisions regarding issues such as drug and social distancing intervention strategies, antiviral stockpiling or vaccine distribution. Here, we investigate mathematical modeling of influenza infection spread at a different scale; namely that occurring within an individual host or a cell culture. We review the models that have been developed in the last decades and discuss their contributions to our understanding of the dynamics of influenza infections. We review kinetic parameters (e.g., viral clearance rate, lifespan of infected cells) and values obtained through fitting mathematical models, and contrast them with values obtained directly from experiments. We explore the symbiotic role of mathematical models and experimental assays in improving our quantitative understanding of influenza infection dynamics. We also discuss the challenges in developing better, more comprehensive models for the course of influenza infections within a host or cell culture. Finally, we explain the contributions of such modeling efforts to important public health issues, and suggest future modeling studies that can help to address additional questions relevant to public health.

Detection of influenza virus induced ultrastructural changes and DNA damage

The influenza virus generally causes damage to epithelial cells of respiratory tract and infection of cells with this virus often results in cell death with apoptotic characteristics. Reports are available implicating influenza virus as a causative agent of chromosomal aberrations in cells and culture. The objective of this study was to analyze the process of cell death caused by influenza virus (A/Udorn/317/72, H3N2) infection in cultured HeLa cells by electron microscopy and comet assay. The apoptotic study was performed using light microscopy electron microscopy and comet assay to observe the changes in cell morphology and DNA fragmentation. HeLa cells, infected with influenza virus were harvested at various time periods to observe the ultrastructural changes. This infection gave rise to nuclear fragmentation and chromatin condensation accompanied by chromosomal DNA fragmentation into oligonucleosomes. The pattern of comet assay revealed that the apoptosis occurred due to fragmentation of the DNA of the cells which reached the maximum level at 36 h post infection. Ultrastructural study showed extensive chromatin condensation and nuclear fragmentation which are the characteristic features of apoptosis.

Adaptation of pandemic H1N1 influenza viruses in mice

The molecular mechanism by which pandemic 2009 influenza A viruses were able to sufficiently adapt to humans is largely unknown. Subsequent human infections with novel H1N1 influenza viruses prompted an investigation of the molecular determinants of the host range and pathogenicity of pandemic influenza viruses in mammals. To address this problem, we assessed the genetic basis for increased virulence of A/CA/04/09 (H1N1) and A/TN/1-560/09 (H1N1) isolates, which are not lethal for mice, in a new mammalian host by promoting their mouse adaptation. The resulting mouse lung-adapted variants showed significantly enhanced growth characteristics in eggs, extended extrapulmonary tissue tropism, and pathogenicity in mice. All mouse-adapted viruses except A/TN/1-560/09-MA2 grew faster and to higher titers in cells than the original strains. We found that 10 amino acid changes in the ribonucleoprotein (RNP) complex (PB2 E158G/A, PA L295P, NP D101G, and NP H289Y) and hemagglutinin (HA) glycoprotein (K119N, G155E, S183P, R221K, and D222G) controlled enhanced mouse virulence of pandemic isolates. HA mutations acquired during adaptation affected viral receptor specificity by enhancing binding to alpha2,3 together with decreasing binding to alpha2,6 sialyl receptors. PB2 E158G/A and PA L295P amino acid substitutions were responsible for the significant enhancement of transcription and replication activity of the mouse-adapted H1N1 variants. Taken together, our findings suggest that changes optimizing receptor specificity and interaction of viral polymerase components with host cellular factors are the major mechanisms that contribute to the optimal competitive advantage of pandemic influenza viruses in mice. These modulators of virulence, therefore, may have been the driving components of early evolution, which paved the way for novel 2009 viruses in mammals.

Antimicrobial resistance of bacterial agents of the upper respiratory tract in South Indian population

The study was aimed at determining bacterial agents of the upper respiratory tract and the susceptibility patterns of isolates to antibiotics. The throat swab samples from 250 patients suspected of upper respiratory tract infection (URTI) were obtained from the General Medicine outpatient department of a Rural Health Centre of Rajah Muthiah Medical College and Hospital (RMMC and H), Annamalai University, Chidambaram, Tamilnadu, India and inoculated in the culture medium. The bacterial infection was confirmed only in 228 patients. The organisms isolated on medium were identified by their cultural, morphological and biochemical characteristics. Staphylocccus aureus was identified as the most prevalent bacterial isolate (45.61%) followed by β hemolytic streptococci (22.51%). Thirty four strains (14.91%) were identified as Klebsiella penumoniae, 19 (8.33%) as Pseudomonas aeruginosa and the rest belonged to a hemolytic streptococci, Escherichia coli and Haemophitus influenzae. All Staphylococcus spp, were resistant to penicillin., ampicillin and co-trimoxazole. All the isolates were resistant to at least one antibiotic. The overall resistance rates were generally low for gentaruicin, cefixine and ceftazidime respectively.

Poly(gamma-glutamic acid) nano-particles combined with mucosal influenza virus hemagglutinin vaccine protects against influenza virus infection in mice

Adding poly(gamma-glutamic acid) nano-particles (gamma-PGA-NPs), a safe, natural material, to subcutaneous immunization with influenza virus hemagglutinin (HA) vaccine increases the protective immune responses against influenza virus in mice. Here, we examined whether intranasal administration of the HA vaccine with gamma-PGA-NPs would induce protection from influenza virus challenge in mice. Intranasal immunization with the mixture of gamma-PGA-NPs and HA vaccine from an influenza virus strain A/PR/8/34 (H1N1) or A/New Caledonia/20/99 (H1N1) enhanced protection of mice from A/PR/8/34 infection. Intranasal immunization with A/New Caledonia/20/99 HA vaccine and gamma-PGA-NPs induced cell-mediated immune responses and neutralizing antibody production for both A/New Caledonia/20/99 and A/PR/8/34. These data suggest that gamma-PGA-NPs may have potential for clinical applications as a mucosal adjuvant.

Receptor for advanced glycation end products is detrimental during influenza A virus pneumonia

Pneumonia caused by influenza A virus (IAV) can have devastating effects, resulting in respiratory failure and death. The idea that a new influenza pandemic might occur in the near future has triggered renewed interests in IAV infection. The receptor for advanced glycation end products (RAGE) is expressed on different cell types and plays a key role in diverse inflammatory processes. We here investigated the role of RAGE in the host response to IAV pneumonia using wild-type (wt) and RAGE deficient ((-/-)) mice. Whereas strong RAGE was constitutively expressed in the lungs of uninfected wt mice, in particular on endothelium, IAV pneumonia was associated with enhanced expression on endothelium and de novo expression on bronchial epithelium. Additionally, the high-affinity RAGE ligand high mobility group box 1 was upregulated during IAV pneumonia. RAGE(-/-) mice were relatively protected from IAV induced mortality and showed an improved viral clearance and enhanced cellular T cell response and activation of neutrophils. These data suggest that RAGE is detrimental during IAV pneumonia.

Influenza virus infection decreases tracheal mucociliary velocity and clearance of Streptococcus pneumoniae

Influenza virus infections increase susceptibility to secondary bacterial infections, such as pneumococcal pneumonia, resulting in increased morbidity and mortality. Influenza-induced tissue damage is hypothesized to increase susceptibility to Streptococcus pneumoniae infection by increasing adherence to the respiratory epithelium. Using a mouse model of influenza infection followed by S. pneumoniae infection, we found that an influenza infection does not increase the number of pneumococci initially present within the trachea, but does inhibit pneumococcal clearance by 2 hours after infection. To determine whether influenza damage increases pneumococcal adherence, we developed a novel murine tracheal explant system to determine influenza-induced tissue damage and subsequent pneumococcal adherence. Murine tracheas were kept viable ex vivo as shown by microscopic examination of ciliary beating and cellular morphology using continuous media flow for up to 8 days. Tracheas were infected with influenza virus for 0.5-5 days ex vivo, and influenza-induced tissue damage and the early stages of repair to the epithelium were assessed histologically. A prior influenza infection did not increase pneumococcal adherence, even when the basement membrane was maximally denuded or during the repopulation of the basement membrane with undifferentiated epithelial cells. We measured mucociliary clearance in vivo and found it was decreased in influenza-infected mice. Together, our results indicate that exposure of the tracheal basement membrane contributes minimally to pneumococcal adherence. Instead, an influenza infection results in decreased tracheal mucociliary velocity and initial clearance of pneumococci, leading to an increased pneumococcal burden as early as 2 hours after pneumococcal infection.

A plant-produced influenza subunit vaccine protects ferrets against virus challenge

Background  Influenza A viruses are of major concern for public health, causing worldwide epidemics associated with high morbidity and mortality. Vaccines are critical for protection against influenza, but given the recent emergence of new strains with pandemic potential, and some limitations of the current production systems, there is a need for new approaches for vaccine development.

Objective  To demonstrate the immunogenicity and protective efficacy of plant‐produced influenza antigens.

Method  We engineered, using influenza A/Wyoming/3/03 (H3N2) as a model virus, the stem and globular domains of hemagglutinin (HA) produced in plants as fusions to a carrier protein and used purified antigens with and without adjuvant for ferret immunization.

Results  These plant‐produced antigens were highly immunogenic and conferred complete protection against infection in the ferret challenge model. The addition of plant‐produced neuraminidase was shown to enhance the immune response in ferrets.

Conclusions  Plants can be used as a production vehicle for vaccine development against influenza. Domains of HA can generate protective immune responses in ferrets.

Viral RNA polymerase complex promotes optimal growth of 1918 virus in the lower respiratory tract of ferrets

The 1918 influenza pandemic was the most devastating outbreak of infectious disease in human history, accounting for about 50 million deaths worldwide. In addition to a significant number of cases of secondary bacterial pneumonia, this highly pathogenic strain of influenza A virus caused fatal primary viral pneumonia. To identify the viral gene(s) chiefly responsible for the high virulence of the 1918 virus, we generated a series of reassortants between the 1918 virus and a contemporary human H1N1 virus (A/Kawasaki/173/2001; K173) using reverse genetics. We then assessed their virulence properties in ferrets, a model closely resembling humans in terms of sensitivity to influenza virus infection and pattern of spread after intranasal inoculation. Substitution of single genes from the 1918 virus in the genetic background of K173 virus did not markedly alter the pattern of infection. That is, the reassortants grew well in nasal turbinates, but only sporadically (if at all) in the trachea and lungs. One exception was the 1918PB1/K173 reassortant, which replicated efficiently in lung tissues as well as the upper respiratory tract. A reassortant virus expressing the 1918 viral RNA polymerase complex (PA, PB1, and PB2) and nucleoprotein showed virulence properties in the upper and lower respiratory tracts of ferrets that closely resembled those of wild-type 1918 virus. Our findings strongly implicate the viral RNA polymerase complex as a major determinant of the pathogenicity of the 1918 pandemic virus. This new insight may aid in identifying virulence factors in future pandemic viruses that could be targeted with antiviral compounds.

Antimicrobial resistance of bacterial agents of the upper respiratory tract of school children in Buea, Cameroon

The study was aimed at determining bacterial agents of the upper respiratory tract and the susceptibility patterns of isolates to antibiotics. In total, 200 throat swabs were obtained from students attending different boarding schools within the Buea Municipality and screened to obtain the prevalence of respiratory pathogens and to understand the antibiotic susceptibility patterns of isolates using standard microbiological procedure and the disc-diffusion test. Of the 200 samples screened, 112 (56%) had positive cultures with the dominant bacterial pathogens being Haemophilus influenzae (20%), followed by Streptococcus pneumoniae (15%), Klebsiella pneumoniae (11%), and Staphylococcus aureus (10%). Although 56% of the isolates were recovered from females compared to 44% from males, the difference was not statistically significant (p>0.05). Sixty-seven percent of the pathogens were isolated from the age-group of 10-13 years, 19.6% from the age-group of 14-17 years, and 12.5% from the age-group of 18-21 years. Antibiotic susceptibility testing revealed that gentamicin (92%) and cefuroxime (88.4%) were the most effective antibiotics against the isolates. Generally, susceptibility ranged from 0% to 92% depending on the antibiotic and the species of microorganism. Penicillin had the highest (100%) resistance to all the isolates. The findings revealed that students living in boarding schools in the Buea Municipality were at risk of acquiring upper respiratory tract infections from their peers since the upper respiratory tract of more than 50% of the students was colonized with respiratory pathogens. Although multidrug-resistant strains of organisms were identified, gentamicin and cefuroxime are recommended as the first-line antibiotics of choice against the pathogens. There is, therefore, a need for surveillance of nasopharyngeal carriage of resistant strains of these organisms, especially H. influenzae in unhealthy school children since the vaccine is yet to be introduced in Cameroon. The findings have clinical and epidemiological significance.

The role of neutrophils in the upper and lower respiratory tract during influenza virus infection of mice

Background

Neutrophils have been shown to play a role in host defence against highly virulent and mouse-adapted strains of influenza virus, however it is not clear if an effective neutrophil response is an important factor moderating disease severity during infection with other virus strains. In this study, we have examined the role of neutrophils during infection of mice with influenza virus strain HKx31, a virus strain of the H3N2 subtype and of moderate virulence for mice, to determine the role of neutrophils in the early phase of infection and in clearance of influenza virus from the respiratory tract during the later phase of infection.

Methods

The anti-Gr-1 monoclonal antibody (mAb) RB6-8C5 was used to (i) identify neutrophils in the upper (nasal tissues) and lower (lung) respiratory tract of uninfected and influenza virus-infected mice, and (ii) deplete neutrophils prior to and during influenza virus infection of mice.

Results

Neutrophils were rapidly recruited to the upper and lower airways following influenza virus infection. We demonstrated that use of mAb RB6-8C5 to deplete C57BL/6 (B6) mice of neutrophils is complicated by the ability of this mAb to bind directly to virus-specific CD8⁺ T cells. Thus, we investigated the role of neutrophils in both the early and later phases of infection using CD8⁺ T cell-deficient B6.TAP^-/- mice. Infection of B6.TAP^-/- mice with a low dose of influenza virus did not induce clinical disease in control animals, however RB6-8C5 treatment led to profound weight loss, severe clinical disease and enhanced virus replication throughout the respiratory tract.

Conclusion

Neutrophils play a critical role in limiting influenza virus replication during the early and later phases of infection. Furthermore, a virus strain of moderate virulence can induce severe clinical disease in the absence of an effective neutrophil response.

Influenza virus protecting RNA: an effective prophylactic and therapeutic antiviral

Another influenza pandemic is inevitable, and new measures to combat this and seasonal influenza are urgently needed. Here we describe a new concept in antivirals based on a defined, naturally occurring defective influenza virus RNA that has the potential to protect against any influenza A virus in any animal host. This "protecting RNA" (244 RNA) is incorporated into virions which, although noninfectious, deliver the RNA to those cells of the respiratory tract that are naturally targeted by infectious influenza virus. A 120-ng intranasal dose of this 244 protecting virus completely protected mice against a simultaneous challenge of 10 50% lethal doses with influenza A/WSN (H1N1) virus. The 244 virus also protected mice against strong challenge doses of all other subtypes tested (i.e., H2N2, H3N2, and H3N8). This prophylactic activity was maintained in the animal for at least 1 week prior to challenge. The 244 virus was 10- to 100-fold more active than previously characterized defective influenza A viruses, and the protecting activity was confirmed to reside in the 244 RNA molecule by recovering a protecting virus entirely from cloned cDNA. There was a clear therapeutic benefit when the 244 virus was administered 24 to 48 h after a lethal challenge, an effect which has not been previously observed with any defective virus. Protecting virus reduced, but did not abolish, replication of challenge virus in mouse lungs during both prophylactic and therapeutic treatments. Protecting virus is a novel antiviral, having the potential to combat human influenza virus infections, particularly when the infecting strain is not known or is resistant to antiviral drugs.

Chapter 7 Orthomyxovirus infections

The earth is a unity for influenza A virus in a manner not yet found for probably any other parasite and epidemics occur in all inhabited parts of the globe regardless of latitude, longitude, altitude, climate, rainfall, temperature, humidity, race and sex. Influenza A is the classic pandemic virus infection of man and influenza B virus also can cause sharp outbreaks, resulting in significant mortality. An overwhelming amount of data has accumulated on the biochemistry, cell biology, and epidemiology of influenza, but prospects of control of epidemics in the near future are dim. Meanwhile, a holding operation can be achieved using inactivated vaccine and rimantadine (100 mg/daily) in special risk groups in the population until new more effective vaccines and broad spectrum antivirals (active against influenza A and B virus) are developed. Research work is centered on biotechnology to produce immunogenic peptides and proteins and more logical searches for antivirals using amino acid sequence data and also virus specific enzymes such as the virion transcriptase as targets.

In vivo prophylactic activity of QR-435 against H3N2 influenza virus infection

BACKGROUND

Prophylaxis against influenza infection can take several forms, none of which is totally effective at preventing the spread of the disease. QR-435, an all-natural compound of green-tea extract and other agents, has been developed to protect against a range of viral infections, including the influenza subtype H3N2.

METHODS

Several different QR-435 formulations were tested against the two influenza A H3N2 viruses (A/Sydney/5/97 and A/Panama/2007/99) in the ferret model. Most experiments included negative (phosphate-buffered saline) and positive (oseltamivir 5 mg/kg, twice daily) controls. QR-435 and the control were administered 5 minutes after intranasal delivery of the virus as prophylaxis against infection resulting from exposure to infected but untreated ferrets and for prevention of transmission from infected and treated ferrets to untreated animals. Effects of QR-435 on seroconversion, virus shedding, and systemic sequelae of infection (weight loss, fever, reduced activity) were evaluated.

RESULTS

QR-435 prevented transmission and provided prophylaxis against influenza virus H3N2. Prophylaxis with QR-435 was significantly more than with oseltamivir in these experiments. Optimal in vivo efficacy of QR-435 requires a horseradish concentration of at least 50% of that in the original formulation, and the benefits of this preparation appear to be dose dependent.

CONCLUSIONS

QR-435 is effective for both prevention of H3N2 viral transmission and prophylaxis. These preclinical results warrant further evaluation of its prophylactic properties against avian influenza virus infection in humans.

Cloning, expression and characterization of ferret CXCL10

Chemokines and their receptors function in the recruitment and activation of cells of the immune system to sites of inflammation. As such, chemokines play an important role in mediating pathophysiological events during microbial infection. In particular, CXCL9, CXCL10 and CXCL11 and their cognate receptor CXCR3 have been associated with the clinical course of several infectious diseases, including severe acute respiratory syndrome (SARS) and influenza. While CXCL9, CXCL10 and CXCL11 share the same receptor and have overlapping functions, each can also have unique activity in host defense. The lack of a preferred characterized animal model for SARS has brought our attention to ferrets, which have been used for years in influenza studies. The lack of immunological reagents for ferrets prompted us to clone CXCL9, CXCL10, CXCL11 and CXCR3 and, in the case of CXCL10, to express the gene as a recombinant protein. In this study we demonstrate that endogenous ferret CXCL10 exhibits similar mRNA expression patterns in the lungs of deceased SARS patients and ferrets experimentally infected with SARS coronavirus. This study therefore represents an important step towards development of the ferret as a model for the role of CXCL9, CXCL10 and CXCL11:CXCR3 axis in severe viral infections.

Low pH gel intranasal sprays inactivate influenza viruses in vitro and protect ferrets against influenza infection

Background

Developing strategies for controlling the severity of pandemic influenza is a global public health priority. In the event of a pandemic there may be a place for inexpensive, readily available, effective adjunctive therapies to support containment strategies such as prescription antivirals, vaccines, quarantine and restrictions on travel. Inactivation of virus in the intranasal environment is one possible approach. The work described here investigated the sensitivity of influenza viruses to low pH, and the activity of low pH nasal sprays on the course of an influenza infection in the ferret model.

Methods

Inactivation of influenza A and avian reassortment influenza was determined using in vitro solutions tests. Low pH nasal sprays were tested using the ferret model with an influenza A Sydney/5/97 challenge. Clinical measures were shed virus, weight loss and body temperature.

Results

The virus inactivation studies showed that influenza viruses are rapidly inactivated by contact with acid buffered solutions at pH 3.5. The titre of influenza A Sydney/5/97 [H3N2] was reduced by at least 3 log cycles with one minute contact with buffers based on simple acid mixtures such as L-pyroglutamic acid, succinic acid, citric acid and ascorbic acid. A pH 3.5 nasal gel composition containing pyroglutamic acid, succinic acid and zinc acetate reduced titres of influenza A Hong Kong/8/68 [H3N2] by 6 log cycles, and avian reassortment influenza A/Washington/897/80 X A Mallard/New York/6750/78 [H3N2] by 5 log cycles, with 1 min contact.

Two ferret challenge studies, with influenza A Sydney/5/97, demonstrated a reduction in the severity of the disease with early application of low pH nasal sprays versus a saline control. In the first study there was decreased weight loss in the treatment groups. In the second study there were reductions in virus shedding and weight loss, most notably when a gelling agent was added to the low pH formulation.

Conclusion

These findings indicate the potential of a low pH nasal spray as an adjunct to current influenza therapies, and warrant further investigation in humans.

Vaccination with formalin-inactivated influenza vaccine protects mice against lethal influenza Streptococcus pyogenes superinfection

Intranasal infection with non-lethal influenza A virus (IAV) followed by infection with group A streptococci (GAS) induces invasive, lethal GAS infections, including necrotizing fasciitis, in mice. We demonstrate that subcutaneous immunization of formalin-inactivated IAV vaccine or intranasal immunization of IAV vaccine and cholera toxin protected more than 75% of mice from death by lethal IAV-GAS superinfection. The increased survival rate correlates with increase in IAV neutralizing activity and the levels of serum anti-IAV IgG. Moreover, elimination of IAV from the lungs of vaccinated mice led to depletion of GAS associated with alveolar epithelial cells. These findings suggest that formalin-inactivated IAV vaccine may be useful for prevention of secondary bacterial infections following prior IAV exposure.

The role of M cells of human nasopharyngeal lymphoid tissue in influenza virus sampling

Little is known about the role of the M cells of human nasopharyngeal lymphoid tissue in the sampling of viruses that cause respiratory infections. To clarify whether M cells could function as a gateway for influenza virus into human nasopharyngeal lymphoid tissue, excised adenoid tissue was incubated in media containing influenza A virus for 30, 60, and 90 min, respectively. Transmission electron microscopic observation revealed that many influenza viruses adhered to M cell surfaces and were taken up into the cytoplasmic vesicles of M cells after 30 min incubation; the viruses had been transported into enfolded lymphoid cells after 60 min incubation. By staining M cells with Sambucus nigra lectin, which specifically recognizes the NeuAcalpha2,6 Gal linkage of sialoprotein, it was also found that abundant receptors for the human influenza virus are present on the M cell surface. Our findings indicated that M cells of human nasopharyngeal tonsils function as a major port for influenza A virus entry and that the virus could be efficiently transferred to enfolded macrophages and lymphoid cells by M cells. The transport of influenza viruses to lymphoid cells by M cells may promote antigen delivery to the immune system, and these findings may be important for systemic delivery of those influenza viruses that have the capacity to productively infect cells outside of the respiratory tract.

Changes in calcium currents and GABAergic spontaneous activity in cultured rat hippocampal neurons after a neurotropic influenza A virus infection

In order to study mechanisms by which a neurotropic strain of influenza A virus (A/WSN/33) may affect neuronal function or cause nerve cell death, hippocampal cultures from embryonic rats were infected with this virus. Approximately 70% of the neurons in the infected cultures became immunopositive for viral antigens and showed reduced voltage-dependent Ca(2+) currents in whole-cell patch clamp recordings, but no changes in other membrane properties or in cytosolic Ca(2+) concentration were seen. These immunopositive neurons underwent apoptosis 3-4 days after infection. Ca(2+) channel inhibitors had no significant effect on neuronal survival. The immunonegative population of neurons survived, but displayed increased frequency of miniature inhibitory postsynaptic currents of gamma-amino-butyric acid origin compared with controls. The frequency of alpha-amino-hydroxy-5-methylisoxazole-4-propionic acid hydrobromide (AMPA) receptor-mediated miniature excitatory postsynaptic currents was not altered. Viral nucleoproteins, overexpressed using the Semliki Forest virus system, were localized to the dendritic spines as shown by double immunolabeling with actinin, but did not by themselves cause neuronal death or changes in synaptic transmission as measured by AMPA-mediated excitatory postsynaptic currents. Our results show that an influenza A virus infection can cause selective neurophysiological changes in hippocampal neurons and that these can persist even after the viral antigens have been cleared.

Efficacy of zanamivir against avian influenza A viruses that possess genes encoding H5N1 internal proteins and are pathogenic in mammals

In 1997, an avian H5N1 influenza virus, A/Hong Kong/156/97 (A/HK/156/97), caused six deaths in Hong Kong, and in 1999, an avian H9N2 influenza virus infected two children in Hong Kong. These viruses and a third avian virus [A/Teal/HK/W312/97 (H6N1)] have six highly related genes encoding internal proteins. Additionally, A/Chicken/HK/G9/97 (H9N2) virus has PB1 and PB2 genes that are highly related to those of A/HK/156/97 (H5N1), A/Teal/HK/W312/97 (H6N1), and A/Quail/HK/G1/97 (H9N2) viruses. Because of their similarities with the H5N1 virus, these H6N1 and H9N2 viruses may have the potential for interspecies transmission. We demonstrate that these H6N1 and H9N2 viruses are pathogenic in mice but that their pathogenicities are less than that of A/HK/156/97 (H5N1). Unadapted virus replicated in lungs, but only A/HK/156/97 (H5N1) was found in the brain. After three passages (P3) in mouse lungs, the pathogenicity of the viruses increased, with both A/Teal/HK/W312/97 (H6N1) (P3) and A/Quail/HK/G1/97 (H9N2) (P3) viruses being found in the brain. The neuraminidase inhibitor zanamivir inhibited viral replication in Madin-Darby canine kidney cells in virus yield assays (50% effective concentration, 8.5 to 14.0 microM) and inhibited viral neuraminidase activity (50% inhibitory concentration, 5 to 10 nM). Twice daily intranasal administration of zanamivir (50 and 100 mg/kg of body weight) completely protected infected mice from death. At a dose of 10 mg/kg, zanamivir completely protected mice from infection with H9N2 viruses and increased the mean survival day and the number of survivors infected with H6N1 and H5N1 viruses. Zanamivir, at all doses tested, significantly reduced the virus titers in the lungs and completely blocked the spread of virus to the brain. Thus, zanamivir is efficacious in treating avian influenza viruses that can be transmitted to mammals.

Genomic analysis of matrix gene and antigenic studies of its gene product (M1) of a swine influenza virus (H1N1) causing chronic respiratory disease in pigs

The nucleotide sequence of gene coding for the matrix protein (M1 and M2) of swine influenza (H1N1) virus, A/Sw/Quebec/5393/91 (SwQc91), associated with chronic respiratory disease in pigs, was determined. The deduced amino acid (aa) sequence was compared with the other North American swine strains including the A/Sw/Quebec/192/81 (SwQc81) strain associated with the chronic and acute respiratory disease in pigs. Separate analysis of the M1 and M2 gene products showed different evolutions. M1 had 2 aas changes among 252 aas and these were at positions 4 and 205. The mutation rate was 0.08%, aa changes per residue per year, and its homology with other strains was 99.2%. The M2 protein (97 aas) was relatively more variable than M1 with 5 substitutions. Differences observed were at positions 4, 16, 21, 54 and 95. The mutation rate was 0.51% and its homology with other strains was 94.8%. The M1 gene was cloned in the procaryotic plasmid pET21a and the recombinant plasmid was expressed in Escherichia coli under pre-determined optimal conditions. The recombinant M1 protein (RM1P) (approximately 28 kDa) comigrated as a single band on SDS-PAGE. RM1P was antigenic and reacted with polyclonal sera and 5 monoclonal antibodies (MAbs) spanning 4 epitopes including the membrane binding site and the transcription inhibition activity site. RM1P was immunogenic. The mouse anti-RM1P ELISA antibodies reacted with the purified viral M1 protein and the whole virus.

The role of alpha/beta and gamma interferons in development of immunity to influenza A virus in mice

During influenza virus infection innate and adaptive immune defenses are activated to eliminate the virus and thereby bring about recovery from illness. Both arms of the adaptive immune system, antibody neutralization of free virus and termination of intracellular virus replication by antiviral cytotoxic T cells (CTLs), play pivotal roles in virus elimination and protection from disease. Innate cytokine responses, such as alpha/beta interferon (IFN-alpha/beta) or IFN-gamma, can have roles in determining the rate of virus replication in the initial stages of infection and in shaping the initial inflammatory and downstream adaptive immune responses. The effect of these cytokines on the replication of pneumotropic influenza A virus in the respiratory tract and in the regulation of adaptive antiviral immunity was examined after intranasal infection of mice with null mutations in receptors for IFN-alpha/beta, IFN-gamma, and both IFNs. Virus titers in the lungs of mice unable to respond to IFNs were not significantly different from congenic controls for both primary and secondary infection. Likewise the mice were comparably susceptible to X31 (H3N2) influenza virus infection. No significant disruption to the development of normal antiviral CTL or antibody responses was observed. In contrast, mice bearing the disrupted IFN-alpha/beta receptor exhibited accelerated kinetics and significantly higher levels of neutralizing antibody activity during primary or secondary heterosubtypic influenza virus infection. Thus, these observations reveal no significant contribution for IFN-controlled pathways in shaping acute or memory T-cell responses to pneumotropic influenza virus infection but do indicate some role for IFN-alpha/beta in the regulation of antibody responses. Recognizing the pivotal role of CTLs and antibody in virus clearance, it is reasonable to assume a redundancy in IFN-mediated antiviral effects in pulmonary influenza. However, IFN-alpha/beta seems to be a valid factor in determining tissue tropism and replicative rates of highly virulent influenza virus strains as reported previously by others, and this aspect is discussed here.

Therapeutic effect of anti-macrophage inflammatory protein 2 antibody on influenza virus-induced pneumonia in mice

We investigated the effect of anti-macrophage inflammatory protein 2 immunoglobulin G (aMIP-2 IgG) on the progression of influenza virus-induced pneumonia in mice. When mice were infected with a mouse lung-adapted strain of influenza A/PR/8/34 virus by intranasal inoculation, neutrophil counts in the bronchoalveolar lavage fluid (BALF) increased in parallel with the kinetics of MIP-2 production, which peaked 2 days after infection. After intracutaneous injection of a dose of 10 or 100 microg of aMIP-2 IgG once a day on days 0 and 1, neutrophil counts in BALF on day 2 were reduced to 49 or 37%, respectively, of the value in the control infected mice administered anti-protein A IgG. The antibody administration also improved lung pathology without affecting virus replication. Furthermore, by prolonged administration with a higher or lower dose for up to 5 days, body weight loss became slower and finally 40% of mice in both treatment groups survived potentially lethal pneumonia. These findings suggest that MIP-2-mediated neutrophil infiltration during the early phase of infection might play an important role in lung pathology. Thus, MIP-2 was considered to be a novel target for intervention therapy in potentially lethal influenza virus pneumonia in mice.

Role of hemagglutinin cleavage for the pathogenicity of influenza virus

Although human epidemics of influenza occur on nearly an annual basis and result in a significant number of "excess deaths," the viruses responsible are not generally considered highly pathogenic. On occasion, however, an outbreak occurs that demonstrates the potential lethality of influenza viruses. The human pandemic of 1918 spread worldwide and killed millions, and the limited human outbreak of highly pathogenic avian viruses in Hong Kong at the end of 1997 is a warning that this could happen again. In avian species such as chickens and turkeys, several outbreaks of highly pathogenic influenza viruses have been documented. Although the reason for the lethality of the human 1918 viruses remains unclear, the pathogenicity of the avian viruses, including those that caused the human 1997 outbreak, relates primarily to properties of the hemagglutinin glycoprotein (HA). Cleavage of the HA precursor molecule HA0 is required to activate virus infectivity, and the distribution of activating proteases in the host is one of the determinants of tropism and, as such, pathogenicity. The HAs of mammalian and nonpathogenic avian viruses are cleaved extracellularly, which limits their spread in hosts to tissues where the appropriate proteases are encountered. On the other hand, the HAs of pathogenic viruses are cleaved intracellularly by ubiquitously occurring proteases and therefore have the capacity to infect various cell types and cause systemic infections. The x-ray crystal structure of HA0 has been solved recently and shows that the cleavage site forms a loop that extends from the surface of the molecule, and it is the composition and structure of the cleavage loop region that dictate the range of proteases that can potentially activate infectivity. Here influenza virus pathogenicity is discussed, with an emphasis on the role of HA0 cleavage as a determining factor.

Influenza A Virus Accelerates Neutrophil Apoptosis and Markedly Potentiates Apoptotic Effects of Bacteria

Neutrophils are recruited into the airway in the early phase of uncomplicated influenza A virus (IAV) infection and during the bacterial superinfections that are a significant cause of morbidity and mortality in IAV-infected subjects. In this report, we show that IAV accelerates neutrophil apoptosis. Unopsonized Escherichia colihad similar effects, although apoptotic effects of opsonized E coli were greater. When neutrophils were treated with both IAV and unopsonized E coli, a marked enhancement of the rate and extent of neutrophil apoptosis occured as compared with that caused by either pathogen alone. Treatment of neutrophils with IAV markedly increased phagocytosis of E coli. Simultaneous treatment of neutrophils with IAV and E coli also elicited greater hydrogen peroxide production than did either pathogen alone. IAV increased neutrophil expression of Fas antigen and Fas ligand, and it also increased release of Fas ligand into the cell supernatant. These findings may have relevance to the understanding of inflammatory responses to IAV in vivo and of bacterial superinfection of IAV-infected subjects.