Research on influenza virus in LM-S laboratory is partially funded by The New York Influenza Center of Excellence (NYICE), a member of the NIAID Centers of Excellence for Influenza Research and Surveillance (CEIRS). We thank Wendy Bates for her support in the corrections of the manuscript.

<ol>
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The authors have nothing to disclose.

The mouse model of IAV is widely used for in vivo studies of IAV pathogenesis, immunogenicity and protection efficacy. The small size of mice makes them easy to manipulate and store as compared to other animal models such as ferrets or guinea pigs. Moreover, the ease in terms of animal cost, housing and reproduction allow their use in pre-clinical vaccination tests in which large numbers of animals are needed. Notably, since mice have been used in multiple research disciplines, several molecular and immunology m...

IAVs are enveloped viruses classified in the Orthomyxoviridae family3. They contain eight single-stranded RNA molecules with negative polarity3. In humans, IAVs cause seasonal epidemics and occasional pandemics of important consequence when novel viruses are introduced in the human population4. Moreover, seasonal IAVs are highly and rapidly transmitted between humans producing an elevated economic loss worldwide every year2,5. IAV symptoms include cough, nasal congestion, fever, malaise, headache, anorexia and myalgia, but the virus can also produce a more severe disease in immunocompromised patients6. In fact, the World Health Organization (WHO) calculates that seasonal influenza viruses cause 300,000 - 500,000 deaths worldwide every year1. There are only two classes of drugs currently approved by the Food and Drug Administration (FDA) for influenza prophylaxis and treatment in humans: neuraminidase (NA) inhibitors (e.g., oseltamivir) and blockers of the M2 ion channel (e.g., amantadine); however, the emergence of drug-resistant virus variants is an increasing concern. Vaccination, therefore, remains the best medical option to protect humans against IAVs infections. To date, three types of influenza vaccines licensed by the FDA for human use are available: recombinant viral hemagglutinin (HA) protein vaccines, inactivated influenza vaccines (IIV), and live-attenuated influenza vaccines (LAIV)5,7. The three vaccines are designed to induce adaptive immune response against the viral HA protein, the major target of neutralizing antibodies against IAVs.
A validated mouse model to study IAV infection in vivo
Animal models have been used to study, among others, IAV pathogenesis8,9,10,11, viral factors that contribute to disease12 and/or viral transmission13,14, and to test the efficacy of new vaccines or antiviral drugs9,10,15. Mice (Mus musculus) are the most extensively used animal model for IAV research for several reasons: 1) the immune system is evolutionarily similar to that present in humans; 2) low cost, including animal purchase, housing and reproduction; 3) small size to easily manipulate and store; 4) minimal host variability to obtain homogeneous responses and results; 5) a large knowledge of mice biology, including genome sequence; 6) many available molecular biology and/or immunology reagents; 7) available knock out (KO) mice to study the contribution of a given host protein on viral infection; and, 8) multiple mouse strains that can be exploited to evaluate the genetic basis of infections.
There are several mouse strains currently available to study IAV in vivo. Age, immune status, sex, genetic background and mouse strain as well as routes of infection, dose and viral strains all influence the outcome of IAV infection in mice. The most common mouse strains used in IAV research are C57BL/6, BALB/C and, more recently, DBA.2 mice since they are more susceptible to IAV disease than the two former strains16,17,18,19,20. Importantly, the immune response also can be different depending on the mouse strain18,19,20. Thus, it is very important to recover all the available information about the mouse and IAV strain to choose the best option for the experiment to be conducted.
Although mouse is a good animal model of infection for in vivo studies with IAV, they have several limitations, which need to be considered in the experimental design. For instance, a major limitation of using mice for in vivo studies is that IAVs do not transmit among mice. Thus, for transmission studies, more accepted animal models (e.g., ferrets or guinea pigs) are used16,17,21. In addition, there are several differences between the manifestations of IAV in mice and humans. Unlike humans, mice do not develop fever upon IAV infection; conversely they present with hypothermia16,17. In mice, IAV replication is concentrated in the lower respiratory tract (lungs) rather than the upper airways. Thus, virulence of IAV in mice is not always correlated to that seen in humans. Altogether, because the advantages outweigh the limited disadvantages, mouse represents the first animal model used to evaluate influenza viral pathogenesis, immunogenicity and protective efficacy in vaccine and antiviral studies. Moreover, it would not be ethically acceptable to conduct studies with IAV using large animal models without previous evidence in a small animal model of IAV infection. In this manuscript, we describe how to infect mice intranasally (i.n.) with IAV, how to monitor the severity and progress of viral infection and how to carry out the experiments required to evaluate humoral immune responses and protection efficacy.

<table border="0" cellpadding="0" cellspacing="0" width="656">
	<tbody>
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			<td height="40" style="height:40px;width:295px;">Madin-Darby Canine Kidney (MDCK) epithelial cells</td>
			<td style="width:119px;">ATCC</td>
			<td style="width:123px;">CCL-34</td>
			<td style="width:121px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:295px;">Six- to eight-week-old female C57BL/6 mice</td>
			<td style="width:119px;">National Cancer Institute (NCI)</td>
			<td>01XBE</td>
			<td style="width:121px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Turckey red blod cells</td>
			<td style="width:119px;">Biolink Inc</td>
			<td style="width:123px;"></td>
			<td style="width:121px;">Store at 4&#176;C</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Dulbecco&#8217;s modified Eagle&#8217;s medium (DMEM)</td>
			<td style="width:119px;">Corning Cellgro</td>
			<td style="width:123px;">15-013-CV</td>
			<td style="width:121px;">Store at 4&#176;C</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Fetal Bovine Serum (FBS)</td>
			<td style="width:119px;">Seradigm</td>
			<td style="width:123px;">1500-050</td>
			<td style="width:121px;">Store at -20&#176;C</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:295px;">Penicillin/Streptomycin/L-Glutamine (PSG) 100X</td>
			<td style="width:119px;">Corning</td>
			<td style="width:123px;">30-009-CI</td>
			<td style="width:121px;">Store at -20&#176;C</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Penicillin/Streptomycin (PS) 100X</td>
			<td style="width:119px;">Corning</td>
			<td style="width:123px;">30-00-CI</td>
			<td style="width:121px;">Store at -20&#176;C</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Bovin Albumin solution (BA)</td>
			<td style="width:119px;">Sigma-Aldrich</td>
			<td style="width:123px;">A7409</td>
			<td style="width:121px;">Store at 4&#176;C</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Bovin Serum Albumin (BSA)</td>
			<td style="width:119px;">Sigma-Aldrich</td>
			<td style="width:123px;">A9647</td>
			<td style="width:121px;">Store at 4&#176;C</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:295px;">Tosylsulfonyl phenylalanyl chloromethyl ketone (TPCK)-treated trypsin</td>
			<td style="width:119px;">Sigma-Aldrich</td>
			<td style="width:123px;">T8802</td>
			<td style="width:121px;">Store at -20&#176;C</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Neutral Buffered Formalin 10%</td>
			<td style="width:119px;">EMD</td>
			<td style="width:123px;">65346-85</td>
			<td style="width:121px;">Store at RT</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Triton X-100</td>
			<td style="width:119px;">J.T.Baker</td>
			<td style="width:123px;">X198-07</td>
			<td style="width:121px;">Store at RT</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:295px;">Monoclonal Antibody anti-NP Influenza A Virus HB-65</td>
			<td style="width:119px;">ATTC</td>
			<td style="width:123px;">H16-L10-4R5</td>
			<td style="width:121px;">Store at -20&#176;C</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:295px;">Polyclonal rabbit anti-mouse immunoglobulins/FITC</td>
			<td style="width:119px;">Dako</td>
			<td style="width:123px;">F0261</td>
			<td style="width:121px;">Store at 4&#176;C</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:295px;">ECL Anti-mouse IgG, Horseradish Peroxidase linked whole antibody</td>
			<td style="width:119px;">GE Healthcare</td>
			<td style="width:123px;">LNA931V/AG</td>
			<td style="width:121px;">Store at 4&#176;C</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">TMB substrate set</td>
			<td style="width:119px;">BioLegend</td>
			<td style="width:123px;">421101</td>
			<td style="width:121px;">Store at 4&#176;C</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:295px;">Vmax Kinetic plate reader</td>
			<td style="width:119px;">Molecular Devices</td>
			<td style="width:123px;"></td>
			<td style="width:121px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Dounce Tissue Grinders</td>
			<td style="width:119px;">Thomas Scientific</td>
			<td style="width:123px;">7722-7</td>
			<td style="width:121px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Receptor destroying enzyme, RDE (II)</td>
			<td style="width:119px;">Denka Seiken Co.</td>
			<td style="width:123px;">370013</td>
			<td style="width:121px;">Store at -20&#176;C</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Crystal Violet</td>
			<td style="width:119px;">Fisher Scienctific</td>
			<td style="width:123px;">C581-100</td>
			<td style="width:121px;">Store at RT</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">96-well Cell Culture Plate</td>
			<td style="width:119px;">Greiner Bio-one</td>
			<td style="width:123px;">655-180</td>
			<td style="width:121px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Cell Culture dishes 100mm</td>
			<td style="width:119px;">Greiner Bio-one</td>
			<td style="width:123px;">664-160</td>
			<td style="width:121px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:295px;">Nunc MicroWell 96-Well Microplates</td>
			<td style="width:119px;">Thermo Fisher Scienctific</td>
			<td style="width:123px;">269620</td>
			<td style="width:121px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:295px;">Nunc 96-Well Polystyrene Conical Bottom MicroWell Plates</td>
			<td style="width:119px;">Thermo Fisher Scienctific</td>
			<td style="width:123px;">249570</td>
			<td style="width:121px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Puralub Vet Ointment</td>
			<td style="width:119px;">Dechra</td>
			<td style="width:123px;">9N-76855</td>
			<td style="width:121px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:295px;">Fluorescent microscope</td>
			<td style="width:119px;">Olympus</td>
			<td>Olympus IX81</td>
			<td style="width:121px;"></td>
		</tr>
	</tbody>
</table>

influenza a virus studies in a mouse model of infection

Influenza viruses cause over 500,000 deaths worldwide1 and are associated with an annual cost of 12 - 14 billion USD in the United States alone considering direct medical and hospitalization expenses and work absenteeism2. Animal models are crucial in Influenza A virus (IAV) studies to evaluate viral pathogenesis, host-pathogen interactions, immune responses, and the efficacy of current and/or novel vaccine approaches as well as antivirals. Mice are an advantageous small animal model because their immune system is evolutionarily similar to that found in humans, they are available from commercial vendors as genetically identical subjects, there are multiple strains that can be exploited to evaluate the genetic basis of infections, and they are relatively inexpensive and easy to manipulate. To recapitulate IAV infection in humans via the airways, mice are first anesthetized prior to intranasal inoculation with infectious IAVs under proper biosafety containment. After infection, the pathogenesis of IAVs is determined by monitoring daily the morbidity (body weight loss) and mortality (survival) rate. In addition, viral pathogenesis can also be evaluated by assessing virus replication in the upper (nasal mucosa) or lower (lungs) respiratory tract of infected mice. Humoral responses upon IAV infection can be rapidly evaluated by non-invasive bleeding and secondary antibody detection assays aimed at detecting the presence of total or neutralizing antibodies. Here, we describe the common methods used to infect mice intranasally (i.n) with IAV and evaluate pathogenesis, humoral immune responses and protection efficacy.

Characterization of viral pathogenesis in mice
The pathogenesis of IAV is related to the morbidity and mortality caused by its infection. These two parameters can be evaluated in mice easily: IAV morbidity is associated with body weight loss in infected mice and the percentage of survival will indicate the mortality rate (Figure 1). The body weight and survival in IAV-infected mice are usually monitore...

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Influenza A Virus Studies in a Mouse Model of Infection

Influenza A viruses (IAVs) are important human respiratory pathogens. To understand the pathogenicity of IAVs and to perform preclinical testing of novel vaccine approaches, animal models mimicking human physiology are required. Here, we describe techniques to evaluate IAV pathogenesis, humoral responses and vaccine efficacy using a mouse model of infection.

Influenza viruses cause over 500,000 deaths worldwide1 and are associated with an annual cost of 12 - 14 billion USD in the United States alone ...

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28.1K Views.  University of Rochester School of Medicine and Dentistry. Influenza A viruses (IAVs) are important human respiratory pathogens. To understand the pathogenicity of IAVs and to perform preclinical testing of novel vaccine approaches, animal models mimicking human physiology are required. Here, we describe techniques to evaluate IAV pathogenesis, humoral responses and vaccine efficacy using a mouse model of infection.

Video: Influenza A Virus Studies in a Mouse Model of Infection

Using Bioluminescent Imaging to Investigate Synergism Between Streptococcus pneumoniae and Influenza A Virus in Infant Mice

During the 1918 influenza virus pandemic, which killed approximately 50 million people worldwide, the majority of fatalities were not the result of infection with influenza virus alone. Instead, most individuals are thought to have succumbed to a secondary bacterial infection, predominately caused by the bacterium Streptococcus pneumoniae (the pneumococcus). The synergistic relationship between infections caused by influenza virus and the pneumococcus has subsequently been observed during the 1957 Asian influenza virus pandemic, as well as during seasonal outbreaks of the virus (reviewed in 1, 2). Here, we describe a protocol used to investigate the mechanism(s) that may be involved in increased morbidity as a result of concurrent influenza A virus and S. pneumoniae infection. We have developed an infant murine model to reliably and reproducibly demonstrate the effects of influenza virus infection of mice colonised with S. pneumoniae. Using this protocol, we have provided the first insight into the kinetics of pneumococcal transmission between co-housed, neonatal mice using in vivo imaging 3.

Using Bioluminescent Imaging to Investigate Synergism Between Streptococcus pneumoniae and Influenza A Virus in Infant Mice

A concurrent infection with influenza A virus is one of the factors implicated in the induction of invasive pneumococcal disease during asymptomatic Streptococcus pneumoniae carriage. Here we describe a mixed infection method using infant mice to investigate the synergism between these two respiratory pathogens.

During the 1918 influenza virus pandemic, which killed approximately 50 million people worldwide, the majority of fatalities were not the result of ...

Influenza Virus Propagation in Embryonated Chicken Eggs

Influenza infection is associated with about 36,000 deaths and more than 200,000 hospitalizations every year in the United States. The continuous emergence of new influenza virus strains due to mutation and re-assortment complicates the control of the virus and necessitates the permanent development of novel drugs and vaccines. The laboratory-based study of influenza requires a reliable and cost-effective method for the propagation of the virus. Here, a comprehensive protocol is provided for influenza A virus propagation in fertile chicken eggs, which consistently yields high titer viral stocks. In brief, serum pathogen-free (SPF) fertilized chicken eggs are incubated at 37 &#176;C and 55-60% humidity for 10 &#8211; 11 days. Over this period, embryo development can be easily monitored using an egg candler. Virus inoculation is carried out by injection of virus stock into the allantoic cavity using a needle. After 2 days of incubation at 37 &#176;C, the eggs are chilled for at least 4 hr at 4 &#176;C. The eggshell above the air sac and the chorioallantoic membrane are then carefully opened, and the allantoic fluid containing the virus is harvested. The fluid is cleared from debris by centrifugation, aliquoted and transferred to -80 &#176;C for long-term storage. The large amount (5-10 ml of virus-containing fluid per egg) and high virus titer which is usually achieved with this protocol has made the usage of eggs for virus preparation our favorable method, in particular for in vitro studies which require large quantities of virus in which high dosages of the same virus stock are needed.

Fertile chicken eggs are widely used to produce large amounts of human influenza A virus as they provide a convenient and cost-effective system to prove high yields of virus.

Influenza infection is associated with about 36,000 deaths and more than 200,000 hospitalizations every year in the United States. The continuous ...

Co-immunoprecipitation of the Mouse Mx1 Protein with the Influenza A Virus Nucleoprotein

Studying the interaction between proteins is key in understanding their function(s). A very powerful method that is frequently used to study interactions of proteins with other macromolecules in a complex sample is called co-immunoprecipitation. The described co-immunoprecipitation protocol allows to demonstrate and further investigate the interaction between the antiviral myxovirus resistance protein 1 (Mx1) and one of its viral targets, the influenza A virus nucleoprotein (NP). The protocol starts with transfected mammalian cells, but it is also possible to use influenza A virus infected cells as starting material. After cell lysis, the viral NP protein is pulled-down with a specific antibody and the resulting immune-complexes are precipitated with protein G beads. The successful pull-down of NP and the co-immunoprecipitation of the antiviral Mx1 protein are subsequently revealed by western blotting. A prerequisite for successful co-immunoprecipitation of Mx1 with NP is the presence of N-ethylmaleimide (NEM) in the cell lysis buffer. NEM alkylates free thiol groups. Presumably this reaction stabilizes the weak and/or transient NP&#8211;Mx1 interaction by preserving a specific conformation of Mx1, its viral target or an unknown third component. An important limitation of co-immunoprecipitation experiments is the inadvertent pull-down of contaminating proteins, caused by nonspecific binding of proteins to the protein G beads or antibodies. Therefore, it is very important to include control settings to exclude false positive results. The described co-immunoprecipitation protocol can be used to study the interaction of Mx proteins from different vertebrate species with viral proteins, any pair of proteins, or of a protein with other macromolecules. The beneficial role of NEM to stabilize weak and/or transient interactions needs to be tested for each interaction pair individually.

This co-immunoprecipitation protocol allows to study the interaction between the influenza A virus nucleoprotein and the antiviral Mx1 protein in human cells. The protocol emphasizes the importance of N-ethylmaleimide for successful co-immunoprecipitation of Mx1 and influenza A virus nucleoprotein.

Studying the interaction between proteins is key in understanding their function(s). A very powerful method that is frequently used to study interactions ...

Nasal Wipes for Influenza A Virus Detection and Isolation from Swine

Surveillance for influenza A viruses in swine is critical to human and animal health because influenza A virus rapidly evolves in swine populations and new strains are continually emerging. Swine are able to be infected by diverse lineages of influenza A virus making them important hosts for the emergence and maintenance of novel influenza A virus strains. Sampling pigs in diverse settings such as commercial swine farms, agricultural fairs, and live animal markets is important to provide a comprehensive view of currently circulating IAV strains. The current gold-standard ante-mortem sampling technique (i.e. collection of nasal swabs) is labor intensive because it requires physical restraint of the pigs. Nasal wipes involve rubbing a piece of fabric across the snout of the pig with minimal to no restraint of the animal. The nasal wipe procedure is simple to perform and does not require personnel with professional veterinary or animal handling training. While slightly less sensitive than nasal swabs, virus detection and isolation rates are adequate to make nasal wipes a viable alternative for sampling individual pigs when low stress sampling methods are required. The proceeding protocol outlines the steps needed to collect a viable nasal wipe from an individual pig.

The authors present a protocol to collect swine nasal wipes to detect and isolate influenza A viruses.

Surveillance for influenza A viruses in swine is critical to human and animal health because influenza A virus rapidly evolves in swine populations and ...

Measuring Attachment and Internalization of Influenza A Virus in A549 Cells by Flow Cytometry

Attachment to target cells followed by internalization are the very first steps of the life cycle of influenza A virus (IAV). We provide here a detailed protocol for measuring relative changes in the amount of viral particles that attach to A549 cells, a human lung epithelial cell line, as well as in the amount of particles that are internalized into the cell. We use biotinylated virus which can be easily detected following staining with Cy3-labeled streptavidin (STV-Cy3). We describe the growth, purification and biotinylation of A/WSN/33, a widely used IAV laboratory strain. Cold-bound biotinylated IAV particles on A549 cells are stained with STV-Cy3 and measured using flow cytometry. To investigate uptake of viral particles, cold-bound virus is allowed to internalize at 37 &#176;C. In order to differentiate between external and internalized viral particles, a blocking step is applied: Free binding spots on the biotin of attached virus on the cell surface are bound by unlabeled streptavidin (STV). Subsequent cell permeabilization and staining with STV-Cy3 then enables detection of internalized viral particles. We present a calculation to determine the relative amount of internalized virus. This assay is suitable to measure effects of drug-treatments or other manipulations on attachment or internalization of IAV.

We present a protocol describing a semi-quantitative method for measuring both, the attachment of influenza A virus to A549 cells, as well as the internalization of virus particles into the target cells by flow cytometry.

Attachment to target cells followed by internalization are the very first steps of the life cycle of influenza A virus (IAV). We provide here a detailed ...

Neutrophil Isolation and Analysis to Determine their Role in Lymphoma Cell Sensitivity to Therapeutic Agents

Neutrophils are the most abundant (40% to 75%) type of white blood cells and among the first inflammatory cells to migrate towards the site of inflammation. They are key players in the innate immune system and play major roles in cancer biology. Neutrophils have been proposed as key mediators of malignant transformation, tumor progression, angiogenesis and in the modulation of the antitumor immunity; through their release of soluble factors or their interaction with tumor cells. To characterize the specific functions of neutrophils, a fast and reliable method is coveted for in vitro isolation of neutrophils from human blood. Here, a density gradient separation method is demonstrated to isolate neutrophils as well as mononuclear cells from the blood. The procedure consists of layering the density gradient solution such as Ficoll carefully above the diluted blood obtained from patients diagnosed with chronic lymphocytic leukemia (CLL), followed by centrifugation, isolation of mononuclear layer, separation of neutrophils from RBCsby dextran then lysis of residual erythrocytes. This method has been shown to isolate neutrophils &#8805; 90 % pure. To mimic the tumor microenvironment, 3-dimensional (3D) experiments were performed using basement membrane matrix such as Matrigel. Given the short half-life of neutrophils in vitro, 3D experiments with fresh human neutrophils cannot be performed. For this reason promyelocytic HL60 cells are differentiated along the granulocytic pathway using the differentiation inducers dimethyl sulfoxide (DMSO) and retinoic acid (RA). The aim of our experiments is to study the role of neutrophils on the sensitivity of lymphoma cells to anti-lymphoma agents. However these methods can be generalized to study the interactions of neutrophils or neutrophil-like cells with a large range of cell types in different situations.

Neutrophils are the most abundant type of white blood cells. The isolation of neutrophils from human blood by density gradient separation method and the differentiation of human promyelocytic (HL60) cells along the granulocytic pathway are described here; to test their role on sensitivity of lymphoma cells to anti-lymphoma agents.

Neutrophils are the most abundant (40% to 75%) type of white blood cells and among the first inflammatory cells to migrate towards the site of ...

A Miniaturized Glycan Microarray Assay for Assessing Avidity and Specificity of Influenza A Virus Hemagglutinins

Influenza A virus (IAV) hemagglutinins recognize sialic acids on the cell surface as functional receptors to gain entry into cells. Wild waterfowl are the natural reservoir for IAV, but IAV can cross the species barrier to poultry, swine, horses and humans. Avian viruses recognize sialic acid attached to a penultimate galactose by a &#945;2-3 linkage (avian-type receptors) whereas human viruses preferentially recognize sialic acid with a &#945;2-6 linkage (human-type receptors). To monitor if avian viruses are adapting to human type receptors, several methods can be used. Glycan microarrays with diverse libraries of synthetic sialosides are increasingly used to evaluate receptor specificity. However, this technique is not used for measuring avidities. Measurement of avidity is typically achieved by evaluating the binding of serially diluted hemagglutinin or virus to glycans adsorbed to conventional polypropylene 96-well plates. In this assay, glycans with &#945;2-3 or &#945;2-6 sialic acids are coupled to biotin and adsorbed to streptavidin plates, or are coupled to polyacrylamide (PAA) which directly adsorb to the plastic. We have significantly miniaturized this assay by directly printing PAA-linked sialosides and their non PAA-linked counterparts on micro-well glass slides. This set-up, with 48 arrays on a single slide, enables simultaneous assays of 6 glycan binding proteins at 8 dilutions, interrogating 6 different glycans, including two non-sialylated controls. This is equivalent to 18x 96-well plates in the traditional plate assay. The glycan array format decreases consumption of compounds and biologicals and thus greatly enhances efficiency.

Using a printed glycan microarray strategy, a conventional 96-well plate assay was miniaturized for analysis of influenza A virus hemagglutinin avidity and specificity for sialic acid containing receptors.

Influenza A virus (IAV) hemagglutinins recognize sialic acids on the cell surface as functional receptors to gain entry into cells. Wild waterfowl are the ...

In Vitro Disassembly of Influenza A Virus Capsids by Gradient Centrifugation

Acid-triggered molecular processes closely control cell entry of many viruses that enter through the endocytic system. In the case of influenza A virus (IAV), virus fusion with the endosomal membrane as well as the subsequent disassembly of the viral capsid, called uncoating, is governed by the ionic conditions inside endocytic vesicles. The early steps in the virus life cycle are hard to study because endosomes cannot be directly accessed experimentally, creating the need for an in vitro approach. Here, we describe a method based on velocity gradient centrifugation of purified virions through a two-layer glycerol gradient, which enables analysis of the IAV core and its stability. The gradient contains a non-ionic detergent (NP-40) in its lower layer to remove the viral membrane by solubilization as the virus sediments toward the bottom. At neutral pH, viral cores are pelleted as stable structures. The major core components, matrix protein (M1) and the viral ribonucleoproteins (vRNPs), can be clearly identified in the pellet fraction by SDS-PAGE. Decreasing the pH to 6.0 or lower in the bottom layer selectively removes M1 from the pellet followed by release of vRNPs at more acidic conditions. Viral protein bands on Coomassie-stained gels can be subjected to densitometric quantification to monitor intermediate states of IAV disassembly. Besides pH, other factors that influence viral core stability can be assessed, such as salt concentration and putative viral uncoating factors, simply by modifying the detergent-containing glycerol layer accordingly. Taken together, the presented technique allows highly reproducible and quantitative analysis of viral uncoating in vitro. It can be applied to other enveloped viruses that undergo complex uncoating processes.

In Vitro Disassembly of Influenza A Virus Capsids by Gradient Centrifugation

Disassembly of influenza A virus cores during virus entry into host cells is a multistep process. We describe an in vitro method to analyze the early stages of viral uncoating. In this approach, velocity gradient centrifugation is used to biochemically dissect the steps that initiate uncoating under defined conditions.

Acid-triggered molecular processes closely control cell entry of many viruses that enter through the endocytic system. In the case of influenza A virus ...

Imaging Cell Interaction in Tracheal Mucosa During Influenza Virus Infection Using Two-photon Intravital Microscopy

The analysis of cell-cell or cell-pathogen interaction in vivo is an important tool to understand the dynamics of the immune response to infection. Two-photon intravital microscopy (2P-IVM) allows the observation of cell interactions in deep tissue in living animals, while minimizing the photobleaching generated during image acquisition. To date, different models for 2P-IVM of lymphoid and non-lymphoid organs have been described. However, imaging of respiratory organs remains a challenge due to the movement associated with the breathing cycle of the animal.
Here, we describe a protocol to visualize in vivo immune cell interactions in the trachea of mice infected with influenza virus using 2P-IVM. To this purpose, we developed a custom imaging platform, which included the surgical exposure and intubation of the trachea, followed by the acquisition of dynamic images of neutrophils and dendritic cells (DC) in the mucosal epithelium. Additionally, we detailed the steps needed to perform influenza intranasal infection and flow cytometric analysis of immune cells in the trachea. Finally, we analyzed neutrophil and DC motility as well as their interactions during the course of a movie. This protocol allows for the generation of stable and bright 4D images necessary for the assessment of cell-cell interactions in the trachea.

In this study, we present a protocol to perform two-photon intravital imaging and cell interaction analysis in the murine tracheal mucosa after infection with influenza virus. This protocol will be relevant for researchers studying immune cell dynamics during respiratory infections.

The analysis of cell-cell or cell-pathogen interaction in vivo is an important tool to understand the dynamics of the immune response to infection. ...

A Luciferase-fluorescent Reporter Influenza Virus for Live Imaging and Quantification of Viral Infection

Influenza A viruses (IAVs) cause human respiratory disease that is associated with significant health and economic consequences. As with other viruses, studying IAV requires the use of laborious secondary approaches to detect the presence of the virus in infected cells and/or in animal models of infection. This limitation has been recently circumvented with the generation of recombinant IAVs expressing easily traceable fluorescent or bioluminescent (luciferase) reporter proteins. However, researchers have been forced to select fluorescent or luciferase reporter genes due to the restricted capacity of the IAV genome for including foreign sequences. To overcome this limitation, we have generated a recombinant replication-competent bi-reporter IAV (BIRFLU) stably expressing both a fluorescent and a luciferase reporter gene to easily track IAV infections in vitro and in vivo. To this end, the viral non-structural (NS) and hemagglutinin (HA) viral segments of influenza A/Puerto Rico/8/34 H1N1 (PR8) were modified to encode the fluorescent Venus and the bioluminescent Nanoluc luciferase proteins, respectively. Here, we describe the use of BIRFLU in a mouse model of IAV infection and the detection of both reporter genes using an in vivo imaging system. Notably, we have observed a good correlation between the expressions of both reporters and viral replication. The combination of cutting-edge techniques in molecular biology, animal research and imaging technologies, provides researchers the unique opportunity to use this tool for influenza research, including the study of virus-host interactions and dynamics of viral infections. Importantly, the feasibility to genetically alter the viral genome to express two foreign genes from different viral segments opens up opportunities to use this approach for: (i) the development of novel IAV vaccines, (ii) the generation of recombinant IAVs that can be used as vaccine vectors for the treatment of other human pathogen infections.

Influenza A viruses (IAVs) are contagious respiratory pathogens that cause annual epidemics and occasional pandemics. Here, we describe a protocol to track viral infections in vivo using a novel recombinant luciferase and fluorescence-expressing bi-reporter IAV (BIRFLU). This approach provides researchers with an excellent tool to study IAV in vivo.

Influenza A viruses (IAVs) cause human respiratory disease that is associated with significant health and economic consequences. As with other viruses, ...

Influenza A Virus Studies in a Mouse Model of Infection

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Chapters in this video

Using Bioluminescent Imaging to Investigate Synergism Between Streptococcus pneumoniae and Influenza A Virus in Infant Mice

Influenza Virus Propagation in Embryonated Chicken Eggs

Co-immunoprecipitation of the Mouse Mx1 Protein with the Influenza A Virus Nucleoprotein

Nasal Wipes for Influenza A Virus Detection and Isolation from Swine

Measuring Attachment and Internalization of Influenza A Virus in A549 Cells by Flow Cytometry

Neutrophil Isolation and Analysis to Determine their Role in Lymphoma Cell Sensitivity to Therapeutic Agents

A Miniaturized Glycan Microarray Assay for Assessing Avidity and Specificity of Influenza A Virus Hemagglutinins

In Vitro Disassembly of Influenza A Virus Capsids by Gradient Centrifugation

Imaging Cell Interaction in Tracheal Mucosa During Influenza Virus Infection Using Two-photon Intravital Microscopy

A Luciferase-fluorescent Reporter Influenza Virus for Live Imaging and Quantification of Viral Infection