Name: imaging cell interaction in tracheal mucosa during influenza virus infection using two-photon intravital microscopy
Uploaded: 2018-08-17T15:00:00
Description: Watch this Scientific Journal Video about Imaging Cell Interaction in Tracheal Mucosa During Influenza Virus Infection Using Two-photon Intravital Microscopy at JoVE.com

This work was supported by the Swiss National Foundation (SNF) grants (176124, 145038, and 148183), the European Commission Marie Curie Reintegration Grant (612742), and the SystemsX.ch for a grant to D.U.P. (2013/124).

All animal procedures involving mice were performed in accordance with the Swiss Federal Veterinary Office guidelines and animal protocols were approved by the local veterinarian authorities.
1. Influenza Infection of CD11c-YFP Mice
<ol>
	<li>Biosafety 
	NOTE: The mouse adapted strain of influenza A/Puerto Rico/8/34 H1N1 (PR8) was grown in fertilized eggs, purified and titrated as previously described21. All the steps involving infected animals o...

<ol>
	<li>Helmchen, F., Denk, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deep+tissue+two-photon+microscopy.">Deep tissue two-photon microscopy.</a> Nature Methods. 2 (12), 932-940 (2005).</li><li>Zipfel, W. R., Williams, R. M., Webb, W. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonlinear+magic:+multiphoton+microscopy+in+the+biosciences.">Nonlinear magic: multiphoton microscopy in the biosciences.</a> Nature biotechnology. 21 (11), 1369-1377 (2003).</li><li>Fein, M. R., Egeblad, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Caught+in+the+act:+revealing+the+metastatic+process+by+live+imaging.">Caught in the act: revealing the metastatic process by live imaging.</a> Disease Models &amp; Mechanisms. 6 (3), 580-593 (2013).</li><li>Dombeck, D. A., Harvey, C. D., Tian, L., Looger, L. L., Tank, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+imaging+of+hippocampal+place+cells+at+cellular+resolution+during+virtual+navigation.">Functional imaging of hippocampal place cells at cellular resolution during virtual navigation.</a> Nature Neuroscience. 13 (11), 1433-1440 (2010).</li><li>Cahalan, M. D., Parker, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Choreography+of+cell+motility+and+interaction+dynamics+imaged+by+two-photon+microscopy+in+lymphoid+organs.">Choreography of cell motility and interaction dynamics imaged by two-photon microscopy in lymphoid organs.</a> Annual review of immunology. 26, 585-626 (2008).</li><li>Germain, R. N., Robey, E. A., Cahalan, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Decade+of+Imaging+Cellular+Motility+and+Interaction+Dynamics+in+the+Immune+System.">A Decade of Imaging Cellular Motility and Interaction Dynamics in the Immune System.</a> Science. 336 (6089), 1676-1681 (2012).</li><li>Coombes, J. L., Robey, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+imaging+of+host-pathogen+interactions+in+vivo.">Dynamic imaging of host-pathogen interactions in vivo.</a> Nature Reviews Immunology. 10 (5), 353-364 (2010).</li><li>Pulendran, B., Maddur, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Innate+Immune+Sensing+and+Response+to+Influenza.">Innate Immune Sensing and Response to Influenza.</a> Life Science Journal. 6 (4), 23-71 (2014).</li><li>Lim, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+trails+guide+influenza-+specific+CD8+++T+cells+in+the+airways.">Neutrophil trails guide influenza- specific CD8 + T cells in the airways.</a> Science. 349 (6252), (2015).</li><li>Kim, J. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+imaging+of+tracheal+epithelial+cells+in+mice+during+airway+regeneration.">In vivo imaging of tracheal epithelial cells in mice during airway regeneration.</a> American journal of respiratory cell and molecular biology. 47 (6), 864-868 (2012).</li><li>Kretschmer, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autofluorescence+multiphoton+microscopy+for+visualization+of+tissue+morphology+and+cellular+dynamics+in+murine+and+human+airways.">Autofluorescence multiphoton microscopy for visualization of tissue morphology and cellular dynamics in murine and human airways.</a> Laboratory investigation; a journal of technical methods and pathology. 96 (8), 918-931 (2016).</li><li>Veres, T. Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intubation-free+in+vivo+imaging+of+the+tracheal+mucosa+using+two-photon+microscopy.">Intubation-free in vivo imaging of the tracheal mucosa using two-photon microscopy.</a> Scientific Reports. 7 (1), 694 (2017).</li><li>Looney, M. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stabilized+imaging+of+immune+surveillance+in+the+mouse+lung.">Stabilized imaging of immune surveillance in the mouse lung.</a> Nature. 8 (1), 91-96 (2011).</li><li>Thornton, E. E., Krummel, M. F., Looney, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live+Imaging+of+the+Lung.">Live Imaging of the Lung.</a> Current Protocols in Cytometry. 60 (1), (2012).</li><li>Tabuchi, A., Mertens, M., Kuppe, H., Pries, A. R., Kuebler, W. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intravital+microscopy+of+the+murine+pulmonary+microcirculation.">Intravital microscopy of the murine pulmonary microcirculation.</a> Journal of Applied Physiology. 104 (2), 338-346 (2008).</li><li>Fiole, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-photon+intravital+imaging+of+lungs+during+anthrax+infection+reveals+long-lasting+macrophage-dendritic+cell+contacts.">Two-photon intravital imaging of lungs during anthrax infection reveals long-lasting macrophage-dendritic cell contacts.</a> Infection and immunity. 82 (2), 864-872 (2014).</li><li>Secklehner, J., Lo Celso, C., Carlin, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intravital+microscopy+in+historic+and+contemporary+immunology.">Intravital microscopy in historic and contemporary immunology.</a> Immunology and Cell Biology. 95 (6), 506-513 (2017).</li><li>Lambrecht, B. N., Hammad, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lung+Dendritic+Cells+in+Respiratory+Viral+Infection+and+Asthma:+From+Protection+to+Immunopathology.">Lung Dendritic Cells in Respiratory Viral Infection and Asthma: From Protection to Immunopathology.</a> Annual Review of Immunology. 30 (1), 243-270 (2012).</li><li>Camp, J. V., Jonsson, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+role+for+neutrophils+in+viral+respiratory+disease.">A role for neutrophils in viral respiratory disease.</a> Frontiers in Immunology. 8, (2017).</li><li>van Gisbergen, K. P. J. M., Sanchez-Hernandez, M., Geijtenbeek, T. B. H., van Kooyk, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophils+mediate+immune+modulation+of+dendritic+cells+through+glycosylation-dependent+interactions+between+Mac-1+and+DC-SIGN.">Neutrophils mediate immune modulation of dendritic cells through glycosylation-dependent interactions between Mac-1 and DC-SIGN.</a> The Journal of experimental medicine. 201 (8), 1281-1292 (2005).</li><li>Gonzalez, S. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capture+of+influenza+by+medullary+dendritic+cells+via+SIGN-R1+is+essential+for+humoral+immunity+in+draining+lymph+nodes.">Capture of influenza by medullary dendritic cells via SIGN-R1 is essential for humoral immunity in draining lymph nodes.</a> Nature Immunology. 11 (5), 427-434 (2010).</li><li>Lindquist, R. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualizing+dendritic+cell+networks+in+vivo.">Visualizing dendritic cell networks in vivo.</a> Nature immunology. 5 (12), 1243-1250 (2004).</li><li>Li, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+V&#947;9V&#948;2-T+cells+efficiently+kill+influenza+virus-infected+lung+alveolar+epithelial+cells.">Human V&#947;9V&#948;2-T cells efficiently kill influenza virus-infected lung alveolar epithelial cells.</a> Cellular and Molecular Immunology. 10 (2), 159-164 (2013).</li><li>Tran Cao, H. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+the+transgenic+cyan+fluorescent+protein+(CFP)-expressing+nude+mouse+for+&amp;#34;technicolor&amp;#34;+cancer+imaging.">Development of the transgenic cyan fluorescent protein (CFP)-expressing nude mouse for &amp;#34;technicolor&amp;#34; cancer imaging.</a> Journal of Cellular Biochemistry. 107 (2), 328-334 (2009).</li><li>Jaber, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dose+regimens,+variability,+and+complications+associated+with+using+repeat-bolus+dosing+to+extend+a+surgical+plane+of+anesthesia+in+laboratory+mice.">Dose regimens, variability, and complications associated with using repeat-bolus dosing to extend a surgical plane of anesthesia in laboratory mice.</a> Journal of the American Association for Laboratory Animal Science JAALAS. 53 (6), 684-691 (2014).</li><li>Pizzagalli, D. U., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leukocyte+Tracking+Database,+a+collection+of+immune+cell+tracks+from+intravital+2-photon+microscopy+videos.">Leukocyte Tracking Database, a collection of immune cell tracks from intravital 2-photon microscopy videos.</a> Scientific Data. , (2018).</li><li>Sommer, C., Straehle, C., Kothe, U., Hamprecht, F. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ilastik:+Interactive+learning+and+segmentation+toolkit.">Ilastik: Interactive learning and segmentation toolkit.</a> 2011 IEEE International Symposium on Biomedical Imaging: From Nano to Macro. , 230-233 (2011).</li><li>Beltman, J. B., Mar&#233;e, A. F. M., De Boer, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysing+immune+cell+migration.">Analysing immune cell migration.</a> Nature Reviews Immunology. 9 (11), 789-798 (2009).</li><li>Keller, H. U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Motility,+cell+shape,+and+locomotion+of+neutrophil+granulocytes.">Motility, cell shape, and locomotion of neutrophil granulocytes.</a> Cell motility. 3 (1), 47-60 (1983).</li><li>Sumen, C., Mempel, T. R., Mazo, I. B., von Andrian, U. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intravital+Microscopy.">Intravital Microscopy.</a> Immunity. 21 (3), 315-329 (2004).</li><li>Lambert Emo, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live+Imaging+of+Influenza+Infection+of+the+Trachea+Reveals+Dynamic+Regulation+of+CD8++T+Cell+Motility+by+Antigen.">Live Imaging of Influenza Infection of the Trachea Reveals Dynamic Regulation of CD8+ T Cell Motility by Antigen.</a> PLOS Pathogens. 12 (9), e1005881 (2016).</li><li>Kjos, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bright+fluorescent+Streptococcus+pneumoniae+for+live-cell+imaging+of+host-pathogen+interactions.">Bright fluorescent Streptococcus pneumoniae for live-cell imaging of host-pathogen interactions.</a> Journal of bacteriology. 197 (5), 807-818 (2015).</li></ol>

This work presents a detailed protocol for the generation of 4D images showing the migration of adoptively transferred neutrophils and their interactions with DC during an influenza infection in the mouse trachea. The described 2P-IVM model will be relevant to study immune cell dynamics during an infection in the airways.
Recently, several models based on the visualization of cell dynamics in the airways have been developed9,10,</...

Two-photon intravital microscopy (2P-IVM) is an effective technique for real time imaging of cell-to-cell interactions as they occur in their natural environment1. One of the main advantages of this method is that it allows the study of cellular processes at a greater specimen depth (500 &#181;m to 1 mm) compared with other traditional imaging techniques2. At the same time, the use of two low-energy photons generated by the two-photon laser minimizes the tissue photo-damage typically associated with the image acquisition process2. During the last decade, 2P-IVM has been applied to study different types of cell-cell interactions in several disciplines3,4,5. These studies have been especially relevant to investigate immune cells, which are characterized by their high dynamism and the formation of prominent contacts following the signals generated by other cells and the environment. 2P-IVM has been also applied to study the interactions between pathogen and host6. Indeed, it has been previously shown that some pathogens can alter the type and duration of the contacts between immune cells, hampering, as a result, the immune response7.
The airway mucosa is the first site in which the immune response against airborne pathogens is generated8. Therefore, in vivo analysis of pathogen-host interactions in this tissue is critical to understand the initiation of the host defense mechanisms during infection. However, 2P-IVM of the airways is challenging mainly due to the artifacts produced by the breathing cycle of the animal, which compromises the process of image acquisition. Recently, different surgical models have been described for imaging murine trachea9,10,11,12 and lungs13,14,15,16. Tracheal 2P-IVM models represent an excellent set-up to visualize the initial phase of the immune reaction in the upper airways, while lung-alveoli 2P-IVM models are more suitable to study the late phase of infections. The developed lung models present a limitation associated with the presence of air-filled alveoli, which restrict the optical penetration of the laser and make the mucosal layer of the intrapulmonary airways inaccessible for in vivo imaging17. Conversely, the structure of the trachea, formed by a continuous epithelium, facilitates image acquisition.
Here, we present a protocol that includes a detailed description of the steps required to perform influenza infection, surgical preparation of the animals, and 2P-IVM of the trachea. In addition, we describe a specific experimental set-up for the visualization of neutrophils and dendritic cells (DC), two immune cell types that play an important role as mediators of the defense mechanism against influenza virus18,19. Finally, we describe a procedure to analyze neutrophil-DC interactions. These contacts have been shown to modulate DC activation and, subsequently, to affect the immune responses against pathogens20.

<table>
	<tbody>
		<tr>
			<td>Gigasept instru AF</td>
			<td>Sch&#252;lke &#38; Mayr GmbH</td>
			<td></td>
			<td>4% solution</td>
		</tr>
		<tr>
			<td>CD11c-YFP mice</td>
			<td>Jackson Laboratories</td>
			<td>008829</td>
			<td>mice were bred in-house</td>
		</tr>
		<tr>
			<td>CK6-ECFP mice</td>
			<td>Jackson Laboratories</td>
			<td>004218</td>
			<td>mice were bred in-house</td>
		</tr>
		<tr>
			<td>1 X Dulbecco&#39;s Phosphate Buffered Saline modified without Calcium Choride and Magnesium Chloride</td>
			<td>Sigma</td>
			<td>D8537-500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>10 X Dulbecco&#39;s Phosphate Buffered Saline modified without Calcium Choride and Magnesium Chloride</td>
			<td>Sigma</td>
			<td>D1408-500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Percoll PLUS</td>
			<td>Sigma</td>
			<td>E0414-1L</td>
			<td>Store at 4&#176;C</td>
		</tr>
		<tr>
			<td>Ketamin Labatec</td>
			<td>Labatec Pharma</td>
			<td>7680632310024</td>
			<td>Store at RT, store at 4&#176;C when in solution of ket/xyl mixture</td>
		</tr>
		<tr>
			<td>Rompun 2% (Xylazin)</td>
			<td>Bayer</td>
			<td>6293841.00.00</td>
			<td>Store at RT, store at 4&#176;C when in solution of ket/xyl mixture</td>
		</tr>
		<tr>
			<td>26 G 1 mL Sub-Q BD Plastipak</td>
			<td>BD Plastipak</td>
			<td>305501</td>
			<td></td>
		</tr>
		<tr>
			<td>30 G 0,3 mL BD Micro-Fine Insulin Syringes</td>
			<td>BD</td>
			<td>324826</td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon 40 &#181;m Cell Strainer</td>
			<td>Corning</td>
			<td>352340</td>
			<td></td>
		</tr>
		<tr>
			<td>2 mL Syringes</td>
			<td>BD Plastipak</td>
			<td>300185</td>
			<td></td>
		</tr>
		<tr>
			<td>Microlance 3 18 G needles</td>
			<td>BD</td>
			<td>304622</td>
			<td></td>
		</tr>
		<tr>
			<td>Introcan Safety 20G (catheter)</td>
			<td>Braun</td>
			<td>4251652.01</td>
			<td></td>
		</tr>
		<tr>
			<td>6 Well Cell Culture Cluster</td>
			<td>Costar</td>
			<td>3516</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI medium 1640 + HEPES (1X)</td>
			<td>ThermoFisher Scientific</td>
			<td>42401-018</td>
			<td>Store at 4&#176;C</td>
		</tr>
		<tr>
			<td>Liberase TL Research Grade</td>
			<td>Roche</td>
			<td>5401020001</td>
			<td>Store at -20&#176;C / collagenase (I and II) mixture</td>
		</tr>
		<tr>
			<td>DNAse I</td>
			<td>Amresco (VWR)</td>
			<td>0649-50KU</td>
			<td>Store at -20&#176;C</td>
		</tr>
		<tr>
			<td>CellTrace Violet stain</td>
			<td>ThermoFisher Scientific</td>
			<td>C34557</td>
			<td>Store at -20&#176;C</td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Sigma</td>
			<td>EDS-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Gibco</td>
			<td>10270-106</td>
			<td>Store at -20&#176;C</td>
		</tr>
		<tr>
			<td>PE-10 Micro Medical Tubing</td>
			<td>2Biological Instruments SNC</td>
			<td>#BB31695-PE/1</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical Plastic Tape</td>
			<td>M Plast</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Viscotears</td>
			<td>Bausch &#38; Lomb</td>
			<td></td>
			<td>Store at RT</td>
		</tr>
		<tr>
			<td>Plasticine</td>
			<td>Ohropax</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>High Tolerance Glass Coverslip 15mm Round</td>
			<td>Warner Instruments</td>
			<td>64-0733</td>
			<td></td>
		</tr>
		<tr>
			<td>SomnoSuite Portable Animal Anesthesia System</td>
			<td>Kent Scientific</td>
			<td>SS-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Nuvo Lite mark 5</td>
			<td>GCE medline</td>
			<td>14111211</td>
			<td></td>
		</tr>
		<tr>
			<td>MiniTag (gaseous anesthesia and heating bench)</td>
			<td>Tem Sega</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>SURGICAL BOARD</td>
			<td>University of Bern</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>TrimScope II Two-photon microscope</td>
			<td>LaVision Biotec</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Chameleon Vision Ti:Sa lasers</td>
			<td>Coherent Inc.</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>25X NA 1.05 water immersion objective</td>
			<td>Olympus</td>
			<td>XLPLN25XWMP2</td>
			<td></td>
		</tr>
		<tr>
			<td>The Cube&#38;The Box incubation chamber and temperature controller</td>
			<td>Life imaging Services</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Imaris 9.1.0</td>
			<td>Bitplane</td>
			<td></td>
			<td>Imaging software</td>
		</tr>
		<tr>
			<td>GraphPad Prism 7</td>
			<td>GraphPad</td>
			<td></td>
			<td>Statistical software</td>
		</tr>
	</tbody>
</table>

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 work, we described a detailed protocol to study in vivo the motility and the interactions between neutrophils and DC during influenza infection in murine trachea (Figure 3A). To this purpose, we isolated CFP+ neutrophils (92% purity; Figure 3B) from CK6-ECFP mice and we adoptively transferred them into a CD11c-YFP mouse infected with influenza. After that, we performed 2P-IVM of the trachea at day 3 p....

Watch this Scientific Journal Video about Imaging Cell Interaction in Tracheal Mucosa During Influenza Virus Infection Using Two-photon Intravital Microscopy at JoVE.com

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

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. ...

This method can help answer key questions in the study of immune responses to airborne pathogens about the dynamics of immune cells'interactions during respiratory infections. The main advantage of this technique is the ability to obtain bright and stable 4D images of the tracheal epithelium throughout the simple surgery. Though this method can provide insight into the neutrophil and the lytic cell interactions during influenza infection, it can also be applied to the study of different immune cells or airborne pathogens.Generally, individuals new to this method will struggle with maintaining a stable and minimal inflamed surgery. Moreover, image analysis can be tricky due to the presence of heart defects. For intranasal influenza infection, place an anesthetized six-to eight-week-old CD11c-YFP mouse in the supine position, and confirm deep sedation by lack of response to toe pinch.Placing the pipette close to the left nostril, dispense small droplets into the nasal cavity approximately 20 seconds apart, until the mouse has inhaled the entire 15 microliter volume of PR8 inoculate. After two to five minutes, deliver 15 microliters of virus into the right nostril in the same manner. When all of the inoculum has been delivered, confirm that the mouse is breathing normally, and place the animal in its cage in lateral decubitus with monitoring until full recovery.Three days post-infection, remove both femora and tibiae from a transgenic CFP-expressing mouse, and gently clean the bones with forceps. Cut the bone epiphysis and use a one-milliliter syringe equipped with a 26 gauge needle to flush the bone marrow from each bone with sterile cold PBS into a 50-milliliter tube on ice. When all of the bone marrow has been harvested, aspirate the marrow through the needle tip several times and filter the dissociated cell suspension through a 40-micrometer strainer.Collect the cells by centrifugation, and resuspend the pellet in two milliliters of cold PBS. Next, carefully layer two milliliters of each of three Percoll gradients in a 15-milliliter tube from most to least concentrated. Then carefully add two milliliters of bone marrow cell suspension onto the top gradient layer for centrifugal density gradient separation.At the end of the centrifugation, carefully remove the band from the 64 and 72%gradient interface and wash the neutrophils in cold PBS. Then resuspend the pellet in 100 microliters of fresh PBS on ice for counting, and resuspend the cells at a five times 10 to the sixth cells per 100 microliters of PBS concentration for intravenous injection into the inoculated CD11c-YFP recipient animals. 12 hours after adoptive transfer, place the anesthetized recipient animal on a customized surgical board over a 37-degree Celsius heated surface, and remove the hair from the neck of the mouse by shaving and a depilatory cream.Place the mouse above the plastic mouse positional with the head outside of the positional at an angle that facilitates intubation of the trachea, and secure the forelimbs, paws, and the tail with surgical tape. Apply ointment to the eyes and disinfect the exposed skin. Next, make a one-centimeter incision along the medial axis of the neck between the upper chest and the line passing through the lower point of the mandible, and laterally move the skin patches and the salivary glands to visualize the trachea.Use forceps to carefully dissect the trachea, intubate the mouse with a catheter, and immediately start the artificial ventilation. Use a surgical hook connected to a rod on the surgical board to fix the catheter height and orientation, and expose the trachea up to the chin. Encircle the trachea with petroleum jelly and hydrate the trachea with a few drops of warm PBS.Then glue a coverslip onto a metal holder, and screw the holder to the XYZ translator to allow the coverslip to be placed on top of the surgical preparation. It is very critical to properly expose and extend the trachea, and to lightly press it with the coverslip, to maintain the tissue stable long enough for the imaging. For time-lapse imaging in vivo, place the surgical board inside the 37-degree Celsius incubation chamber of the two-photon microscope, and add a drop of water to the coverslip.After centering the setup and focusing on the tracheal tissue, set the scanning frequency to 800 hertz with 520 by 520 pixels, a field of view of 440 by 440 micrometers, and a line average of one. Set the titanium sapphire lasers to the appropriate wavelength and power percentage according to the excitation fluorophores, and set up the 3D and time-lapse acquisition mode with simultaneous excitation. Then define a range of 50 micrometers along the z-axis with a step size of three micrometers, and record images every 30 seconds for 30 minutes.Following this experimental setup, stable 4D images can be captured in situ within the infected trachea over a 30-minute tracking period. Analysis of the 4D images reveals significant differences between dendritic cell and recruited neutrophil movement with a significantly faster speed demonstrated by the latter. The complex morphology of the dendritic cells causes frequent errors in cell tracking, which in turn produces tracks with a decreased duration and an increased variance in the measured directional behavior.Therefore, a robust metric was created for measuring the directionality by considering the track duration, revealing a significant difference in the directionality of neutrophils compared to dendritic cells. In addition, computation of the distance between the neutrophils and the dendritic cells allows the detection and analysis of their contacts over time, with some neutrophils in this representative experiment forming multiple brief contacts with dendritic cells and some not forming any contact with dendritic cells during the imaging period. Moreover, study of the average trend of the distance between neutrophils and dendritic cells over time facilitates the study of the overall positioning of the cells, while investigation of the trend in specific cells allows characterization of the behavior of each individual cell.Knowing this procedure, other methods like flow cytometry of the trachea can be performed to assess the quantification and characterization of different immune cells'recruitments in infected trachea. Don't forget that working with any influenza virus strain, even if mouse-adapted, can be hazardous, and that therefore, every procedure should be performed under biosafety level two conditions.

imaging-cell-interaction-tracheal-mucosa-during-influenza-virus

Research

JoVE Journal

Immunology and 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 ...

Intravital Imaging of the Mouse Thymus using 2-Photon Microscopy

Two-photon Microscopy (TPM) provides image acquisition in deep areas inside tissues and organs. In combination with the development of new stereotactic tools and surgical procedures, TPM becomes a powerful technique to identify "niches" inside organs and to document cellular "behaviors" in live animals. While intravital imaging provides information that best resembles the real cellular behavior inside the organ, it is both more laborious and technically demanding in terms of required equipment/procedures than alternative ex vivo imaging acquisition. Thus, we describe a surgical procedure and novel "stereotactic" organ holder that allows us to follow the movements of Foxp3+ cells within the thymus.
Foxp3 is the master regulator for the generation of regulatory T cells (Tregs). Moreover, these cells can be classified according to their origin: ie. thymus-differentiated Tregs are called "naturally-occurring Tregs" (nTregs), as opposed to peripherally-converted Tregs (pTregs). Although significant amount of research has been reported in the literature concerning the phenotype and physiology of these T cells, very little is known about their in vivo interactions with other cells. This deficiency may be due to the absence of techniques that would permit such observations. The protocol described in this paper provides a remedy for this situation.
Our protocol consists of using nude mice that lack an endogenous thymus since they have a punctual mutation in the DNA sequence that compromises the differentiation of some epithelial cells, including thymic epithelial cells. Nude mice were gamma-irradiated and reconstituted with bone marrows (BM) from Foxp3-KIgfp/gfp mice. After BM recovery (6 weeks), each animal received embryonic thymus transplantation inside the kidney capsule. After thymus acceptance (6 weeks), the animals were anesthetized; the kidney containing the transplanted thymus was exposed, fixed in our organ holder, and kept under physiological conditions for in vivo imaging by TPM. We have been using this approach to study the influence of drugs in the generation of regulatory T cells.

We have developed novel laboratory tools and protocols for intravital imaging acquisition of the thymus. Our technique should help in the identification of &#x201C;niches&#x201D; within the thymus where T cell development occurs.

Two-photon Microscopy (TPM) provides image acquisition in deep areas inside tissues and organs. In combination with the development of new stereotactic ...

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 ...

Long Term Intravital Multiphoton Microscopy Imaging of Immune Cells in Healthy and Diseased Liver Using CXCR6.Gfp Reporter Mice

Liver inflammation as a response to injury is a highly dynamic process involving the infiltration of distinct subtypes of leukocytes including monocytes, neutrophils, T cell subsets, B cells, natural killer (NK) and NKT cells. Intravital microscopy of the liver for monitoring immune cell migration is particularly challenging due to the high requirements regarding sample preparation and fixation, optical resolution and long-term animal survival. Yet, the dynamics of inflammatory processes as well as cellular interaction studies could provide critical information to better understand the initiation, progression and regression of inflammatory liver disease. Therefore, a highly sensitive and reliable method was established to study migration and cell-cell-interactions of different immune cells in mouse liver over long periods (about 6 hr) by intravital two-photon laser scanning microscopy (TPLSM) in combination with intensive care monitoring.
The method provided includes a gentle preparation and stable fixation of the liver with minimal perturbation of the organ; long term intravital imaging using multicolor multiphoton microscopy with virtually no photobleaching or phototoxic effects over a time period of up to 6 hr, allowing tracking of specific leukocyte subsets; and stable imaging conditions due to extensive monitoring of mouse vital parameters and stabilization of circulation, temperature and gas exchange.
To investigate lymphocyte migration upon liver inflammation CXCR6.gfp knock-in mice were subjected to intravital liver imaging under baseline conditions and after acute and chronic liver damage induced by intraperitoneal injection(s) of carbon tetrachloride (CCl4).
CXCR6 is a chemokine receptor expressed on lymphocytes, mainly on Natural Killer T (NKT)-, Natural Killer (NK)- and subsets of T lymphocytes such as CD4 T cells but also mucosal associated invariant (MAIT) T cells1. Following the migratory pattern and positioning of CXCR6.gfp+ immune cells allowed a detailed insight into their altered behavior upon liver injury and therefore their potential involvement in disease progression.

Stable intravital high-resolution imaging of immune cells in the liver is challenging. Here we provide a highly sensitive and reliable method to study migration and cell-cell-interactions of immune cells in mouse liver over long periods (about 6 hours) by intravital multiphoton laser scanning microscopy in combination with intensive care monitoring.

Liver inflammation as a response to injury is a highly dynamic process involving the infiltration of distinct subtypes of leukocytes including monocytes, ...

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 ...

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.

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 ...

Cell Membrane Repair Assay Using a Two-photon Laser Microscope

Numerous pathophysiological insults can cause damage to cell membranes and, when coupled with innate defects in cell membrane repair or integrity, can result in disease. Understanding the underlying molecular mechanisms surrounding cell membrane repair is, therefore, an important objective to the development of novel therapeutic strategies for diseases associated with dysfunctional cell membrane dynamics. Many in vitro and in vivo studies aimed at understanding cell membrane resealing in various disease contexts utilize two-photon laser ablation as a standard for determining functional outcomes following experimental treatments. In this assay, cell membranes are subjected to wounding with a two-photon laser, which causes the cell membrane to rupture and fluorescent dye to infiltrate the cell. The intensity of fluorescence within the cell can then be monitored to quantify the cell's ability to reseal itself. There are several alternative methods for assessing cell membrane response to injury, as well as great variation in the two-photon laser wounding approach itself, therefore, a single, unified model of cell wounding would beneficially serve to decrease the variation between these methodologies. In this article, we outline a simple two-photon laser wounding protocol for assessing cell membrane repair in vitro in both healthy and dysferlinopathy patient fibroblast cells transfected with or without a full-length dysferlin plasmid.

Cell membrane wounding via two-photon laser is a widely used method for assessing membrane resealing ability and can be applied to multiple cell types. Here, we describe a protocol for in vitro live-imaging of membrane resealing in dysferlinopathy patient cells following two-photon laser ablation.

Numerous pathophysiological insults can cause damage to cell membranes and, when coupled with innate defects in cell membrane repair or integrity, can ...

Two-photon Intravital Imaging of Leukocytes During the Immune Response in Lipopolysaccharide-treated Mouse Liver

Sepsis is a type of severe infection that can cause organ failure and tissue damage. Although the mortality and morbidity rates associated with sepsis are extremely high, no direct treatment or organ-related mechanism has been examined in detail in real time. The liver is the key organ that manages toxins and infections in the human body. Herein, we aimed to perform intravital imaging of mouse liver after induction of endotoxemia in order to track the motility of immune cells, such as neutrophils and liver capsular macrophages (LCMs). Accordingly, we designed a novel surgical method for exposure of the liver with minimally invasive surgery. Mice were intraperitoneally injected with lipopolysaccharide (LPS), a common endotoxin. Using our novel surgical approach for exposure and intravital imaging of the mouse liver, we found that neutrophil recruitment in LPS-treated LysM-green fluorescent protein (GFP) mouse liver was increased compared with that in phosphate-buffered saline-treated liver. After LPS treatment, the number of neutrophils increased significantly with time. Additionally, using CX3Cr1-GFP mice, we successfully visualized liver resident macrophages called LCMs. Therefore, to investigate the efficacy of new reagents to control immune mobility in vivo, determining the motility and morphology of neutrophils and LCMs in the liver may allow us to identify therapeutic effect in organ failure and tissue damage caused by leukocytes activation in sepsis.

We established a novel surgical protocol for two-photon imaging of live mice liver with minimal invasion. With this technique, we identified the detailed structure of the liver during lipopolysaccharide-induced endotoxemia. We anticipate that this method may be utilized to determine the effectiveness of various reagents treatment to hepatic leukocyte migration.

Sepsis is a type of severe infection that can cause organ failure and tissue damage. Although the mortality and morbidity rates associated with sepsis are ...

Establishment of Viral Infection and Analysis of Host-Virus Interaction in Drosophila Melanogaster

Virus spreading is a major cause of epidemic diseases. Thus, understanding the interaction between the virus and the host is very important to extend our knowledge of prevention and treatment of viral infection. The fruit fly Drosophila melanogaster has proven to be one of the most efficient and productive model organisms to screen for antiviral factors and investigate virus-host interaction, due to powerful genetic tools and highly conserved innate immune signaling pathways. The procedure described here demonstrates a nano-injection method to establish viral infection and induce systemic antiviral responses in adult flies. The precise control of the viral injection dose in this method enables high experimental reproducibility. Protocols described in this study include the preparation of flies and the virus, the injection method, survival rate analysis, the virus load measurement, and an antiviral pathway assessment. The influence effects of viral infection by the flies' background were mentioned here. This infection method is easy to perform and quantitatively repeatable; it can be applied to screen for host/viral factors involved in virus-host interaction and to dissect the crosstalk between innate immune signaling and other biological pathways in response to viral infection.

Establishment of Viral Infection and Analysis of Host-Virus Interaction in Drosophila Melanogaster

This protocol describes how to establish viral infection in vivo in Drosophila melanogaster using the nano-injection method and basic techniques to analyze virus-host interaction.

Virus spreading is a major cause of epidemic diseases. Thus, understanding the interaction between the virus and the host is very important to extend our ...

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, ...