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).

<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>

The authors have nothing to disclose.

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 developed9,10,11,12,13,14,15,16. However, in vivo imaging of the lung is still challenging, considering the anatomic position of this organ and the technical difficulties to minimize the movement during the breathing cycle30. To overcome these problems, some authors have proposed the use of a custom-built circular suction chamber, which needs to be surgically inserted in the thorax13,14. However, this procedure requires an invasive intervention that could compromise the results, especially in those studies that have focused on the investigation of the inflammatory response. Furthermore, lung surgical models present a limitation for deep tissue imaging due to the light refraction originated by the air in the alveoli17. Conversely, different tracheal models have been recently employed to study cell dynamics in the airway epithelium. Imaging of this organ presents clear advantages compared to lung, such as the relatively simple surgery required to expose and immobilize the organ, as well as the higher accessibility to the tracheal epithelium. The proposed tracheal model is also relevant to investigate the initiation of the response against airway pathogens, such as influenza virus, since the trachea is one of the first sites of viral replication during the course of an influenza infection8.
Interestingly, a study showing an alternative intubation-free method for imaging the trachea has been recently published12. This method is characterized by a decreased inflammation and shows clear advantages in studies where the mucociliarity function of the epithelial cells needs to be preserved. However, this method does not guarantee sufficient stability and the acquisition of brighter signals necessary to study cell-cell contacts in a range of a few &#181;m. Conversely, the method presented in the current protocol provides better immobilization of the organ thanks to the intubation, and allows the detection of stronger fluorescence signals as a result of the shorter distance between the organ and the coverslip12.
Accomplishing tissue immobilization during in vivo 2P-IVM image acquisition is the most critical step to generate optimal data. Some crucial measures that contribute to the stability of the presented method include: an appropriate mouse anesthesia; a correct mouse intubation; and a surgical exposition of the trachea that allows an easy access to the organ by the coverslip. Additionally, imaging the right number of cells (ideally 30 cells per field of view) will strengthen the obtained results. The recruitment of the optimal number of cells will depend to a large extent on the viral infection dose, which is very much influenced by the proper administration of the viral inoculum.
Another critical step of the protocol is the surgical exposition of the trachea. Different measures can be adopted to minimize the damage caused to the organ during surgery. For example, the trachea should not be directly touched with surgical tools. Instead, it should be exposed by manipulating only the surrounding tissues (skin, salivary glands, and muscles). If strictly necessary, the trachea should be handled using unsharpened items. Additionally, efforts should be done to avoid blood vessel damage. Finally, to prevent organ dehydration, it is also important to cover it with PBS immediately after surgery.
Despite the unique advantages of this method over the previously described methods for the visualization of the immune cell interactions in the tracheal mucosa, the use of this model presents some limitations. As described above, the presence of inflammation associated with the tracheal surgery might represent a drawback when studying immune responses. To overcome this limitation, it is possible to administer anti-inflammatory drugs prior to the initiation of the procedure. Another limitation of this model is related to the presence of a strong autofluorescence signal existing in the airways, which is mainly generated by the resident cells and the mucus layer. This non-specific fluorescence creates artefacts that might hinder the analysis. Furthermore, misleading calculation of the track straightness parameter might be generated when comparing cell tracks of different durations and when tracking errors introduce tracks of short duration26. To overcome this problem, we applied a penalty coefficient to correct track straightness. Such correction is intended to minimize the effect of miss-tracking in the results28.
A crucial aspect of 2P-IVM experiments is the possibility to re-use mice that have undergone surgery and imaging. The in vivo imaging protocol described here does not require animal euthanasia or organ collection, thus leaving the possibility to recover and re-use mice after surgery for other procedures. Using a single mouse, for example, to perform trachea imaging at different time points could dramatically decrease the number of total animals needed in an experiment, supporting the animal reduction principle. Moreover, it could also reduce inter-individual variability. However, animal recovery and re-use must follow animal welfare standards that includes the administration of proper analgesic drugs and antibiotics to the animals during recovery time. All these procedures must be included in the animal experimentation protocol and approved by the local veterinarian authorities.
The described protocol can be easily adapted to the study of other immune cell types. For example, isolation and injection of (fluorescent or stained) pathogen-specific T cells might be used to study T cell activation dynamics31 as well as their interaction with other cells such as tracheal DC. In a similar way, the visualization of blood or lymphatic vessels could represent an interesting approach to study the recruitment of inflammatory cells into the tracheal tissue during the course of infection. Moreover, 2P-IVM of the trachea could also be applied to study the dynamics of the immune response to other airborne pathogens. Therefore, the use of transgenic fluorescent airborne pathogens, such as Streptococcus pneumoniae32, will create new opportunities to study their interactions with the immune system. Although this procedure focuses on measuring the dynamics of immune cells during infection, it could be also applied to different fields including cancer, asthma, or wound-healing.

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.i. At this time point we observed a clear recruitment of neutrophils in the infected area, as shown by flow cytometric analysis (Figure 3C). The 2P-IVM protocol requires the use of a specific surgical board and an oxygen supplier for rodents (Figure 1A). Supplying oxygen through a cannula inserted in the trachea helped the animal breathing, facilitated the exposition of the trachea, and controlled the organ movement associated with breathing (Figure 1B). Following this experimental set-up, we acquired stable 4D images in vivo in the infected trachea during a period of 30 min (Figure 3D, Movie 1).
The analysis of the acquired 4D images through specialized imaging software allowed to measure the migration of cells and to quantify the spatio-temporal dynamics of neutrophils and DC. Regarding cell motility, we observed significant differences between the movement of DC and the recruited neutrophils, which showed a significantly faster speed than the latter (Figure 4A). This result confirms the dynamic nature of neutrophils, previously described as highly motile cells capable of migrating towards a chemoattractant source29. Regarding directionality, we concluded that complex morphology of the DC yielded frequent errors in cell tracking, which in turn produced tracks with decreased duration and increased variance of the measured directional behavior (Figure 4B). For this reason, we computed a robust metric that is able to measure directionality by considering track duration. Using this metric, we observed a significant difference in the directionality of neutrophils vs DC (Figure 4C).
Additionally, the computation of the distance between neutrophils and DC allowed to detect and to analyze their contacts over time. In this experimental model, we observed some neutrophils that formed multiple-brief contacts with DC and others that did not form any contact during the imaged period (Figure 4D). Moreover, the study of the average trend of the distance between neutrophils and DC over time allowed us to study the overall positioning of the studied cells (Figure 4E), while the investigation of the trend in specific cells allowed to characterize the behavior of each single-cell (Figure 4F, Movie 2).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58355/58355fig1.jpg" /> 
Figure 1: Equipment and steps for 2P-IVM of murine trachea. (Ai) The portable animal anesthesia system in charge of the automated ventilation is connected to a pump that supplies oxygen to the mouse. Front view (Aii) and side view (Aiii) of the custom-made surgical board used for the tracheal model. The board is composed of a metal stage with a plastic mouse positional (Aii-a), a rod for holding a movable clamp (Aii-b), and a fine tunable XYZ translator (Aii-c). (B) Sequential steps of the tracheal surgical model: (Bi) hair removal of the surgical area, (Bii) positioning of the anesthetized mouse in the surgical board, (Biii) surgical exposition of the trachea, (Biv) intubation with a catheter with artificial ventilation, (Bv) fixation of the catheter, (Bvi) addition of PBS to the exposed trachea, (Bvii) mounting of the coverslip, and (Bviii) placement of a catheter with anesthesia. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58355/58355fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58355/58355fig2.jpg" /> 
Figure 2: Fluorescent signal detection during 2P-IVM. (A) Schematic representation of the microscope detection filter set-up and corresponding channels. Dichroic mirror at 560 nm separates blue/green from red/far red emissions. Additional dichroic mirror at 495 nm is used to further recognize the different subregions of the emission spectrum. Channel 1 employs a hybrid detector (emission filter 475/50), while channel 2 uses high sensitivity GaAsP PMT (emission filter 525/50). (B) Representative scatter dot plots of 2P signals showing the gating strategy for the generation of the colocalization channels for the identification of signal coming from the CFP (Bi) and the YFP (Bii) fluorophores. (Biii) Representative micrographs showing the specific signals from channel 1 (Ch 1, dark blue), channel 2 (Ch 2, green), the co-localization channel for CFP (light blue), the co-localization channel for YFP (yellow), and the combination of all channels (Ch 1+Ch 2+CFP+YFP). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58355/58355fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/58355/58355fig3.jpg" /> 
Figure 3: Intravital 4D imaging of neutrophils and DC in an influenza infected trachea. (A) Schematic outline of the protocol. (B) Representative flow cytometric scatterplot showing the percentage of neutrophils with respect to the total CD45+ cells in a cell suspension isolated from murine bone marrow using the Percoll gradient method. (C) Representative flow cytometric scatterplots showing an increase in the frequency of neutrophils in tracheas from uninfected mice compared to mice infected with influenza virus at day 3 p.i. (D) (Left panel) Anatomical image of a murine trachea showing the area selected for image acquisition. (Right panel) Representative 3D projection of a 2P-IVM micrograph showing the surface reconstruction of neutrophils (light blue) and DC (yellow) together with their tracks at day 3 p.i. SHG signal is shown in dark blue. Scale bar = 100 &#181;m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58355/58355fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/58355/58355fig4.jpg" /> 
Figure 4: Characterization of neutrophil and DC migration and interaction dynamics in influenza infected trachea. Representative plots showing the track speed mean (A), track straightness (B), and corrected track straightness (C), as defined by Beltman and colleagues (2009)28, of neutrophils and DC in trachea at day 3 p.i. with influenza virus. The corrected track straightness measurement exhibits robustness to tracking errors. (D) 2D histogram showing the frequency of neutrophil according to their number of contacts with DC and the mean contact duration. (E) Average distance of neutrophils to the closest DC during the duration of the movie. (F) (Left) Analysis of the distance of a representative neutrophil to the closest DC in time. The dotted red line indicates the distance threshold to consider that a neutrophil established a contact with a DC. (Right i-iii) Micrographs acquired at different time points representing the migration of a neutrophil (light blue) towards a DC (yellow). Cell tracks are shown as a multicolored line that changes color from blue to red to represent time. SHG signal from fibrillary collagen is shown in dark blue. Scale bar = 50 &#181;m. In all figures, the presented data are representative of at least three independent experiments. Results are given as mean &#177; SD. Statistics by Welch&#39;s test. ns p &#62;0.05; ****p &#60;0.0001. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58355/58355fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Movie 1" src="/files/ftp_upload/58355/58355movie1.jpg" /> 
Movie 1: Neutrophils and DC dynamics in trachea during influenza infection. 30 min time-lapse 3D image showing interaction dynamics between neutrophils (light blue) and DC (yellow) as well as their respective tracks with respect to the collagen network (dark blue) of the trachea. Representative neutrophil-DC interactions are indicated by white arrows. Cell tracks are shown as a multicolored line that changes color from blue to red to represent time. Scale bar = 50 &#181;m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58355/Movie1_rev.mp4" target="_blank">Please click here to view this video. (Right-click to download.)</a>
<img alt="Movie 2" src="/files/ftp_upload/58355/58355movie2.jpg" /> 
Movie 2: Representative short-term neutrophil-DC interaction in the trachea during influenza infection. 30 min time-lapse 3D image showing a representative interaction between a neutrophil (light blue) and a DC (yellow) and their respective tracks. Cell tracks are shown as a multicolored line that changes color from blue to red to represent time. SHG signal from collagen is shown in dark blue. Scale bar = 10 &#181;m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58355/Movie2_rev.mp4" target="_blank">Please click here to view this video. (Right-click to download.)</a>

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. ...

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

Nanyang Technological University

Research

JoVE Journal

Immunology and Infection

8.2K Views.  Università della Svizzera italiana (USI). 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.

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

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 ...

Highly Resolved Intravital Striped-illumination Microscopy of Germinal Centers

Monitoring cellular communication by intravital deep-tissue multi-photon microscopy is the key for understanding the fate of immune cells within thick tissue samples and organs in health and disease. By controlling the scanning pattern in multi-photon microscopy and applying appropriate numerical algorithms, we developed a striped-illumination approach, which enabled us to achieve 3-fold better axial resolution and improved signal-to-noise ratio, i.e. contrast, in more than 100 &#181;m tissue depth within highly scattering tissue of lymphoid organs as compared to standard multi-photon microscopy. The acquisition speed as well as photobleaching and photodamage effects were similar to standard photo-multiplier-based technique, whereas the imaging depth was slightly lower due to the use of field detectors. By using the striped-illumination approach, we are able to observe the dynamics of immune complex deposits on secondary follicular dendritic cells &#8211; on the level of a few protein molecules in germinal centers.

High-resolution intravital imaging with enhanced contrast up to 120 &#181;m depth in lymph nodes of adult mice is achieved by spatially modulating the excitation pattern of a multi-focal two-photon microscope. In 100 &#181;m depth we measured resolutions of 487 nm (lateral) and 551 nm (axial), thus circumventing scattering and diffraction limits.

Monitoring cellular communication by intravital deep-tissue multi-photon microscopy is the key for understanding the fate of immune cells within thick ...

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 ...