This work was supported by EMBO (to Y.E.), Foundation Machaon (to Y.E.) and SNSF (to B.A.I.). We thank the Bioimaging Core Facility for the availability of the Nikon A1r microscope and technical assistance. We thank Mrs. Clarissa Bartley for English correction.

NOTE: Animal procedures were performed in accordance with the Institutional Ethical Committee of Animal Care in Geneva, Switzerland and the Cantonal Veterinary Office. Authorization number GE/63/14.
1. Preparation of a Single Cell Suspension from Bone Marrow
<ol>
	<li>Sacrifice mouse (8-12 week old) by cervical dislocation. Sterilize hind legs with 70% ethanol. Remove skin from hind legs.</li>
	<li>Dissect out mouse femurs and tibias and remove tissue from legs with a scalpel. Rinse legs with 90% ethanol and place into a culture dish filled with PBS.</li>
	<li>Under the culture hood, clean tissue from femurs and tibias with a scalpel and separate at knee joint. Cut off each end of the bones.</li>
	<li>Flush bone marrow from each bone using a 23G needle and a 1 ml syringe filled with preparation medium (phenol red-free DMEM/F12, 1% rat serum), into a 50 ml screw tube. Disrupt cell aggregates by delicately passaging through the 23G needle and a 1 ml syringe. Bring total volume to 25 ml with preparation medium.</li>
	<li>Centrifuge 250 x g, 5 min, 4 &#176;C. Discard supernatant. Resuspend pellet in 1 ml Red Blood Cell Lysis RBLC buffer (8.3 g NH4Cl, 1 g NaHCO3, 1 ml EDTA (100 mM), complete to 1 L with distilled water, filter 0.22 &#181;m) in a 15 ml screw tube. Incubate 30 sec&#160;on ice.</li>
	<li>Add 10 ml of preparation medium and centrifuge 250 x g, 5 min, 4 &#176;C. Discard supernatant and resuspend in 2 ml preparation medium.</li>
</ol>
2. Neutrophil Enrichment by Negative Selection
<ol>
	<li>Add 150 &#181;l of Mouse neutrophil enrichment cocktail (cell isolation platform kit such as EasySep). Mix and incubate on ice for 10 min.</li>
	<li>Add 10 ml of phenol red free DMEM. Invert once and centrifuge 250 x g, 3 min, 4 &#176;C.</li>
	<li>Discard supernatant. Resuspend pellet in 1.75 ml preparation medium in 5 ml polystyrene round bottom tubes. Add 250 &#181;l Biotin Selection Cocktail. Mix and incubate on ice for 10 min.</li>
	<li>Vortex the magnetic particles (from the cell isolation platform kit) for 30 sec to resuspend particles. Add 500 &#181;l magnetic particles to cell suspension. Mix and incubate on ice for 10 min.</li>
	<li>Place the tube into the magnet. Wait 3 min.</li>
	<li>Invert the magnet onto a new 5 ml polystyrene round bottom tubes to collect the desired unlabeled cells. Do not take the last drop hanging in the tube. Unwanted cells will remain in the tube inside the magnet. Discard this tube into a biohazard waste.</li>
	<li>Place the new tube into the magnet. Wait 3 min.</li>
	<li>Invert the magnet onto a new 15 ml screw tube to collect the desired unlabeled cells. Do not take the last drop hanging in the tube.</li>
	<li>Complete volume to 5 ml with phenol red free DMEM.</li>
</ol>
3. Labeling of Neutrophils
<ol>
	<li>Add 0.5 &#181;l of an orange dye such as Cell Tracker Orange (working concentration 1 &#181;M, CMRA &#8211; chloromethyl-rodol-acetate, stock 10 mM in DMSO). Incubate 2 min at 37 &#176;C.</li>
	<li>Add 2.5 ml of preparation medium. Centrifuge 250 x g, 5 min, 4 &#176;C.</li>
	<li>Discard supernatant. Resuspend pellet in 1 ml preparation medium in a 1.5 ml tube.</li>
	<li>Take an aliquot to count with hematocytometer.</li>
	<li>Incubate 5 min at 37 &#176;C. Centrifuge 250 x g, 5 min, 4 &#176;C.</li>
	<li>Discard supernatant. Resuspend pellet in 1 ml PBS. Centrifuge 250 x g, 5 min, 4 &#176;C to wash.</li>
	<li>Discard supernatant. Resuspend pellet as 10x106 cells per 100 &#181;l PBS. Keep on ice until i.v. injection. NOTE: cells have to be i.v. injected as quickly as possible. 6-12x106 neutrophils/mouse are usually obtained.</li>
</ol>
4. Mouse Preparation for Intravital Microscopy
NOTE: Step 4.1.) and 4.2.) should be performed at the beginning of the experiment to avoid extended waiting time of labeled neutrophils on ice.
<ol>
	<li>Weigh the CX3CR1gfp mouse (8-12 week old).</li>
	<li>Prepare 800 &#181;l of anesthetics (ketamine 60 mg/kg, xylazine 4.5 mg/kg, acepromazone 1.75 mg/kg in PBS).</li>
	<li>Anesthetize mouse. Injection i.p. with 200 &#181;l / 20 g of mouse. Control anesthesia by toe pinching and by checking the respiratory rate.</li>
	<li>Inject neutrophils (10x106 cells in 100 &#181;l PBS) intravenously using the lateral tail veins or the retro-orbital sinus, at the convenience of the experimenter.</li>
	<li>Put the mouse on heating pad and protect the eyes with ocular gel.</li>
	<li>A glass coverslip (35 mm diameter) is put in a 10 cm tissue culture dish, which has a 30 mm diameter hole. Use oil is to maintain the tissue culture dish in contact with the coverslip.</li>
	<li>Incise abdominal skin with scissors to expose the peritoneum. Incise peritoneum with scissors to expose intestine.</li>
	<li>Add 200 &#181;l PBS (pre-heated at 37 &#176;C) into the peritoneal cavity. Take the mouse in your hand and turn it face down, so that the intestine gets out of the peritoneal cavity with a gentle pressure. Place the mouse in the tissue culture dish.</li>
	<li>Gently deroll the intestine with sterilized cotton buds onto the coverslip in order to expose the mesenteric vessels.</li>
	<li>Cut paper tissues in bands and wet them with 37&#176;C heated PBS. Immobilize the intestine with the pieces of paper tissues to decrease the movements resulting from peristalsis.</li>
	<li>Put the tissue culture dish and the mouse inside the 37 &#176;C thermostated chamber onto the custom-made tray stage of the inverted microscope. Introduce a syringe containing anesthetics s.c. into the hind leg. NOTE: Additionally, the mouse can receive oxygen (0.5 L/min) with a mask.</li>
	<li>Control mouse for anesthesia by toe pinching and checking the respiratory rate every 30 min. If needed, deliver a boost of anesthetics (20 &#181;l) to properly maintain anesthesia. NOTE: Drying of the vasculature should be avoided. Therefore, its humidity is maintained by regularly wetting the paper tissues used to immobilize the intestine with 37&#176;C-warmed PBS.</li>
</ol>
5. Measuring Neutrophil and Monocyte Behavior in Inflamed Vessels In Vivo using Intravital Microscopy
<ol>
	<li>Set lasers to 488- and 561- at the lowest power necessary to avoid laser-induced phototoxicity. In our experiments, it is lower than 0.5%. Intensity of GFP in monocytes and orange dye in neutrophils is so bright that usually 0.3% is enough. NOTE: This represents a laser power of 0.15 to 0.25 mW with our system.</li>
	<li>Acquire images of 512 x 512 pixels (i.e., 635 &#181;m) in 2.2 sec&#160;with an open pinhole using the 20X dry objective of the inverted microscope. Use a z-depth between 10 to 20 &#956;m, that ensures sufficient signal with the low laser powers. 
	NOTE: We usually perform experiments with a z-depth between 12 to 16 &#956;m. In the case of presented figures and movies, the z-depth is 20 &#956;m. Phase contrast allows the identification of endothelial walls and imaging is performed on mesenteric veins.&#160;Since patrolling cells move quite slowly with a speed of 5-10 &#181;m /min 6, recording a field of interest every 20 sec&#160;is satisfactory. With the described settings, the motorized stage allows the recording of up to 7 fields of interest at the same time.</li>
	<li>Place the mouse and the mesenteric vessels in the thermostat chamber of the microscope are allow them to recover from the preparation for 30 min&#160;before the acquisition of the first movie. During this time, choose several fields of interest. Focus on the luminal surface of the vessel closest to the objective. If needed, take advantage of the slight auto-fluorescence of endothelium to set the focus. 
	NOTE: Surgery during mouse preparation slightly stresses the endothelium. Consequently, rolling of neutrophils and/or monocytes can be observed in the first 15 min&#160;following mouse preparation.</li>
	<li>Record a first movie for 30 min&#160;under steady state conditions, one image every 20 sec. 
	NOTE: The software acquires each field of interest in 2.2 sec&#160;and the motorized stage automatically moves from one field to the other. It goes back to the first position within 20 sec&#160;during the 30 min&#160;of the recording movie.</li>
	<li>To initiate blood vessel inflammation, add a drop of 20 &#181;l of PBS containing 100 &#181;g of TLR2/TLR1 agonist Pam3CSK4 12 directly onto the imaged vessels.</li>
	<li>Control the focus for each field of interest. 
	NOTE: During the course of acquisition, there is always slight changes of focus on z-axis. Despite the 10-20 &#956;m z-depth, this can result in a decrease of fluorescence intensity. Therefore, manually refocus each field of interest at the end of each movie, if needed. Record movies for 30 min-periods and up to 3 hr total after initiation of inflammation.</li>
	<li>At the end of the experiment, sacrifice anesthetized mouse by cervical dislocation.</li>
</ol>
6. Generation of Movie Files and Tracking of Leukocytes
NOTE: The Nikon acquisition software generates .nd2 files but the following procedure would be similar with other software and brands.
<ol>
	<li>Export files as tiff series.</li>
	<li>Go to ImageJ software (<a href="http://rsb.info.nih.gov/ij/">http://rsb.info.nih.gov/ij/</a>). Import the tiff series. Each channel as a different file.</li>
	<li>Apply a median filter with a radius of 2.0 pixel for the green and red channels to reduce background noise (Process &#62; Filters &#62; Median&#8230;).</li>
	<li>Convert files into binary (Process &#62; Binary &#62; Make Binary). Enable the software to calculate the threshold for each image.</li>
	<li>Merge channels into one image series (Image &#62; Color &#62; Merge Channels&#8230;). Select the monocytes in the green channel, the neutrophils in the red channel and the transmitted light in the grey channel.</li>
	<li>Convert stacked images into RGB colors (Image &#62; Color &#62; Stack to RGB).</li>
	<li>Save file as .avi</li>
	<li>Data are imported and compiled in Imaris software (Bitplane). Movements of monocytes and neutrophils are then tracked using the Spot Tracking Wizard.</li>
</ol>

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The authors declare that they have no competing financial interests.

The methodologies described in this manuscript provide a consistent approach to efficiently study monocyte and neutrophil behavior in mesenteric veins under steady state and inflammatory conditions.
The crucial step of the preparation is the immobilization of the intestine with PBS-wetted tissues. If performed properly, mesenteric vessels are nicely exposed on the coverslip for image acquisition. This enables the selection of several fields of interest to monitor leukocyte behavior in mesenter...

Neutrophils and monocytes are cells of the innate immune system that continuously circulate in the blood. Upon injury or infection, inflammatory signals induce leucocyte diapedesis into damaged and infected tissues, herein initiating a cellular immune response 1-3. The rapidity of leukocyte mobilization determines the positive outcome of the immune responses. These intricate processes rely on specific molecules (e.g., selectins, endothelium-bound chemokines) present on the inflamed endothelium that help for the establishment of adhesive contacts between circulating leukocytes and the endothelium 1-3.To get insights on the molecules implicated in the leukocyte recruitment cascade, it is important to visualize the kinetics of cell recruitment and to track the behavior of each cell/population. An effective method involves intravital microscopy on transgenic mice expressing fluorescent proteins in cells of interest.
To date, several approaches using intravital microscopy were developed to image the vasculature 4,5. For instance, imaging of ear dermis vasculature or mesenteric veins by intravital confocal microscopy was used to identify the patrolling behavior of murine Ly6Clow monocytes and human CD14dimCD16+ monocytes on the luminal side of blood vessels under steady state conditions 6-8. The mouse cremaster vasculature model is often used to monitor the behavior of neutrophils or inflammatory Ly6Chigh monocytes under inflammatory or ischemic conditions in transgenic mice. In that case, cremaster is stimulated via intrascrotal injection of IL1&#946;, CCL2, TNF&#946; or fMLP. After 2-4 hr, tissues are then surgically exteriorized and analyzed by intravital confocal microscopy 9-11.
The following protocol describes a method to monitor monocytes and neutrophils at the same time with any inverted fluorescence confocal microscope. Furthermore, our method details how to image the same vessel before (steady state condition) and after inflammation and how to follow the kinetics of leukocyte recruitment. To this purpose, we use the CX3CR1gfp/wt mouse, whose monocytes express eGFP, i.v. injected with an orange dye-labeled murine neutrophils. Using an inverted confocal microscope, it is possible (1) to track and analyze the patrolling Ly6Clow monocytes under steady state conditions and (2) to follow the recruitment of both monocytes and neutrophils in the same vessel after local inflammation. Here we create the inflammatory conditions by using the TLR2/TLR1 agonist Pam3CSK4 12. Moreover, such imaging may help to determine the role of specific molecules of interest in the various steps of the leukocyte recruitment cascade if performed on specific knock-out mice or in presence of blocking antibodies 6,9,13.

<table><tbody><tr><td>5 ml polystyrene round bottom tubes&amp;nbsp;</td><td>Beckton Dickinson</td><td>352058</td><td></td></tr><tr><td>10x CFI Plan Apochromat 0.45&amp;nbsp;&amp;nbsp; DT:4mm&amp;nbsp;</td><td>Nikon</td><td></td><td></td></tr><tr><td>20x CFI Plan Apochromat VC 0.75 DT:1mm&amp;nbsp;</td><td>Nikon</td><td></td><td></td></tr><tr><td>Cell Tracker Orange CMRA Dye</td><td>Life Technologies</td><td>C34551</td><td></td></tr><tr><td>EasySep Magnet</td><td>Stem Cell Technologies</td><td>18000</td><td></td></tr><tr><td>EasySep Mouse Neutrophil Enrichement kit</td><td>Stem Cell Technologies</td><td>19762</td><td></td></tr><tr><td>EDTA</td><td>Sigma Aldrich</td><td>E6758</td><td></td></tr><tr><td>FCS</td><td>PAA</td><td>A15-042</td><td></td></tr><tr><td>Immersion Oil Type A</td><td>Nikon</td><td></td><td>any viscous oil&amp;nbsp;</td></tr><tr><td>Life Box Temperature Control System</td><td>Life Imaging</td><td></td><td></td></tr><tr><td>NaHCO3</td><td>Sigma Aldrich</td><td>S5761</td><td></td></tr><tr><td>NH4Cl</td><td>Sigma Aldrich</td><td>A9434</td><td></td></tr><tr><td>Nikon A1R confocal microscope</td><td>Nikon</td><td>A1R</td><td>inverted microscope, motorized x/y/z stage, NIS elements software</td></tr><tr><td>PBS</td><td>Life Technologies</td><td>D8537</td><td></td></tr><tr><td>phenol red free DMEM/F12</td><td>Life Technologies</td><td>21041-025</td><td>any phenol red free medium is suitable</td></tr><tr><td>PAM3CSK4</td><td>Invivogen</td><td>tlrl-pms</td><td>reconstitute in PBS</td></tr><tr><td>Rat serum</td><td>Stem Cell Technologies</td><td></td><td>included in EasySep Mouse Neutrophil Enrichement kit</td></tr><tr><td>Tissue culture dish 100</td><td>TPP</td><td>93100</td><td></td></tr></tbody></table>

imaging neutrophils and monocytes in mesenteric veins by intravital microscopy on anaesthetized mice in real time

Efficient immune response is dependent on rapid mobilization of blood leukocytes to the site of infection or injury. Investigating leukocyte migration in vivo is crucial for understanding the molecular basis of leukocyte transendothelial migration and interaction with vascular endothelium. One powerful approach involves intravital microscopy on transgenic mice expressing fluorescent proteins in cells of interest.
Here we present a protocol for imaging monocytes and neutrophils in the CX3CR1gfp/wt mouse i.v. injected with orange dye-labeled neutrophils with an inverted confocal microscope. Time-lapse movies gathered from 30 min&#160;to several hours of imaging allow the analysis of leukocyte behavior in mesenteric veins under both steady state and inflammatory conditions. We also describe the steps to locally induce blood vessel inflammation with TLR2/TLR1 agonist Pam3SK4 and monitor the subsequent recruitment of neutrophils and monocytes.
The presented technique can also be used to monitor other populations of leukocytes and investigate molecules implicated in leukocyte recruitment or trafficking using other stimuli or transgenic mice.

The manuscript describes an optimized protocol to easily monitor the behavior of monocytes and neutrophils in the mesenteric veins of anaesthetized mice in real time. The use of a 37 &#176;C-thermostated chamber is mandatory to maintain the temperature of the mouse and also due to the temperature dependent movement of leukocytes. Preparation of the mouse is displayed in Figure 1. Figure 2 shows all the area seen under the microscope. Transmitted light allows the identification of mesenteric veins (red ar...

Watch this Scientific Journal Video about Imaging Neutrophils and Monocytes in Mesenteric Veins by Intravital Microscopy on Anaesthetized Mice in Real Time at JoVE.com

Imaging Neutrophils and Monocytes in Mesenteric Veins by Intravital Microscopy on Anaesthetized Mice in Real Time

We detail a protocol to monitor the behavior of neutrophils and monocytes in mesenteric veins under steady state and inflammatory conditions using intravital confocal microscopy on anaesthetized mice.

Efficient immune response is dependent on rapid mobilization of blood leukocytes to the site of infection or injury. Investigating leukocyte migration in ...

imaging-neutrophils-monocytes-mesenteric-veins-intravital-microscopy

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Immunology and Infection

10.5K Views.  University of Geneva. We detail a protocol to monitor the behavior of neutrophils and monocytes in mesenteric veins under steady state and inflammatory conditions using intravital confocal microscopy on anaesthetized mice.

Video: Imaging Neutrophils and Monocytes in Mesenteric Veins by Intravital Microscopy on Anaesthetized Mice in Real Time

Tracking Neutrophil Intraluminal Crawling, Transendothelial Migration and Chemotaxis in Tissue by Intravital Video Microscopy

The recruitment of circulating leukocytes from blood stream to the inflamed tissue is a crucial and complex process of inflammation1,2. In the postcapillary venules of inflamed tissue, leukocytes initially tether and roll on the luminal surface of venular wall. Rolling leukocytes arrest on endothelium and undergo firm adhesion in response to chemokine or other chemoattractants on the venular surface. Many adherent leukocytes relocate from the initial site of adhesion to the junctional extravasation site in endothelium, a process termed intraluminal crawling3. Following crawling, leukocytes move across endothelium (transmigration) and migrate in extravascular tissue toward the source of chemoattractant (chemotaxis)4. Intravital microscopy is a powerful tool for visualizing leukocyte-endothelial cell interactions in vivo and revealing cellular and molecular mechanisms of leukocyte recruitment2,5. In this report, we provide a comprehensive description of using brightfield intravital microscopy to visualize and determine the detailed processes of neutrophil recruitment in mouse cremaster muscle in response to the gradient of a neutrophil chemoattractant. To induce neutrophil recruitment, a small piece of agarose gel (~1-mm3 size) containing neutrophil chemoattractant MIP-2 (CXCL2, a CXC chemokine) or WKYMVm (Trp-Lys-Tyr-Val-D-Met, a synthetic analog of bacterial peptide) is placed on the muscle tissue adjacent to the observed postcapillary venule. With time-lapsed video photography and computer software ImageJ, neutrophil intraluminal crawling on endothelium, neutrophil transendothelial migration and the migration and chemotaxis in tissue are visualized and tracked. This protocol allows reliable and quantitative analysis of many neutrophil recruitment parameters such as intraluminal crawling velocity, transmigration time, detachment time, migration velocity, chemotaxis velocity and chemotaxis index in tissue. We demonstrate that using this protocol, these neutrophil recruitment parameters can be stably determined and the single cell locomotion conveniently tracked in vivo.

We describe a protocol of brightfield intravital microscopy for measuring dynamic neutrophil-endothelial cell interactions during neutrophil recruitment in response to the source of a neutrophil chemoattractant in vivo. Neutrophil intraluminal crawling, transendothelial migration and chemotaxis in mouse cremaster muscle tissue are visualized with time-lapsed video photography and tracked with ImageJ.

The recruitment of circulating leukocytes from blood stream to the inflamed tissue is a crucial and complex process of inflammation1,2. In the ...

Real-time Imaging of Heterotypic Platelet-neutrophil Interactions on the Activated Endothelium During Vascular Inflammation and Thrombus Formation in Live Mice

Interaction of activated platelets and leukocytes (mainly neutrophils) on the activated endothelium mediates thrombosis and vascular inflammation.1,2 During thrombus formation at the site of arteriolar injury, platelets adherent to the activated endothelium and subendothelial matrix proteins support neutrophil rolling and adhesion.3 Conversely, under venular inflammatory conditions, neutrophils adherent to the activated endothelium can support adhesion and accumulation of circulating platelets. Heterotypic platelet-neutrophil aggregation requires sequential processes by the specific receptor-counter receptor interactions between cells.4 It is known that activated endothelial cells release adhesion molecules such as von Willebrand factor, thereby initiating platelet adhesion and accumulation under high shear conditions.5 Also, activated endothelial cells support neutrophil rolling and adhesion by expressing selectins and intercellular adhesion molecule-1 (ICAM-1), respectively, under low shear conditions.4 Platelet P-selectin interacts with neutrophils through P-selectin glycoprotein ligand-1 (PSGL-1), thereby inducing activation of neutrophil &beta;2 integrins and firm adhesion between two cell types. Despite the advances in in vitro experiments in which heterotypic platelet-neutrophil interactions are determined in whole blood or isolated cells,6,7 those studies cannot manipulate oxidant stress conditions during vascular disease. In this report, using fluorescently-labeled, specific antibodies against a mouse platelet and neutrophil marker, we describe a detailed intravital microscopic protocol to monitor heterotypic interactions of platelets and neutrophils on the activated endothelium during TNF-&alpha;-induced inflammation or following laser-induced injury in cremaster muscle microvessels of live mice.

Here we report an experimental technique of fluorescence intravital microscopy to visualize heterotypic platelet-neutrophil interactions on the activated endothelium during vascular inflammation and thrombus formation in live mice. This microscopic technology will be valuable to study the molecular mechanism of vascular disease and to test pharmacologic agents under pathophysiological conditions.

Interaction of activated platelets and leukocytes (mainly neutrophils) on the activated endothelium mediates thrombosis and vascular inflammation.1,2 ...

Intravital Microscopy of Leukocyte-endothelial and Platelet-leukocyte Interactions in Mesenterial Veins in Mice

Intravital microscopy is a method that can be used to investigate different processes in different regions and vessels in living animals. In this protocol, we describe intravital microscopy of mesentery veins. This can be performed in a short period of time with reproducible results showing leukocyte-endothelial interactions in vivo. We describe an inflammatory setting after LPS challenge of the endothelium. But in this model one can apply many different types of inflammatory conditions, like bacterial, chemical or biological and investigate the administration of drugs and their direct effects on the living animal and its impact on leukocyte recruitment. This protocol has been applied successfully to a number of different treatments of mice and their effects on inflammatory response in vessels. Herein, we describe the visualization of leukocytes and platelets by fluorescently labeling these with rhodamine 6G. Additionally, any specific imaging can be performed using targeted fluorescently labeled molecules.

This simplified application of intravital microscopy of mesentery veins in mice can be used in different models of inflammation to observe leukocyte-endothelial and platelet-leukocyte interactions.

Intravital microscopy is a method that can be used to investigate different processes in different regions and vessels in living animals. In this ...

Intravital Imaging of Neutrophil Priming Using IL-1&#946; Promoter-driven DsRed Reporter Mice

Neutrophils are the most abundant leukocytes in human blood circulation and are quickly recruited to inflammatory sites. Priming is a critical event that enhances the phagocytic functionality of neutrophils. Although extensive studies have unveiled the existence and importance of neutrophil priming during infection and injury, means of visualizing this process in vivo have been unavailable. The protocol provided enables monitoring of the dynamic process of neutrophil priming in living animals by combining three methodologies: 1) DsRed reporter signal &#8212; used as a measure of priming 2) in vivo neutrophil labeling &#8212; achieved by injection of fluorescence-conjugated anti-lymphocyte antigen 6G (Ly6G) monoclonal antibody (mAb) and 3) intravital confocal imaging. Several critical steps are involved in this protocol: oxazolone-induced mouse ear skin inflammation, appropriate sedation of animals, repeated injections of anti-Ly6G mAb, and prevention of focus drift during imaging. Although a few limitations have been observed, such as the limit of continuous imaging time (~ 8 hr) in one mouse and the leakage of fluorescein isothiocyanate-dextran from blood vessels in the inflammatory state, this protocol provides a fundamental framework for intravital imaging of primed neutrophil behavior and function, which can easily be expanded to examination of other immune cells in mouse inflammation models.

This current protocol employs fluorescent reporters, in vivo labeling, and intravital imaging techniques to enable monitoring of the dynamic process of neutrophil priming in living animals.

Neutrophils are the most abundant leukocytes in human blood circulation and are quickly recruited to inflammatory sites. Priming is a critical event that ...

Femur Window Chamber Model for In Vivo Cell Tracking in the Murine Bone Marrow

Bone marrow is a complex organ that contains various hematopoietic and non-hematopoietic cells. These cells are involved in many biological processes, including hematopoiesis, immune regulation and tumor regulation. Commonly used methods for understanding cellular actions in the bone marrow, such as histology and blood counts, provide static information rather than capturing the dynamic action of multiple cellular components in vivo. To complement the standard methods, a window chamber (WC)-based model was developed to enable serial in vivo imaging of cells and structures in the murine bone marrow. This protocol describes a surgical procedure for installing the WC in the femur, in order to facilitate long-term optical access to the femoral bone marrow. In particular, to demonstrate its experimental utility, this WC approach was used to image and track neutrophils within the vascular network of the femur, thereby providing a novel method to visualize and quantify immune cell trafficking and regulation in the bone marrow. This method can be applied to study various biological processes in the murine bone marrow, such as hematopoiesis, stem cell transplantation, and immune responses in pathological conditions, including cancer.

Femur Window Chamber Model for In Vivo Cell Tracking in the Murine Bone Marrow

The protocol describes a novel murine femur window chamber model that can be used to track movement of cells in the femoral bone marrow in vivo. Intravital multiphoton fluorescence microscopy is used to image three components of the femoral bone marrow (vasculature, collagen matrix, and neutrophils) over time.

Bone marrow is a complex organ that contains various hematopoietic and non-hematopoietic cells. These cells are involved in many biological processes, ...

Intravital Microscopy of Monocyte Homing and Tumor-Related Angiogenesis in a Murine Model of Peripheral Arterial Disease

The therapeutic goal for peripheral arterial disease and ischemic heart disease is to increase blood flow to ischemic areas caused by hemodynamic stenosis. Vascular surgery is a viable option in selected cases, but for patients without indications for surgery such as progression to rest pain, critical limb ischemia, or major disruptions to life or work, there are few possibilities for mitigating their disease. Cell therapy via monocyte-enhanced perfusion through the stimulation of collateral formation is one of a few non-invasive options.
Our group examines arteriogenesis after monocyte transplantation into mice using the hindlimb ischemia model. Previously, we have demonstrated improvement in hindlimb perfusion using tetanus-stimulated syngeneic monocyte transplantation. In addition to the effects on the collateral formation, tumor growth could be affected by this therapy as well. To investigate these effects, we use a basement membrane-like matrix mouse model by injecting the extracellular matrix of the Engelbreth-Holm-Swarm sarcoma into the flank of the mouse, after occlusion of the femoral artery.
After the artificial tumor studies, we use intravital microscopy to study in vivo tumor-angiogenesis and monocyte homing within collateral arteries. Previous studies have described the histological examination of animal models, which presupposes subsequent analysis to post-mortem artifacts. Our approach visualizes monocyte homing to areas of collateralization in real time sequences, is easy to perform, and investigates the process of arteriogenesis and tumor angiogenesis in vivo.

Monocytes are important mediators of arteriogenesis in the context of peripheral arterial disease. Using a basement membrane-like matrix and intravital microscopy, this protocol investigates monocyte homing and tumor-related angiogenesis after monocyte injection in the femoral artery ligation murine model.

The therapeutic goal for peripheral arterial disease and ischemic heart disease is to increase blood flow to ischemic areas caused by hemodynamic ...

Medicine

Intravital Imaging of Intraepithelial Lymphocytes in Murine Small Intestine

Intraepithelial lymphocytes expressing &#947;&#948; T cell receptor (&#947;&#948; IEL) play a key role in immune surveillance of the intestinal epithelium. Due in part to the lack of a definitive ligand for the &#947;&#948; T cell receptor, our understanding of the regulation of &#947;&#948; IEL activation and their function in vivo remains limited. This necessitates the development of alternative strategies to interrogate signaling pathways involved in regulating &#947;&#948; IEL function and the responsiveness of these cells to the local microenvironment. Although &#947;&#948; IELs are widely understood to limit pathogen translocation, the use of intravital imaging has been critical to understanding the spatiotemporal dynamics of IEL/epithelial interactions at steady-state and in response to invasive pathogens. Herein, we present a protocol for visualizing IEL migratory behavior in the small intestinal mucosa of a GFP &#947;&#948; T cell reporter mouse using inverted spinning disk confocal laser microscopy. Although the maximum imaging depth of this approach is limited relative to the use of two-photon laser-scanning microscopy, spinning disk confocal laser microscopy provides the advantage of high speed image acquisition with reduced photobleaching and photodamage. Using 4D image analysis software, T cell surveillance behavior and their interactions with neighboring cells can be analyzed following experimental manipulation to provide additional insight into IEL activation and function within the intestinal mucosa.

We describe a method to visualize GFP-labeled &#947;&#948; IELs using intravital imaging of murine small intestine by inverted spinning disk confocal microscopy. This technique enables the tracking of live cells within the mucosa for up to 4 h and can be used to investigate a variety of intestinal immune-epithelial interactions. &#160;

Intraepithelial lymphocytes expressing &#947;&#948; T cell receptor (&#947;&#948; IEL) play a key role in immune surveillance of the intestinal ...

Multiphoton Intravital Imaging for Monitoring Leukocyte Recruitment during Arteriogenesis in a Murine Hindlimb Model

Arteriogenesis strongly depends on leukocyte and platelet recruitment to the perivascular space of growing collateral vessels. The standard approach for analyzing collateral arteries and leukocytes in arteriogenesis is ex vivo (immuno-) histological methodology. However, this technique does not allow the measurement of dynamic processes such as blood flow, shear stress, cell-cell interactions, and particle velocity. This paper presents a protocol to monitor in vivo processes in growing collateral arteries during arteriogenesis utilizing intravital imaging. The method described here is a reliable tool for dynamics measurement and offers a high-contrast analysis with minimal photo-cytotoxicity, provided by multiphoton excitation microscopy. Prior to analyzing growing collateral arteries, arteriogenesis was induced in the adductor muscle of mice by unilateral ligation of the femoral artery.
After the ligation, the preexisting collateral arteries started to grow due to increased shear stress. Twenty-four hours after surgery, the skin and subcutaneous fat above the collateral arteries were removed, constructing a pocket for further analyses. To visualize blood flow and immune cells during in vivo imaging, CD41-fluorescein isothiocyanate (FITC) (platelets) and CD45-phycoerythrin (PE) (leukocytes) antibodies were injected intravenously (i.v.) via a catheter placed in the tail vein of a mouse. This article introduces intravital multiphoton imaging as an alternative or in vivo complementation to the commonly used static ex vivo (immuno-) histological analyses to study processes relevant for arteriogenesis. In summary, this paper describes a novel and dynamic in vivo method to investigate immune cell trafficking, blood flow, and shear stress in a hindlimb model of arteriogenesis, which enhances evaluation possibilities notably.

The recruitment of leukocytes and platelets constitutes an essential component necessary for the effective growth of collateral arteries during arteriogenesis. Multiphoton microscopy is an efficient tool for tracking cell dynamics with high spatio-temporal resolution in vivo and less photo-toxicity to study leukocyte recruitment and extravasation during arteriogenesis.

Arteriogenesis strongly depends on leukocyte and platelet recruitment to the perivascular space of growing collateral vessels. The standard approach for ...

Endothelial PAR1 Role in Leukocyte Adhesion and NET Formation During I/R Injury

Visualization of Neutrophil Extracellular Traps in Mesenteric Venules After Mesenteric Ischemia-Reperfusion Injury via Intravital Microscopy

Intestinal ischemia-reperfusion (I/R) injury is an acute condition characterized by tissue damage resulting from restricted blood flow to the mesenteric vessels, leading to both local and systemic pathologies with a poor prognosis. Both ischemia and reperfusion trigger a series of cellular and molecular responses, with inflammatory cells serving as key regulators of the pathology. These interactions with the ischemic endothelium are mediated by multiple adhesion receptors. Several animal models have been established to mimic this pathology and investigate the involved molecular pathways. In this study, a microsurgical model of I/R injury is combined with intravital microscopy to visualize leukocyte rolling, adhesion, and neutrophil extracellular trap (NET) formation. This model is applied to transgenic mice deficient in endothelial PAR1 (F2r) to assess the impact of PAR1 on leukocyte rolling and NET formation 1 h after ischemia and immediately following reperfusion. In vivo, Acridine Orange leukocyte staining was employed, and NETs were visualized using a nucleic acid stain. Interestingly, reduced leukocyte adhesion and NET formation were observed in mice lacking the endothelial PAR1 receptor. This model enables the in vivo analysis of key regulators involved in I/R injury.

This protocol presents a method for inducing mesenteric ischemia-reperfusion injury and visualizing neutrophil extracellular traps (NETs) in mesenteric venules using intravital microscopy. Blood flow in the superior mesenteric artery was restricted for 1 h, followed by reperfusion, allowing direct quantification of leukocyte adhesion and NETosis.

Intestinal ischemia-reperfusion (I/R) injury is an acute condition characterized by tissue damage resulting from restricted blood flow to the mesenteric ...

Imaging Neutrophil Migration in the Mouse Skin to Investigate Subcellular Membrane Remodeling Under Physiological Conditions

The study of immune cell recruitment and function in tissues has been a very active field over the last two decades. Neutrophils are among the first immune cells to reach the site of inflammation and to participate in the innate immune response during infection or tissue damage. So far, neutrophil migration has been successfully visualized using various in vitro experimental systems based on uniform stimulation, or confined migration under agarose, or micro-fluidic channels. However, these models do not recapitulate the complex microenvironment that neutrophils encounter in vivo. The development of multiphoton microscopy (MPM)-based techniques, such as intravital subcellular microscopy (ISMic), offer a unique tool to visualize and investigate neutrophil dynamics at subcellular resolutions under physiological conditions. In particular, the ear of a live anesthetized mouse provides an experimental advantage to follow neutrophil interstitial migration in real-time due to its ease of accessibility and lack of surgical exposure. ISMic provides the optical resolution, speed, and depth of acquisition necessary to track both cellular and, more importantly, subcellular processes in 3D over time (4D). Moreover, multi-modal imaging of the interstitial microenvironment (i.e., blood vessels, resident cells, extracellular matrix) can be readily accomplished using a combination of transgenic mice expressing select fluorescent markers, exogenous labeling via fluorescent probes, tissue intrinsic fluorescence, and second/third harmonic generated signals. This protocol describes 1) the preparation of neutrophils for adoptive transfer into the mouse ear, 2) different settings for optimal sub-cellular imaging, 3) strategies to minimize motion artifacts while maintaining a physiological response, 4) examples of membrane remodeling observed in neutrophils using ISMic, and 5) a workflow for the quantitative analysis of membrane remodeling in migrating neutrophils in vivo.

Neutrophil migration relies on the rapid and continuous remodeling of the plasma membrane in response to chemoattractant and its interactions with the extracellular microenvironment. Described herein is a procedure based on Intravital Subcellular Microscopy to investigate the dynamic of membrane remodeling in neutrophils injected in the ear of anesthetized mice.

The study of immune cell recruitment and function in tissues has been a very active field over the last two decades. Neutrophils are among the first ...

Imaging Neutrophils and Monocytes in Mesenteric Veins by Intravital Microscopy on Anaesthetized Mice in Real Time

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