This work was supported by the Deutsche Forschungsgemeinschaft (DU 1190/3-1).

All animal experiments were performed in compliance with the German animal protection law (TierSchG). The mice were housed and handled in accordance with good animal practice as defined by FELASA (www.felasa.eu/guidelines.php) and the national animal welfare body GV-SOLAS (www.gv-solas.de/index.html). The animal welfare committee of the University of Freiburg as well as the local authorities (Regierungspr&#228;sidium Freiburg) approved all animal experiments.
1. Animal Handling, Preparation and Induction of Inflammation
<ol>
	<li>Use 4 - 6 week old male mice with a weight range of 16 - 20 g. Note: If the mice are older or heavier they present excessive fat surrounding the vessel, limiting the microscopic observation.</li>
	<li>Sterilize all tools and microscope table prior to surgery.</li>
	<li>Inject 20 mg/kg LPS (lipopolysaccharide) intraperitoneally 4 hr&#160;prior to microscopy into the living mouse to induce a bacterial inflammation.</li>
	<li>Prewarm a 0.9% saline solution in a waterbath at 37 &#176;C to humidify the plastic chamber and the mesentery tissue.</li>
	<li>Anesthetize the mouse with intraperitoneal injection of ketamine (100 mg/kg) and xylazine (5 mg/kg) right before the microscopy procedure. Alternative anesthesia can be used, e.g., 2% isoflurane inhalation.&#160;Confirm proper anesthetization by the loss of response to reflex stimulation (toe or tail pinch with firm pressure).</li>
	<li>Depilate the abdomen using a shaver and remove loose hair with gauze saturated with ethanol 70%.</li>
	<li>Apply vet ointment on the eyes of the mouse to prevent dryness, while under anesthesia.</li>
</ol>
2. Surgery
<ol>
	<li>Sterilize the abdomen using 70% ethanol. This method is not a sterile method and could be lethal at the end of the experiment.</li>
	<li>Perform a median laparotomy: Open the abdominal skin using small, curved forceps and small scissors. Identify the epigastrical vessels and open the peritoneum in the region of the linea alba, to protect the vessels.</li>
	<li>Apply a few drops of prewarmed saline into the abdominal cavity to keep the tissue moist.</li>
	<li>Label leukocytes and platelets fluorescently by injecting 50 &#181;l rhodamine 6G (1 mg/ml) retro-orbitally as described before 9,10.</li>
	<li>Exteriorize a loop of ileumand place it in a petridish with a diameter of 10 cm and make sure to keep the tissue moist by applying the 37 &#176;C prewarmed saline solution (0.9%) every other minute.</li>
</ol>
3. Intravital Microscopy
<ol>
	<li>Place the Mouse underneath the microscope and bring the mesentery vein with a diameter of 200 - 300 &#181;m in the center of view. Choose a vessel with no visible fat surroundings.</li>
	<li>Do not touch the mesentery vessels thereby avoiding stimulation of the endothelium. Handle the ileum loop cautiously.</li>
	<li>Visualize blood cell-endothelial interactions with an inverted or upright microscope and a camera using a microscope software. Record blood cell-endothelial interactions for 1 min&#160;in 4 different veins per mouse.</li>
	<li>Euthanize the mouse by cervical dislocation after the completion of imaging experiments.</li>
</ol>
4. Analysis
<ol>
	<li>Carry out the analysis offline and blinded for all parameters. Carry out analysis using any suitable software program.</li>
	<li>Confirm stable and interindividually comparable blood flow conditions in high time-resolution cine-clips (maximal frame rate) focused on intraluminal blood cell flow.</li>
	<li>Quantify the number of rolling leukocytes. Therefor draw a vertical line through the vein and count all leukocytes crossing this line in 1 min.</li>
	<li>Determine rolling velocity by measuring the time one single leukocyte needs to pass a distance of 50 &#181;m while stably rolling on endothelium. To do this, draw two vertical lines in a distance of 50 &#181;m through the vein.
	<ol>
		<li>Measure the time a representative leukocyte needs to get from one line to the other.Calculate the speed of the leukocytes by dividing 50 &#181;m through the time needed (&#181;m/s).</li>
	</ol>
	</li>
	<li>Measure leukocyte adhesion in a field of 0.04 mm2 . To do this, draw a square with the side length of 200 &#181;m into the vein.
	<ol>
		<li>Count the firm adherent leukocytes, defined as no visible movement for 30 sec, within this square.</li>
	</ol>
	</li>
	<li>Count the number of platelets bound to one leukocyte to quantify platelet-leukocyte interactions.</li>
</ol>

<ol>
	<li>Lehr, H. A., Vollmar, B., Vajkoczy, P., Menger, 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=Intravital+fluorescence+microscopy+for+the+study+of+leukocyte+interaction+with+platelets+and+endothelial+cells.">Intravital fluorescence microscopy for the study of leukocyte interaction with platelets and endothelial cells.</a> Methods in enzymology. 300, 462-481 (1999).</li><li>Atherton, A., Born, G. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+investigations+of+the+adhesiveness+of+circulating+polymorphonuclear+leucocytes+to+blood+vessel+walls.">Quantitative investigations of the adhesiveness of circulating polymorphonuclear leucocytes to blood vessel walls.</a> The Journal of physiology. 222, 447-474 (1972).</li><li>Duerschmied, 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=Serotonin+stimulates+platelet+receptor+shedding+by+tumor+necrosis+factor-alpha-converting+enzyme+(ADAM17).">Serotonin stimulates platelet receptor shedding by tumor necrosis factor-alpha-converting enzyme (ADAM17).</a> Journal of thrombosis and haemostasis : JTH. 7, 1163-1171 (2009).</li><li>Chauhan, A. 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=ADAMTS13:+a+new+link+between+thrombosis+and+inflammation.">ADAMTS13: a new link between thrombosis and inflammation.</a> The Journal of experimental medicine. 205, 2065-2074 (1084).</li><li>Baez, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+open+cremaster+muscle+preparation+for+the+study+of+blood+vessels+by+in+vivo+microscopy.">An open cremaster muscle preparation for the study of blood vessels by in vivo microscopy.</a> Microvascular research. 5, 384-394 (1973).</li><li>Leister, I., 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=A+peritoneal+cavity+chamber+for+intravital+microscopy+of+the+liver+under+conditions+of+pneumoperitoneum.">A peritoneal cavity chamber for intravital microscopy of the liver under conditions of pneumoperitoneum.</a> Surgical endoscopy. 17, 939-942 (2003).</li><li>Duerschmied, 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=Platelet+serotonin+promotes+the+recruitment+of+neutrophils+to+sites+of+acute+inflammation+in+mice.">Platelet serotonin promotes the recruitment of neutrophils to sites of acute inflammation in mice.</a> Blood. 121, 1008-1015 (2013).</li><li>Herr, N., 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=Acute+fluoxetine+treatment+induces+slow+rolling+of+leukocytes+on+endothelium+in+mice.">Acute fluoxetine treatment induces slow rolling of leukocytes on endothelium in mice.</a> PloS one. 9, e88316 (2014).</li><li>Yardeni, T., Eckhaus, M., Morris, H. 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The authors have nothing to disclose.

Herein we describe the preparation and performance of intravital microscopy of mesentery veins of mice in vivo. This method gives us the opportunity to observe leukocyte-endothelial and platelet-endothelial interactions11 directly in the living organism.
As an early response to inflammation the endothelium gets activated and interacts with leukocytes and platelets resulting in rolling, adhesion and transmigration12. But leukocytes also interact with platelets for...

The purpose of this protocol is to describe a simplified technique of intravital microscopy of mesentery veins in living mice for direct observation of leukocyte-endothelial and leukocyte-platelet interactions under inflammatory conditions.
Intravital microscopy was developed to study leukocyte-endothelial interactions in vivo under inflammatory conditions1,2, which is not trivial but important for understanding inflammatory leukocyte recruitment and function. The method we describe in this protocol was developed based on previously published publications. Similar to visualizing platelet incorporation in a growing thrombus3 and in parallel to what has been published earlier4, an exteriorized mesentery vein is examined by transmitted light microscopy. There are various other models of intra-vital microscopy such as the cremaster muscle of rats5 or liver of mouse and rats6.
Intravital microscopy of mesentery vein has been developed and applied in previous studies by several groups. We have used this technique to observe differences in leukocyte recruitment between wild type mice and tryptophane hydroxylase1 (Tph1) -/- mice, which are deficient of non-neuronal serotonin and compared the findings to mice whose platelet serotonin was pharmacologically depleted by long-term application the a selective serotonin reuptake inhibitor fluoxetine7. We have also examined leukocyte-endothelial interactions after acute fluoxetine treatment8.
In this protocol we focus on intravital microscopy of mesentery veins, because this model can be performed quickly, and allows valid measurements of leukocyte-endothelial and platelet-leukocyte interactions. This is much more challenging and time-consuming in intravital microscopy of other organs, such as bone, liver, skin, or cremaster muscle. The model described here is ideal for reproducible evaluation of inflammatory cell-cell interaction after challengeing it with an inflammatory stimulus, such as intraperitoneal injection of lipopolysaccharide.

<table><tbody><tr><td>Rhodamine 6G</td><td>Sigma-Aldrich</td><td>&amp;nbsp;989-38-8</td><td></td></tr><tr><td>Lipopolysaccharides from Escherichia coli 055:B5</td><td>Sigma-Aldrich</td><td>L2637&amp;nbsp;</td><td></td></tr></tbody></table>

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.

An overview of the experimental setting described in this protocol is shown in Figure 1. It shows a mouse with an exteriorized ileum-loop and its vessels, which can be observed in intravital microscopy. Figure 2 shows certain degree of activation in untreated animals due to the procedure itself. But there is almost no slow rolling or firm adhesion of leukocytes compared to LPS-treated mice. Figure 2 also shows the different results of intravital microscopy in wildtype mi...

Watch this Scientific Journal Video about Intravital Microscopy of Leukocyte-endothelial and Platelet-leukocyte Interactions in Mesenterial Veins in Mice at JoVE.com

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

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-microscopy-leukocyte-endothelial-platelet-leukocyte

Research

JoVE Journal

Immunology and Infection

12.1K Views.  Heart Center, University of Freiburg. 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.

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

Intravital Microscopy of the Mouse Brain Microcirculation using a Closed Cranial Window

This experimental model was designed to assess the mouse pial microcirculation during acute and chronic, physiological and pathophysiological hemodynamic, inflammatory and metabolic conditions, using in vivo fluorescence microscopy. A closed cranial window is placed over the left parieto-occipital cortex of the mice. Local microcirculation is recorded in real time through the window using epi and fluorescence illumination, and measurements of vessels diameters and red blood cell (RBC) velocities are performed. RBC velocity is measured using real-time cross-correlation and/or fluorescent-labeled erythrocytes. Leukocyte and platelet adherence to pial vessels and assessment of perfusion and vascular leakage are made with the help of fluorescence-labeled markers such as Albumin-FITC and anti-CD45-TxR antibodies. Microcirculation can be repeatedly video-recorded over several days. We used for the first time the close window brain intravital microscopy to study the pial microcirculation to follow dynamic changes during the course of Plasmodium berghei ANKA infection in mice and show that expression of CM is associated with microcirculatory dysfunctions characterized by vasoconstriction, profound decrease in blood flow and eventually vascular collapse.

Intravital microscopy to follow temporal and spatial hemodynamic and inflammatory events in the pial microcirculation.

This experimental model was designed to assess the mouse pial microcirculation during acute and chronic, physiological and pathophysiological hemodynamic, ...

Neuroscience

Intravital Microscopy of the Inguinal Lymph Node

Lymph nodes (LN's), located throughout the body, are an integral component of the immune system. They serve as a site for induction of adaptive immune response and therefore, the development of effector cells. As such, LNs are key to fighting invading pathogens and maintaining health. The choice of LN to study is dictated by accessibility and the desired model; the inguinal lymph node is well situated and easily supports studies of biologically relevant models of skin and genital mucosal infection.
The inguinal LN, like all LNs, has an extensive microvascular network supplying it with blood. In general, this microvascular network includes the main feed arteriole of the LN that subsequently branches and feeds high endothelial venules (HEVs). HEVs are specialized for facilitating the trafficking of immune cells into the LN during both homeostasis and infection. How HEVs regulate trafficking into the LN under both of these circumstances is an area of intense exploration. The LN feed arteriole, has direct upstream influence on the HEVs and is the main supply of nutrients and cell rich blood into the LN. Furthermore, changes in the feed arteriole are implicated in facilitating induction of adaptive immune response. The LN microvasculature has obvious importance in maintaining an optimal blood supply to the LN and regulating immune cell influx into the LN, which are crucial elements in proper LN function and subsequently immune response. 
The ability to study the LN microvasculature in vivo is key to elucidating how the immune system and the microvasculature interact and influence one another within the LN. Here, we present a method for in vivo imaging of the inguinal lymph node. We focus on imaging of the microvasculature of the LN, paying particular attention to methods that ensure the study of healthy vessels, the ability to maintain imaging of viable vessels over a number of hours, and quantification of vessel magnitude. Methods for perfusion of the microvasculature with vasoactive drugs as well as the potential to trace and quantify cellular traffic are also presented. 
Intravital microscopy of the inguinal LN allows direct evaluation of microvascular functionality and real-time interface of the direct interface between immune cells, the LN, and the microcirculation. This technique potential to be combined with many immunological techniques and fluorescent cell labelling as well as manipulated to study vasculature of other LNs.

A technique for performing intravital microscopy of the inguinal lymph node (LN) is outlined. Such technique allows for real-time, in vivo study of the lymph node microvasculature and structure both during homeostasis and infection. This technique can be adapted to cell trafficking studies and to other lymph node sites.

Lymph nodes (LN's), located throughout the body, are an integral component of the immune system. They serve as a site for induction of adaptive immune ...

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 ...

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.

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 ...

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

Leukocyte Infiltration of Cremaster Muscle in Mice Assessed by Intravital Microscopy

Intravital microscopy (IVM) is widely used to monitor physiological and pathophysiological processes within the leukocyte recruitment cascade in vivo. The current protocol represents a practical and reproducible method to visualize the leukocyte endothelium interaction leading to leukocyte recruitment in skeletal muscle derived tissue within the intact organism of the mouse. The model is applicable to all fields of research that focus on granulocyte activation and their role in disease.
We provide a step by step protocol to guide through the method and to highlight potential pitfalls and technical difficulties. The protocol covers the following aspects: experimental settings and required material, anesthesia of the mouse, dissection of the cremaster muscle as well as tracheal and carotid cannulation, IVM recordings and offline analysis. Data formats like adherent leukocytes, rolling flux (RF) and rolling flux fraction (RFF) are explained in detail and appropriate applications are discussed. Representative results from dystrophin deficient mdx mice are provided in the results section.
IVM is a powerful tool to assess leukocyte recruitment in an in vivo setting; however, delineating for example endothelial and leukocyte function may require a combination with ex vivo setups like flow chamber experiments. Furthermore, the genetic background of animals of interest may greatly influence baseline recruitment, requiring individual fine tuning of the protocol provided. Despite its limitations, IVM may serve as a platform to readily translate in vitro findings into a living vertebrate organism.

Here, we show how to perform intravital microscopy on post-capillary venules of the mouse cremaster muscle. Commonly applied to different models of inflammation and sepsis, particularly those induced by chemokines and cytokines, we highlight its relevance in the study of muscolopathies involving exaggerated muscular leukocyte infiltration.

Intravital microscopy (IVM) is widely used to monitor physiological and pathophysiological processes within the leukocyte recruitment cascade in vivo. The ...

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 ...

Intravital Microscopy to Study Platelet-Leukocyte-Endothelial Interactions in the Mouse Liver

Inflammation and thrombosis are complex processes that occur primarily in the microcirculation. Although standard histology may provide insight into the end pathway for both inflammation and thrombosis, it is not capable of showing the temporal changes that occur throughout the time course of these processes. Intravital microscopy (IVM) is the use of live-animal imaging to gain temporal insight into physiologic processes in vivo. This method is particularly powerful when assessing cellular and protein interactions within the circulation due to the rapid and sequential events that are often necessary for these interactions to occur. While IVM is an extremely powerful imaging methodology capable of viewing complex processes in vivo, there are a number of methodological factors that are important to consider when planning an IVM study. This paper outlines the process of conducting intravital imaging of the liver, identifying important considerations and potential pitfalls that may arise. Thus, this paper describes the use of IVM to study platelet-leukocyte-endothelial interactions in liver sinusoids to study the relative contributions of each in different models of acute liver injury.

Intravital microscopy is a powerful tool that provides insight into both the temporal and spatial relationships of rapid and/or sequential processes. Herein, we describe a protocol to assess both protein-protein interactions and platelet-neutrophil-endothelial interactions in liver sinusoids in a murine model of experimental sepsis (endotoxemia).

Inflammation and thrombosis are complex processes that occur primarily in the microcirculation. Although standard histology may provide insight into the ...

Biology

Intravital Microscopy to Analyze Blood Cell-Endothelial Interactions in an Inflammation Mouse Model

Source: Herr, N. et al., <a href="https://app.jove.com/v/53077">Intravital Microscopy of Leukocyte-endothelial and Platelet-leukocyte Interactions in Mesenterial Veins in Mice.</a> J. Vis. Exp. (2015)
In this video, we demonstrate the real-time visualization of blood cell-endothelial interactions in the mesenterial veins of a mouse model injected intraperitoneally with lipopolysaccharide.

Source: Herr, N. et al., Intravital Microscopy of Leukocyte-endothelial and Platelet-leukocyte Interactions in Mesenterial Veins in Mice. J. Vis. Exp. ...