This study was supported by a grant from the National Research Foundation of Korea (NRF) funded by the Korea government (MSIP; grant no. 2016R1A2B4008199 to Y-M. H.), and the Ministry of Health &amp; Welfare, Republic of Korea (grant number: HI14C1324).

All procedures were conducted in accordance with the guidelines of the Institutional Animal Care and Use Committee of Yonsei University College of Medicine, Korea. LysM-green fluorescent protein (GFP; gfp/+) mice8 and CX3Cr1-GFP (gfp/+)9 mice at 8-12 weeks of age were used for intravital imaging.&#160;All surgical tools were autoclaved and disinfected with 70 % alcohol.
1. Custom-designed mouse liver imaging chamber with supporting tools
<ol>
	<li>Mouse liver imaging chamber design
	<ol>
		<li>Make a chamber of the following size for mouse liver imaging (Figure 1): inner chamber (120 mm length &#215; 160 mm width &#215; 30 mm height), outer chamber (100 mm length &#215; 100 mm width &#215; 24 mm height), bolts (&#1060; 3 mm &#215; 30 mm height), nuts (&#1060; 4 mm), and wing-shaped nuts (&#1060; 4 mm).</li>
		<li>Measure the curing agent and elastomer base in 1:9 ratio to make a total of 120 g of silicone.</li>
		<li>Put the liquid silicone mixture in a 250 mL Erlenmeyer flask and mix it well. Then put the flask in a desiccator and remove air bubbles for about 1 h under vacuum through the pump.</li>
		<li>Pour the liquid silicone mix into a custom-designed mouse chamber as high as 10 mm height and let it cure for a couple of days (Figure 1A).</li>
	</ol>
	</li>
	<li>Preparation of cover slides and the liver fixing bed
	<ol>
		<li>On the metal frame, attach the cover glass using silicone glue. Let it dry for 1 day (Figure 1B).</li>
		<li>In order to effectively hold the distilled water for the water immersion lens, a semipermanent water-blocking structure is essential. Make 1 mm rounding silicone glue and harden it overnight.</li>
		<li>Mix the curing agent and elastomer base and then pour it into a 6-well plate at a height of about 8-10 mm. Perform the hardening process as described in 1.1.2-1.1.4.</li>
	</ol>
	</li>
</ol>
2. Preparation of LPS
<ol>
	<li>Prepare sterile 1&#215; phosphate-buffered saline (PBS) to dilute the LPS powder from Salmonella enterica serotype enteritidis. (1&#215; PBS: 137 mM NaCl, 2.7 mM KCl, 10 mM Na2HPO4, 1.8 mM KH2PO4).</li>
	<li>Pre-heat PBS in water bath at 37 &#176;C, and open the LPS powder bottle (25 mg) carefully.</li>
	<li>Using a pipet aid, pour the sterile PBS (5 mL) into the LPS powder bottle and gently stir or suspend the solution to prepare the stock solution. 
	NOTE: After LPS powder is liquefied, harsh vortexing can cause bubbles. Avoid making bubbles to minimize loss when making aliquots in 1.5-mL tubes.</li>
	<li>Store the stock LPS solution at &#8722;20 &#176;C, and dilute it into a 1 mg/mL LPS solution for injection.</li>
	<li>Inject the 1 mg/mL LPS solution (20 mg/kg) into the peritoneum of a non-anesthetized mouse using a 1-mL syringe. For the control animal, inject the same volume of PBS.</li>
	<li>Wait for 2 h for sufficient inflammatory response.</li>
</ol>
3. Preparation of Texas-Red Dextran to stain blood vessels
<ol>
	<li>Prepare two 15-mL conical tubes and 10 mL of sterile PBS.</li>
	<li>Dilute Texas-Red Dextran powder (25 mg) in 3 mL of PBS and mix it well. Transfer the mixture to an empty 15-mL conical tube.</li>
	<li>Transfer the remaining PBS (7 mL) to the 15-mL conical tube containing the dextran mixture (3 mL).</li>
	<li>Connect a 0.45 &#181;m syringe filter to the tip of a 10-mL syringe. The syringe filter should replace the needle.</li>
	<li>Filter the dextran mixture (10 mL). Press the syringe evenly in order to avoid spilling.</li>
	<li>Dispense 500 &#181;L of 2.5 mg/mL dextran solution in the light-blocked 1.5-mL tube and store it at &#8722;20 &#176;C. Once thawed, store it at 4&#176;C.</li>
</ol>
4. Surgical process
<ol>
	<li>Disinfect the surgery table and all instruments using 70% alcohol prior to the surgery. Then, set the tools for the liver surgery and adjust the heating plate to 37 &#176;C (Figure 2A, B).</li>
	<li>For anesthesia, intraperitoneally inject the mice with 30 mg/kg of tiletamine/zolazepam&#160; and 10 mg/kg of xylazine. These solutions can be mixed and diluted in PBS for simultaneous injection. Confirm anesthetization by gently pressing the toe of the mouse.&#160;&#160;Proceed next step when there is no reflex.</li>
	<li>Apply small amount of eye ointment to prevent the dryness of mouse&#39;s retina.</li>
	<li>Remove body hair around the abdomen area using&#160;hair removal cream (Figure 2C).</li>
	<li>Inject 200 &#181;L of Texas-Red Dextran solution (concentration of 2.5 mg/mL) via the tail vein or retro-orbital injection using an insulin syringe (Figure 2D).</li>
	<li>Mark the right subcostal area with a marker. The line should be drawn from the xiphoid process to the end of the rib. Cut the epidermis with forceps and scissors (Figure 2E, F).</li>
	<li>Open the abdominal cavity using micro-scissors and forceps, and expose the liver carefully. The left lateral lobe should be rolled out using cotton swabs (Figure 2G, H).</li>
	<li>Pour 500 &#181;L of sterile PBS on the abdominal cavity to prevent dryness of the liver.</li>
	<li>Place the mouse in the right-decubitus position in a custom-designed chamber, and apply a small amount of tissue glue to the silicon bed. Then, carefully attach the liver using cotton swabs (Figure 2I). 
	NOTE: Because the liver tissue is extremely friable, do not mechanically pull out the liver. Gently roll it out with cotton swabs.</li>
	<li>A few seconds later, wet the liver again with 500 &#181;L of sterile PBS to avoid drying out of the liver. Place the metal frame on the liver and fix it firmly with nuts (Figure 2J).</li>
</ol>
5. Intravital imaging of the liver with two-photon microscopy
<ol>
	<li>Run ZEN software (Carl Zeiss) to turn on the laser, set the wavelength to 880 nm, and set green, and red channels. Adjust laser power according to fluorescence intensity (Figure 3A). Emission filter information is as follows: Green/Alexa488, 500-550 nm and Red/Alexa 555, 575-610 nm.</li>
	<li>Place the chamber on the imaging stage and place the 20X water-immersion objective lens close to the cover glass.</li>
	<li>Fix the silicone rubber heater under the mouse body to maintain its body temperature (Figure 3B).</li>
	<li>Drop 500 &#181;L of distilled water on the metal frame, and then pull the objective lens close to the liver (Figure 3C).</li>
	<li>Adjust the focus and determine the depth and time of the imaging area.</li>
	<li>Conduct imaging.</li>
	<li>For long-term imaging, inject half a dose of tiletamine/zolazepam and xylazine mixture&#160; each hour during imaging.&#160;Maintaining the body temperature of the mice at 37 &#176;C is essential during this stage. Always keep on eye to the mouse, since anesthetization time differs from every mouse. 
	NOTE: This method is not suitable for recovery after surgery and imaging. We ethically sacrifice the mouse immediately after surgery.</li>
	<li>Check the pedal reflexes for every 30 min for stable anesthetization.</li>
</ol>
6. Data analysis
<ol>
	<li>Open the data analysis software Volocity and then import the raw data in the library into the software.</li>
	<li>Remove noise from the image to suit the situation and take a snapshot. 
	NOTE: To obtain smooth images, use the &#39;Fine&#39; or &#39;Median&#39; filter. Furthermore, use the &#39;Contrast enhancement&#39; feature to make dark or blurry images clearer.</li>
	<li>Fit the edited items to 100% and export as JPEG or TIFF files for snapshot images and AVI files for movies.</li>
</ol>

<ol>
	<li>Girard, J. 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=Fuels,+hormones,+and+liver+metabolism+at+term+and+during+the+early+postnatal+period+in+the+rat.">Fuels, hormones, and liver metabolism at term and during the early postnatal period in the rat.</a> J Clin Invest. 52 (12), 3190-3200 (1973).</li><li>Marques, P. E., 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=Imaging+liver+biology+in+vivo+using+conventional+confocal+microscopy.">Imaging liver biology in vivo using conventional confocal microscopy.</a> Nat Protoc. 10 (2), 258-268 (2015).</li><li>Dasari, S., Weber, P., Makhloufi, C., Lopez, E., Forestier, C. L. <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+Imaging+of+the+Liver+following+Leishmania+Infection:+An+Assessment+of+Hepatic+Hemodynamics.">Intravital Microscopy Imaging of the Liver following Leishmania Infection: An Assessment of Hepatic Hemodynamics.</a> J Vis Exp. (101), e52303 (2015).</li><li>Honda, 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=Intravital+imaging+of+neutrophil+recruitment+in+hepatic+ischemia-reperfusion+injury+in+mice.">Intravital imaging of neutrophil recruitment in hepatic ischemia-reperfusion injury in mice.</a> Transplantation. 95 (4), 551-558 (2013).</li><li>Jenne, C. N., Wong, C. H., Petri, B., Kubes, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+spinning-disk+confocal+microscopy+for+the+intravital+analysis+of+platelet+dynamics+in+response+to+systemic+and+local+inflammation.">The use of spinning-disk confocal microscopy for the intravital analysis of platelet dynamics in response to systemic and local inflammation.</a> PLoS One. 6 (9), e25109 (2011).</li><li>Ritsma, 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=Intravital+microscopy+through+an+abdominal+imaging+window+reveals+a+pre-micrometastasis+stage+during+liver+metastasis.">Intravital microscopy through an abdominal imaging window reveals a pre-micrometastasis stage during liver metastasis.</a> Sci Transl Med. 4 (158), 158ra145 (2012).</li><li>Sierro, 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=A+Liver+Capsular+Network+of+Monocyte-Derived+Macrophages+Restricts+Hepatic+Dissemination+of+Intraperitoneal+Bacteria+by+Neutrophil+Recruitment.">A Liver Capsular Network of Monocyte-Derived Macrophages Restricts Hepatic Dissemination of Intraperitoneal Bacteria by Neutrophil Recruitment.</a> Immunity. 47 (2), 374-388 (2017).</li><li>Faust, N., Varas, F., Kelly, L. M., Heck, S., Graf, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insertion+of+enhanced+green+fluorescent+protein+into+the+lysozyme+gene+creates+mice+with+green+fluorescent+granulocytes+and+macrophages.">Insertion of enhanced green fluorescent protein into the lysozyme gene creates mice with green fluorescent granulocytes and macrophages.</a> Blood. 96 (2), 719-726 (2000).</li><li>Jung, 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=Analysis+of+fractalkine+receptor+CX(3)CR1+function+by+targeted+deletion+and+green+fluorescent+protein+reporter+gene+insertion.">Analysis of fractalkine receptor CX(3)CR1 function by targeted deletion and green fluorescent protein reporter gene insertion.</a> Mol Cell Biol. 20 (11), 4106-4114 (2000).</li><li>Heymann, 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=Long+term+intravital+multiphoton+microscopy+imaging+of+immune+cells+in+healthy+and+diseased+liver+using+CXCR6.Gfp+reporter+mice.">Long term intravital multiphoton microscopy imaging of immune cells in healthy and diseased liver using CXCR6.Gfp reporter mice.</a> J Vis Exp. (97), (2015).</li></ol>

The authors declare no competing financial interests.

The liver has been actively studied by many groups3,10, due to importance of its function. For instance, Heymann et al. suggested a delicate method using agarose. Although this method was found to be highly precise, the agarose setting takes time. However, with our methodology, all procedures could be carried out within 30 min, minimizing other confounding factors. Second, stabilizing the liver is extremely important because the heartbeat can disturb the video. T...

The liver is the major metabolic organ in mammals; it acts as a control tower for energy, hormones, and detoxification1. Due to its importance, researchers have conducted many in vitro and in vivo experiments to elucidate the changes in the liver during inflammation. Intravital microscopy has been used to capture live images from the liver2 . Indeed, various liver imaging methods have been introduced2,3,4,5,6. However, in order to develop a more simplified surgical approach and achieve stabilization of the target organ and the immune cells, we designed a simple protocol that can guide researchers to minimize their effort for intravital imaging.
In this study, we introduced a stable and novel imaging chamber and surgical technique that could be used to minimize bleeding and possible infections. We confirmed that the liver remained intact for more than 2 h. With this method, we successfully identified morphologies of LCMs7 and neutrophils under septic condition. Since this method minimizes physical and biological confounding factors such as trembling and unexpected inflammation during surgical procedure, we anticipate that this method could be used to observe acute reactions of immune cells in the liver in response to reagents like LPS.

<table border="0" cellpadding="0" cellspacing="0" width="1004">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Custom designed chamber</td>
			<td style="width:239px;">Live Cell Instruments</td>
			<td style="width:272px;"></td>
			<td style="width:233px;">Custom-designed size</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Metal cover slide</td>
			<td style="width:239px;">Live Cell Instruments</td>
			<td style="width:272px;"></td>
			<td style="width:233px;">Custom-designed size</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Cover glass</td>
			<td style="width:239px;">Electron Microscopy Sciences</td>
			<td style="width:272px;">#72204-03</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Sylgard 184 Silicone elastomer kit</td>
			<td style="width:239px;">Dow Corning</td>
			<td style="width:272px;"></td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Erlenmeyer flask</td>
			<td style="width:239px;">DURAN</td>
			<td style="width:272px;">21 216 36</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Cell culture plate (Flat type)</td>
			<td style="width:239px;">HYUNDAI Micro Co.</td>
			<td style="width:272px;">H31006</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Desiccator</td>
			<td style="width:239px;">ADARSH</td>
			<td style="width:272px;">55204</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">High Q BOND SE 5 mL</td>
			<td style="width:239px;">BJM LAB</td>
			<td style="width:272px;"></td>
			<td style="width:233px;">To make semi-permanent dam</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Flexible Silicone Rubber Heaters</td>
			<td style="width:239px;">Omega</td>
			<td style="width:272px;">SRFR/SRFG SERIES, M1250/0800</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">DC power supply</td>
			<td style="width:239px;">Toyotech</td>
			<td style="width:272px;">DP30-03A</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Phosphate-buffered saline</td>
			<td style="width:239px;"></td>
			<td style="width:272px;"></td>
			<td style="width:233px;">Home-made</td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:260px;">Lipopolysaccharides (LPS) from Salmonella enteria serotype enteritidis</td>
			<td style="width:239px;">Sigma-Aldrich</td>
			<td style="width:272px;">L6011</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Texas Red Dextran</td>
			<td style="width:239px;">Thermo Fisher Scientific</td>
			<td style="width:272px;">D1830</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:260px;">15 mL High-clarity polypropylene 
			conical tube</td>
			<td style="width:239px;">FALCON</td>
			<td style="width:272px;">14-959-49B</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:260px;">0.45 &#956;m filter (Minisart Syringe Filter)</td>
			<td style="width:239px;">Sartorius</td>
			<td style="width:272px;">16555k</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">1.5ml Micro Tube, Amber</td>
			<td style="width:239px;">Axygen</td>
			<td style="width:272px;">MCT-150-X</td>
			<td style="width:233px;">For light-blocking</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">1 mL syringe</td>
			<td style="width:239px;">Korea Vaccine</td>
			<td style="width:272px;">KV-S01</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">3 mL syringe</td>
			<td style="width:239px;">Korea Vaccine</td>
			<td style="width:272px;">KV-S03</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">10 mL syringe</td>
			<td style="width:239px;">Korea Vaccine</td>
			<td style="width:272px;">KV-S10</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">0.3 mL insulin syringe</td>
			<td style="width:239px;">Becton Dickinson</td>
			<td style="width:272px;">324900</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Hair removal cream 100 mL</td>
			<td style="width:239px;">Body natur</td>
			<td style="width:272px;"></td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Cotton swab</td>
			<td style="width:239px;">ABDI</td>
			<td style="width:272px;"></td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Zoletil 50 5 mL</td>
			<td style="width:239px;">Virbac</td>
			<td style="width:272px;"></td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Rompun 10 mL</td>
			<td style="width:239px;">Bayer</td>
			<td style="width:272px;"></td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Heating plate</td>
			<td style="width:239px;">Live Cell Instruments</td>
			<td style="width:272px;">PH-S-10</td>
			<td style="width:233px;">Custom-designed size</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">DC controller</td>
			<td style="width:239px;">Live Cell Instruments</td>
			<td style="width:272px;">CU-301</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Microdessection Scissors</td>
			<td style="width:239px;">Harvard Apparatus</td>
			<td style="width:272px;">72-5418</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Scissors</td>
			<td style="width:239px;">Roboz</td>
			<td style="width:272px;">RS-5882</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Forceps</td>
			<td style="width:239px;">Roboz</td>
			<td style="width:272px;">RS-5137</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Vet bond</td>
			<td style="width:239px;">3M</td>
			<td style="width:272px;">1469SB</td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">ZEN software (Black Edition)</td>
			<td style="width:239px;">Carl Zeiss</td>
			<td style="width:272px;"></td>
			<td style="width:233px;">Program for LSM 7 MP</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">LSM 7 MP</td>
			<td style="width:239px;">Carl Zeiss</td>
			<td style="width:272px;"></td>
			<td style="width:233px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Volocity</td>
			<td style="width:239px;">PerkinElmer</td>
			<td style="width:272px;"></td>
			<td style="width:233px;">Analysis program</td>
		</tr>
	</tbody>
</table>

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.

A simple and very stable imaging chamber was devised. The bottom of chamber was covered with silicone, which prevented slipping of the mouse body and organs. Additionally, because silicon has the proper amount of elasticity, it could prevent expected damage induced by the pressure of the cover slide (Figure 1A, C). Second, tissue-safe glue (Vet bond) was applied in order to fix the extracted liver on the circle-shaped silicone bed. This metho...

Watch this Scientific Journal Video about Two-photon Intravital Imaging of Leukocytes During the Immune Response in Lipopolysaccharide-treated Mouse Liver at JoVE.com

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

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 ...

two-photon-intravital-imaging-leukocytes-during-immune-response

Research

JoVE Journal

Immunology and Infection

10.1K Views.  Yonsei University College of Medicine. 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. 

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

An Introduction to Parasitic Wasps of Drosophila and the Antiparasite Immune Response

Most known parasitoid wasp species attack the larval or pupal stages of Drosophila. While Trichopria drosophilae infect the pupal stages of the host (Fig. 1A-C), females of the genus Leptopilina (Fig. 1D, 1F, 1G) and Ganaspis (Fig. 1E) attack the larval stages. We use these parasites to study the molecular basis of a biological arms race. Parasitic wasps have tremendous value as biocontrol agents. Most of them carry virulence and other factors that modify host physiology and immunity. Analysis of Drosophila wasps is providing insights into how species-specific interactions shape the genetic structures of natural communities. These studies also serve as a model for understanding the hosts' immune physiology and how coordinated immune reactions are thwarted by this class of parasites.
The larval/pupal cuticle serves as the first line of defense. The wasp ovipositor is a sharp needle-like structure that efficiently delivers eggs into the host hemocoel. Oviposition is followed by a wound healing reaction at the cuticle (Fig. 1C, arrowheads). Some wasps can insert two or more eggs into the same host, although the development of only one egg succeeds. Supernumerary eggs or developing larvae are eliminated by a process that is not yet understood. These wasps are therefore referred to as solitary parasitoids.
Depending on the fly strain and the wasp species, the wasp egg has one of two fates. It is either encapsulated, so that its development is blocked (host emerges; Fig. 2 left); or the wasp egg hatches, develops, molts, and grows into an adult (wasp emerges; Fig. 2 right). L. heterotoma is one of the best-studied species of Drosophila parasitic wasps. It is a "generalist," which means that it can utilize most Drosophila species as hosts1. L. heterotoma and L. victoriae are sister species and they produce virus-like particles that actively interfere with the encapsulation response2. Unlike L. heterotoma, L. boulardi is a specialist parasite and the range of Drosophila species it utilizes is relatively limited1. Strains of L. boulardi also produce virus-like particles3 although they differ significantly in their ability to succeed on D. melanogaster1. Some of these L. boulardi strains are difficult to grow on D. melanogaster1 as the fly host frequently succeeds in encapsulating their eggs. Thus, it is important to have the knowledge of both partners in specific experimental protocols.
In addition to barrier tissues (cuticle, gut and trachea), Drosophila larvae have systemic cellular and humoral immune responses that arise from functions of blood cells and the fat body, respectively. Oviposition by L. boulardi activates both immune arms1,4. Blood cells are found in circulation, in sessile populations under the segmented cuticle, and in the lymph gland. The lymph gland is a small hematopoietic organ on the dorsal side of the larva. Clusters of hematopoietic cells, called lobes, are arranged segmentally in pairs along the dorsal vessel that runs along the anterior-posterior axis of the animal (Fig. 3A). The fat body is a large multifunctional organ (Fig. 3B). It secretes antimicrobial peptides in response to microbial and metazoan infections.
Wasp infection activates immune signaling (Fig. 4)4. At the cellular level, it triggers division and differentiation of blood cells. In self defense, aggregates and capsules develop in the hemocoel of infected animals (Fig. 5)5,6. Activated blood cells migrate toward the wasp egg (or wasp larva) and begin to form a capsule around it (Fig. 5A-F). Some blood cells aggregate to form nodules (Fig. 5G-H). Careful analysis reveals that wasp infection induces the anterior-most lymph gland lobes to disperse at their peripheries (Fig. 6C, D).
We present representative data with Toll signal transduction pathway components Dorsal and Sp&auml;tzle (Figs. 4,5,7), and its target Drosomycin (Fig. 6), to illustrate how specific changes in the lymph gland and hemocoel can be studied after wasp infection. The dissection protocols described here also yield the wasp eggs (or developing stages of wasps) from the host hemolymph (Fig. 8).

An Introduction to Parasitic Wasps of Drosophila and the Antiparasite Immune Response

Parasitoid (parasitic) wasps constitute a major class of natural enemies of many insects including Drosophila melanogaster. We will introduce the techniques to propagate these parasites in Drosophila spp. and demonstrate how to analyze their effects on immune tissues of Drosophila larvae.

Most known parasitoid wasp species attack the larval or pupal stages of Drosophila. While Trichopria drosophilae infect the pupal stages of the host (Fig. ...

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 ...

Intravital Imaging of the Mouse Popliteal Lymph Node

Lymph nodes (LNs) are secondary lymphoid organs, which are strategically located throughout the body to allow for trapping and presentation of foreign antigens from peripheral tissues to prime the adaptive immune response. Juxtaposed between innate and adaptive immune responses, the LN is an ideal site to study immune cell interactions1,2. Lymphocytes (T cells, B cells and NK cells), dendritic cells (DCs), and macrophages comprise the bulk of bone marrow-derived cellular elements of the LN. These cells are strategically positioned in the LN to allow efficient surveillance of self antigens and potential foreign antigens3-5. The process by which lymphocytes successfully encounter cognate antigens is a subject of intense investigation in recent years, and involves an integration of molecular contacts including antigen receptors, adhesion molecules, chemokines, and stromal structures such as the fibro-reticular network2,6-12. 
Prior to the development of high-resolution real-time fluorescent in vivo imaging, investigators relied on static imaging, which only offers answers regarding morphology, position, and architecture. While these questions are fundamental in our understanding of immune cell behavior, the limitations intrinsic with this technique does not permit analysis to decipher lymphocyte trafficking and environmental clues that affect dynamic cell behavior. Recently, the development of intravital two-photon laser scanning microscopy (2P-LSM) has allowed investigators to view the dynamic movements and interactions of individual cells within live LNs in situ12-16. In particular, we and others have applied this technique to image cellular behavior and interactions within the popliteal LN, where its compact, dense nature offers the advantage of multiplex data acquisition over a large tissue area with diverse tissue sub-structures11,17-18. It is important to note that this technique offers added benefits over explanted tissue imaging techniques, which require disruption of blood, lymph flow, and ultimately the cellular dynamics of the system. Additionally, explanted tissues have a very limited window of time in which the tissue remains viable for imaging after explant. With proper hydration and monitoring of the animal's environmental conditions, the imaging time can be significantly extended with this intravital technique. Here, we present a detailed method of preparing mouse popliteal LN for the purpose of performing intravital imaging.

Recent advances in 2-photon microscopy have enabled real-time in situ imaging of live tissues in animal models, thereby enhancing our ability to investigate cellular behavior in both physiologic and pathologic conditions. Here, we outline the preparations required to perform intravital imaging of the mouse popliteal lymph node.

Lymph nodes (LNs) are secondary lymphoid organs, which are strategically located throughout the body to allow for trapping and presentation of foreign ...

Quantitative Measurement of the Immune Response and Sleep in Drosophila

A complex interaction between the immune response and host behavior has been described in a wide range of species. Excess sleep, in particular, is known to occur as a response to infection in mammals 1 and has also recently been described in Drosophila melanogaster2. It is generally accepted that sleep is beneficial to the host during an infection and that it is important for the maintenance of a robust immune system3,4. However, experimental evidence that supports this hypothesis is limited4, and the function of excess sleep during an immune response remains unclear. We have used a multidisciplinary approach to address this complex problem, and have conducted studies in the simple genetic model system, the fruitfly Drosophila melanogaster. We use a standard assay for measuring locomotor behavior and sleep in flies, and demonstrate how this assay is used to measure behavior in flies infected with a pathogenic strain of bacteria. This assay is also useful for monitoring the duration of survival in individual flies during an infection. Additional measures of immune function include the ability of flies to clear an infection and the activation of NF&kappa;B, a key transcription factor that is central to the innate immune response in Drosophila. Both survival outcome and bacterial clearance during infection together are indicators of resistance and tolerance to infection. Resistance refers to the ability of flies to clear an infection, while tolerance is defined as the ability of the host to limit damage from an infection and thereby survive despite high levels of pathogen within the system5. Real-time monitoring of NF&kappa;B activity during infection provides insight into a molecular mechanism of survival during infection. The use of Drosophila in these straightforward assays facilitates the genetic and molecular analyses of sleep and the immune response and how these two complex systems are reciprocally influenced.

Quantitative Measurement of the Immune Response and Sleep in Drosophila

To understand a link between the immune response and behavior, we describe a method to measure locomotor behavior in Drosophila during bacterial infection as well as the ability of flies to mount an immune response by monitoring survival, bacterial load, and real-time activity of a key regulator of innate immunity, NF&kappa;B.

A complex interaction between the immune response and  host behavior has been described in a wide range of species. Excess sleep, in  particular, is known ...

Using RNA-interference to Investigate the Innate Immune Response in Mouse Macrophages

Macrophages are key phagocytic innate immune cells. When macrophages encounter a pathogen, they produce antimicrobial proteins and compounds to kill the pathogen, produce various cytokines and chemokines to recruit and stimulate other immune cells, and present antigens to stimulate the adaptive immune response. Thus, being able to efficiently manipulate macrophages with techniques such as RNA-interference (RNAi) is critical to our ability to investigate this important innate immune cell. However, macrophages can be technically challenging to transfect and can exhibit inefficient RNAi-induced gene knockdown. In this protocol, we describe methods to efficiently transfect two mouse macrophage cell lines (RAW264.7 and J774A.1) with siRNA using the Amaxa Nucleofector 96-well Shuttle System and describe procedures to maximize the effect of siRNA on gene knockdown. Moreover, the described methods are adapted to work in 96-well format, allowing for medium and high-throughput studies. To demonstrate the utility of this approach, we describe experiments that utilize RNAi to inhibit genes that regulate lipopolysaccharide (LPS)-induced cytokine production.

In this protocol, we describe methods to efficiently transfect murine macrophage cell lines with siRNAs using the Amaxa Nucleofector 96-well Shuttle System, stimulate the macrophages with lipopolysaccharide, and monitor the effects on inflammatory cytokine production.

Macrophages are key phagocytic innate immune cells.  When macrophages encounter a pathogen, they produce antimicrobial proteins and compounds to kill the ...

In Vitro Analysis of Myd88-mediated Cellular Immune Response to West Nile Virus Mutant Strain Infection

An attenuated West Nile virus (WNV), a nonstructural (NS) 4B-P38G mutant, induced higher innate cytokine and T cell responses than the wild-type WNV in mice. Recently, myeloid differentiation factor 88 (MyD88) signaling was shown to be important for initial T cell priming and memory T cell development during WNV NS4B-P38G mutant infection. In this study, two flow cytometry-based methods &#8211; an in vitro T cell priming assay and an intracellular cytokine staining (ICS) &#8211; were utilized to assess dendritic cells (DCs) and T cell functions. In the T cell priming assay, cell proliferation was analyzed by flow cytometry following co-culture of DCs from both groups of mice with carboxyfluorescein succinimidyl ester (CFSE) - labeled CD4+ T cells of OTII transgenic mice. This approach provided an accurate determination of the percentage of proliferating CD4+ T cells with significantly improved overall sensitivity than the traditional assays with radioactive reagents. A microcentrifuge tube system was used in both cell culture and cytokine staining procedures of the ICS protocol. Compared to the traditional tissue culture plate-based system, this modified procedure was easier to perform at biosafety level (BL) 3 facilities. Moreover, WNV- infected cells were treated with paraformaldehyde in both assays, which enabled further analysis outside BL3 facilities. Overall, these in vitro immunological assays can be used to efficiently assess cell-mediated immune responses during WNV infection.

In Vitro Analysis of Myd88-mediated Cellular Immune Response to West Nile Virus Mutant Strain Infection

Two flow cytometry-based methods &#8211; an in vitro T cell priming assay and intracellular cytokine staining were utilized to measure antigen presenting capacity of dendritic cells and antigen-specific T cell responses to a West Nile virus mutant infection in mice.

An attenuated West Nile virus (WNV), a nonstructural (NS) 4B-P38G mutant, induced higher innate cytokine and T cell responses than the wild-type WNV in ...

Intravital Microscopy Imaging of the Liver following Leishmania Infection: An Assessment of Hepatic Hemodynamics

Intravital microscopy (IVM) is a powerful optical imaging technique that has made possible the visualization, monitoring and quantification of various biological events in real time and in live animals. This technology has greatly advanced our understanding of physiological processes and pathogen-mediated phenomena in specific organs.
In this study, IVM is applied to the mouse liver and protocols are designed to image in vivo the circulatory system of the liver and measure red blood cell (RBC) velocity in individual hepatic vessels. To visualize the different vessel subtypes that characterize the hepatic organ and perform blood flow speed measurements, C57Bl/6 mice are intravenously injected with a fluorescent plasma reagent that labels the liver-associated vasculature. IVM enables in vivo, real time, measurement of RBC velocity in a specific vessel of interest. Establishing this methodology will make it possible to investigate liver hemodynamics under physiological and pathological conditions. Ultimately, this imaging-based methodology will be important for studying the influence of L. donovani infection&#160;on hepatic hemodynamics.
This method can be applied to other infectious models and mouse organs and might be further extended to pre-clinical testing of a drug&#8217;s effect on inflammation by quantifying its effect on blood flow.

Intravital Microscopy Imaging of the Liver following Leishmania Infection: An Assessment of Hepatic Hemodynamics

This article reports on a detailed method for the dynamic measurement and quantification of blood flow velocity within individual blood vessels of the mouse liver vasculature using intravital microscopy imaging in combination with a specific methodology for image acquisition and analysis.

Intravital microscopy (IVM) is a powerful optical imaging technique that has made possible the visualization, monitoring and quantification of various ...

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, ...

Non-invasive Imaging of the Innate Immune Response in a Zebrafish Larval Model of Streptococcus iniae Infection

The aquatic pathogen, Streptococcus iniae, is responsible for over 100 million dollars in annual losses for the aquaculture industry and is capable of causing systemic disease in both fish and humans. A better understanding of S. iniae disease pathogenesis requires an appropriate model system. The genetic tractability and the optical transparency of the early developmental stages of zebrafish allow for the generation and non-invasive imaging of transgenic lines with fluorescently tagged immune cells. The adaptive immune system is not fully functional until several weeks post fertilization, but zebrafish larvae have a conserved vertebrate innate immune system with both neutrophils and macrophages. Thus, the generation of a larval infection model allows the study of the specific contribution of innate immunity in controlling S. iniae infection.
The site of microinjection will determine whether an infection is systemic or initially localized. Here, we present our protocols for otic vesicle injection of zebrafish aged 2-3 days post fertilization as well as our techniques for fluorescent confocal imaging of infection. A localized infection site allows observation of initial microbe invasion, recruitment of host cells and dissemination of infection. Our findings using the zebrafish larval model of S. iniae infection indicate that zebrafish can be used to examine the differing contributions of host neutrophils and macrophages in localized bacterial infections. In addition, we describe how photolabeling of immune cells can be used to track individual host cell fate during the course of infection.

Non-invasive Imaging of the Innate Immune Response in a Zebrafish Larval Model of Streptococcus iniae Infection

Here, we present a protocol for the generation and imaging of a localized bacterial infection in the zebrafish otic vesicle.

The aquatic pathogen, Streptococcus iniae, is responsible for over 100 million dollars in annual losses for the aquaculture industry and is capable of ...

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 ...