The authors would like to thank the GI and Liver Innate Immune Programs for monetary support of this project. B.A.J.T. is also funded by R01 AI121209.

All methods described here have been approved by the Institutional Animal Care and Use Committee (IACUC) of the University of Colorado Anschutz Medical Campus.
1.&#160;Preparation of the Materials
<ol>
	<li>Make a 5 mg/mL solution of DNase I in phosphate-buffered saline (PBS).</li>
	<li>Make a digestion mixture by adding 5,000 U/mL of collagenase IV to Click&#8217;s EHAA media.</li>
	<li>Warm the digestion mixture at 37 &#176;C for 30 min prior to use.</li>
...

<ol>
	<li>Tanaka, M., Iwakiri, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lymphatics+in+the+liver.">Lymphatics in the liver.</a> Current Opinion in Immunology. 53, 137-142 (2018).</li><li>Vollmar, B., Wolf, B., Siegmund, S., Katsen, A. D., 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=Lymph+vessel+expansion+and+function+in+the+development+of+hepatic+fibrosis+and+cirrhosis.">Lymph vessel expansion and function in the development of hepatic fibrosis and cirrhosis.</a> The American Journal of Pathology. 151 (1), 169-175 (1997).</li><li>Podgrabinska, 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=Molecular+characterization+of+lymphatic+endothelial+cells.">Molecular characterization of lymphatic endothelial cells.</a> Proceedings of the National Academy of Sciences of the United States of America. 99 (25), 16069-16074 (2002).</li><li>Cohen, J. 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=Lymph+node-resident+lymphatic+endothelial+cells+mediate+peripheral+tolerance+via+Aire-independent+direct+antigen+presentation.">Lymph node-resident lymphatic endothelial cells mediate peripheral tolerance via Aire-independent direct antigen presentation.</a> Journal of Experimental Medicine. 207 (4), 681-688 (2010).</li><li>Cohen, J. 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=Tolerogenic+properties+of+lymphatic+endothelial+cells+are+controlled+by+the+lymph+node+microenvironment.">Tolerogenic properties of lymphatic endothelial cells are controlled by the lymph node microenvironment.</a> PLoS One. 9 (2), e87740 (2014).</li><li>Rouhani, S. J., 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=Roles+of+lymphatic+endothelial+cells+expressing+peripheral+tissue+antigens+in+CD4+T-cell+tolerance+induction.">Roles of lymphatic endothelial cells expressing peripheral tissue antigens in CD4 T-cell tolerance induction.</a> Nature Communications. 6, 6771 (2015).</li><li>Tewalt, E. 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=Lymphatic+endothelial+cells+induce+tolerance+via+PD-L1+and+lack+of+costimulation+leading+to+high-level+PD-1+expression+on+CD8+T+cells.">Lymphatic endothelial cells induce tolerance via PD-L1 and lack of costimulation leading to high-level PD-1 expression on CD8 T cells.</a> Blood. 120 (24), 4772-4782 (2012).</li><li>Dubrot, J., 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=Lymph+node+stromal+cells+acquire+peptide-MHCII+complexes+from+dendritic+cells+and+induce+antigen-specific+CD4(+)+T+cell+tolerance.">Lymph node stromal cells acquire peptide-MHCII complexes from dendritic cells and induce antigen-specific CD4(+) T cell tolerance.</a> Journal of Experimental Medicine. 211 (6), 1153-1166 (2014).</li><li>Hirosue, 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=Steady-state+antigen+scavenging,+cross-presentation,+and+CD8++T+cell+priming:+a+new+role+for+lymphatic+endothelial+cells.">Steady-state antigen scavenging, cross-presentation, and CD8+ T cell priming: a new role for lymphatic endothelial cells.</a> Journal of Immunology. 192 (11), 5002-5011 (2014).</li><li>Lund, A. W., 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=VEGF-C+promotes+immune+tolerance+in+B16+melanomas+and+cross-presentation+of+tumor+antigen+by+lymph+node+lymphatics.">VEGF-C promotes immune tolerance in B16 melanomas and cross-presentation of tumor antigen by lymph node lymphatics.</a> Cell Reports. 1 (3), 191-199 (2012).</li><li>Lund, A. W., 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=Lymphatic+vessels+regulate+immune+microenvironments+in+human+and+murine+melanoma.">Lymphatic vessels regulate immune microenvironments in human and murine melanoma.</a> Journal of Clinical Investigation. 126 (9), 3389-3402 (2016).</li><li>Swartz, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunomodulatory+roles+of+lymphatic+vessels+in+cancer+progression.">Immunomodulatory roles of lymphatic vessels in cancer progression.</a> Cancer Immunology Research. 2 (8), 701-707 (2014).</li><li>Dietrich, T., 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=Cutting+edge:+lymphatic+vessels,+not+blood+vessels,+primarily+mediate+immune+rejections+after+transplantation.">Cutting edge: lymphatic vessels, not blood vessels, primarily mediate immune rejections after transplantation.</a> Journal of Immunology. 184 (2), 535-539 (2010).</li><li>Kedl, 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=Migratory+Dendritic+Cells+acquire+archived+antigen+from+Lymphatic+Endothelial+Cells+for+antigen+presentation+during+lymph+node+contraction.">Migratory Dendritic Cells acquire archived antigen from Lymphatic Endothelial Cells for antigen presentation during lymph node contraction.</a> Nature Communications. 8, 2034 (2017).</li><li>Kedl, R. M., Tamburini, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antigen+archiving+by+lymph+node+stroma:+A+novel+function+for+the+lymphatic+endothelium.">Antigen archiving by lymph node stroma: A novel function for the lymphatic endothelium.</a> European Journal of Immunology. 45 (10), 2721-2729 (2015).</li><li>Tamburini, B. A., Burchill, M. A., Kedl, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antigen+capture+and+archiving+by+lymphatic+endothelial+cells+following+vaccination+or+viral+infection.">Antigen capture and archiving by lymphatic endothelial cells following vaccination or viral infection.</a> Nature Communications. 5, 3989 (2014).</li><li>Yokomori, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lymphatic+marker+podoplanin/D2-40+in+human+advanced+cirrhotic+liver--re-evaluations+of+microlymphatic+abnormalities.">Lymphatic marker podoplanin/D2-40 in human advanced cirrhotic liver--re-evaluations of microlymphatic abnormalities.</a> BMC Gastroenterology. 10, 131 (2010).</li><li>Nonaka, H., Tanaka, M., Suzuki, K., Miyajima, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+murine+hepatic+sinusoidal+endothelial+cells+characterized+by+the+expression+of+hyaluronan+receptors.">Development of murine hepatic sinusoidal endothelial cells characterized by the expression of hyaluronan receptors.</a> Developmental Dynamics. 236 (8), 2258-2267 (2007).</li><li>Dudas, J., 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=Prospero-related+homeobox+1+(Prox1)+is+a+stable+hepatocyte+marker+during+liver+development,+injury+and+regeneration,+and+is+absent+from+"oval+cells".">Prospero-related homeobox 1 (Prox1) is a stable hepatocyte marker during liver development, injury and regeneration, and is absent from "oval cells".</a> Histochemistry and Cell Biology. 126 (5), 549-562 (2006).</li><li>Schrage, A., 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=Murine+CD146+is+widely+expressed+on+endothelial+cells+and+is+recognized+by+the+monoclonal+antibody+ME-9F1.">Murine CD146 is widely expressed on endothelial cells and is recognized by the monoclonal antibody ME-9F1.</a> Histochemistry and Cell Biology. 129 (4), 441-451 (2008).</li><li>Amatschek, 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=Blood+and+lymphatic+endothelial+cell-specific+differentiation+programs+are+stringently+controlled+by+the+tissue+environment.">Blood and lymphatic endothelial cell-specific differentiation programs are stringently controlled by the tissue environment.</a> Blood. 109 (11), 4777-4785 (2007).</li><li>Huang, L., Soldevila, G., Leeker, M., Flavell, R., Crispe, I. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+liver+eliminates+T+cells+undergoing+antigen-triggered+apoptosis+in+vivo.">The liver eliminates T cells undergoing antigen-triggered apoptosis in vivo.</a> Immunity. 1 (9), 741-749 (1994).</li><li>Shay, T., Kang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunological+Genome+Project+and+systems+immunology.">Immunological Genome Project and systems immunology.</a> Trends in Immunology. 34 (12), 602-609 (2013).</li><li>Li, B., 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=Adult+Mouse+Liver+Contains+Two+Distinct+Populations+of+Cholangiocytes.">Adult Mouse Liver Contains Two Distinct Populations of Cholangiocytes.</a> Stem Cell Reports. 9 (2), 478-489 (2017).</li><li>Randolph, G. J., Ivanov, S., Zinselmeyer, B. H., Scallan, J. 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+Lymphatic+System:+Integral+Roles+in+Immunity.">The Lymphatic System: Integral Roles in Immunity.</a> Annual Review of Immunology. 35, 31-52 (2016).</li><li>Olszewski, W. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+lymphatic+system+in+body+homeostasis:+physiological+conditions.">The lymphatic system in body homeostasis: physiological conditions.</a> Lymphatic Research and Biology. 1 (1), 11-21 (2003).</li></ol>

The authors have nothing to disclose.

The overall importance of LECs in immune homeostasis and regulation has recently come to light25. Much of the published lymphatic literature focuses on skin and lymph nodes; however, lymphatics are found throughout the body26 and, thus, our understanding of their importance in different organs is needed. Here we show a method in which LECs in the liver can be studied on a cell-by-cell basis to better understand their concurrent expression of different surface markers, cytok...

The role of lymphatic vessels and LECs in the liver is not well understood. While lymphatic vessels are found within the portal triad of the liver1 and expand during disease2, very little is understood regarding the function and phenotype of LECs within the liver. With the discovery of markers that are found primarily on LECs3, the importance of these cells within different tissue niches in homeostasis and disease will fill a significant gap in our understanding. LECs have a major role in maintaining peripheral tolerance in the lymph node and in metastatic tumors by interacting directly with T cells4,5,6,7,8,9,10,11,12,13. LECs in the lymph node can promote protective immunity via their interactions with migratory dendritic cells14,15,16. Therefore, there are multiple roles for LECs which may be specific to the tissues and interactions in which they are present. However, very little is understood about how LECs interact with immune cells in the tissue or how LECs function in different organ systems; thus, evaluating LECs on a per cell basis within the liver or other organs may lead to advances in how LECs program tissue-specific immunity. While much of the literature that focuses on LECs in the liver uses microscopy to visualize LECs using one or two markers and morphology17, very little has been done to specifically evaluate LECs on a cell by cell basis using flow cytometry, though one study did evaluate differences between liver sinusoidal endothelial cells (LSECs) and LECs18. Being able to analyze LEC populations in the liver by flow cytometry allows for the in-depth study of LEC phenotype during normal homeostasis or disease.
To evaluate LECs by flow cytometry, multiple surface markers are needed. Typically, LECs are visualized by the expression of prospero-related homeobox 1 (Prox-1), lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1) or vascular endothelial growth factor receptor 3 (VEGFR3) using microscopy. However, in the liver, the expression of these markers is not restricted to LECs. Prox-1 is widely expressed by hepatocytes during liver development, regeneration, and injury19, and LYVE1 and VEGFR3 are expressed by the liver sinusoidal endothelial cells18. In the lymph node, LECs are identified using flow cytometry as clusters of differentiation (CD) CD45-, CD31+, and podoplanin+ (PDPN)16. However, this approach is too minimal to isolate LECs in the liver since CD45- CD31+ cells will capture endothelial cells, and the predominant population of vascular endothelial cells in the liver are LSECs. Thus, other markers are needed to distinguish the rare LEC population from the abundant LSEC population. Both CD16/32 (expressed by mature LSECs18) and CD146 (a common vascular endothelial cell marker that is predominately expressed within the liver sinusoids by liver sinusoidal endothelial cells20 with little to no expression by lymphatic endothelial cells21) were candidate markers.
Therefore, we optimized a method for isolating and visualizing LECs in the liver using the above markers, CD45, CD31, CD146, CD16/32, and PDPN for flow cytometry. We describe the use of collagenase IV, DNase 1, and mechanical separation for liver tissue digestion into a single-cell suspension. We also describe the use of iodixanol density gradient for the isolation of non-parenchymal cells (NPC) and to eliminate cellular debris. Finally, using multiple markers, we determine the optimal flow cytometry gating strategy to identify LECs from the liver with PDPN as the predominant marker.

<table>
	<tbody>
		<tr>
			<td>Clicks/EHAA media</td>
			<td>Irvine Scientific</td>
			<td>9195</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase IV</td>
			<td>Worthington Biochemical corporation</td>
			<td>LS004188</td>
			<td></td>
		</tr>
		<tr>
			<td>DNase I</td>
			<td>Worthington Biochemical corporation</td>
			<td>LS002145</td>
			<td>Deoxyribonuclease 1</td>
		</tr>
		<tr>
			<td>OptiPrep</td>
			<td>Sigma Aldrich</td>
			<td>D1556</td>
			<td>Density Gradient Medium</td>
		</tr>
		<tr>
			<td>V450 anti mouse CD146(clone ME-9F1</td>
			<td>BD biosciences</td>
			<td>562232</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC anti mouse CD146 (clone ME-9F1</td>
			<td>Biolegend</td>
			<td>134706</td>
			<td>Fluorescein isothiocyanate (FITC)</td>
		</tr>
		<tr>
			<td>Pacific Blue anti mouse CD31(clone 390)</td>
			<td>Biolegend</td>
			<td>102422</td>
			<td></td>
		</tr>
		<tr>
			<td>PerCp/Cy5.5 anti mouse CD31( clone 390)</td>
			<td>Biolegend</td>
			<td>102420</td>
			<td>Peridinin-chlorophyll proteins-Cyanine 5.5 (PerCP-Cy5.5)</td>
		</tr>
		<tr>
			<td>APC anti mouse PDPN (clone 8.1.1)</td>
			<td>Biolegend</td>
			<td>127410</td>
			<td>Allophycocyanin (APC), podoplanin (PDPN)</td>
		</tr>
		<tr>
			<td>APC/Cy7 anti mouse CD45 (clone 30-F11)</td>
			<td>Biolegend</td>
			<td>103116</td>
			<td></td>
		</tr>
		<tr>
			<td>Brilliant Violet 510 anti mouse CD45 (clone 30-F11</td>
			<td>Biolegend</td>
			<td>103138</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC anti mouse CD16/32 (clone 93)</td>
			<td>Biolegend</td>
			<td>101306</td>
			<td>Fluorescein isothiocyanate (FITC)</td>
		</tr>
		<tr>
			<td>PerCp/Cy5.5 anti mouse CD16/32( clone 93)</td>
			<td>Biolegend</td>
			<td>101324</td>
			<td>Peridinin-chlorophyll proteins-Cyanine 5.5 (PerCP-Cy5.5)</td>
		</tr>
		<tr>
			<td>ghost red 780 viability dye</td>
			<td>TONBO biosceinces</td>
			<td>3-0865-T100</td>
			<td></td>
		</tr>
		<tr>
			<td>APC syrian hamster IgG (clone SHG-1)</td>
			<td>Biolegened</td>
			<td>402102</td>
			<td></td>
		</tr>
		<tr>
			<td>PerCp/Cy5.5 rat IgG2a (clone RTK2758)</td>
			<td>Biolegend</td>
			<td>400531</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC rat IgG2 (clone eBR2a)</td>
			<td>ebioscience</td>
			<td>1-4321-80</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti mouse LYVE1 (clone 223322)</td>
			<td>R&#38;D systems</td>
			<td>FAB2125A</td>
			<td></td>
		</tr>
		<tr>
			<td>anti-mouse Cytokeratin(clone EPR17078)</td>
			<td>abcam</td>
			<td>ab181598</td>
			<td></td>
		</tr>
		<tr>
			<td>anti-mouse F4/80 (clone Cl:A3-1)</td>
			<td>Bio-rad</td>
			<td>MCA497</td>
			<td></td>
		</tr>
		<tr>
			<td>BSA (fraction V)</td>
			<td>Fischer</td>
			<td>BP1600-100</td>
			<td>Bovine Serum Albumin (BSA)</td>
		</tr>
		<tr>
			<td>Goat serum</td>
			<td>Jackson Immunoresearch</td>
			<td>017-000-121</td>
			<td></td>
		</tr>
		<tr>
			<td>Donkey Serum</td>
			<td>Jackson Immunoresearch</td>
			<td>017-000-121</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>VWR</td>
			<td>E177</td>
			<td>Ethylenediaminetetraacetic acid (EDTA) -for RBC lysis buffer</td>
		</tr>
		<tr>
			<td>Ammonium Chloride</td>
			<td>Fischer</td>
			<td>A687-500</td>
			<td>for RBC Lysis buffer</td>
		</tr>
		<tr>
			<td>Potassium Bicarbonate</td>
			<td>Fischer</td>
			<td>P184-500</td>
			<td>for RBC Lysis buffer</td>
		</tr>
		<tr>
			<td>Scalpel</td>
			<td>Feather</td>
			<td>2975#21</td>
			<td></td>
		</tr>
		<tr>
			<td>100um cell strainer</td>
			<td>Fischer</td>
			<td>22363549</td>
			<td></td>
		</tr>
		<tr>
			<td>2.4G2</td>
			<td>in house/ATCC</td>
			<td>ATCC HB-197</td>
			<td>FC block to inhibit non-specific binding to Fc gamma + cells -made from hybridoma</td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline (PBS)</td>
			<td>Corning</td>
			<td>21-040-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Hanks Balanced Salt Solution (HBSS)</td>
			<td>Gibco</td>
			<td>14185-052</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum (FBS)</td>
			<td>Atlanta biologicals</td>
			<td>S11550</td>
			<td></td>
		</tr>
		<tr>
			<td>96 well plate</td>
			<td>Corning</td>
			<td>3788</td>
			<td></td>
		</tr>
		<tr>
			<td>6 well plate</td>
			<td>Corning</td>
			<td>3506</td>
			<td></td>
		</tr>
		<tr>
			<td>50 ml conical</td>
			<td>Truline</td>
			<td>TR2004</td>
			<td></td>
		</tr>
		<tr>
			<td>15 ml conical</td>
			<td>Falcon</td>
			<td>352196</td>
			<td></td>
		</tr>
		<tr>
			<td>1 ml Pipete tip</td>
			<td>USA scientific</td>
			<td>1111-2721</td>
			<td></td>
		</tr>
		<tr>
			<td>200 &#181;l pipete tip</td>
			<td>USA scientific</td>
			<td>1110-1700</td>
			<td></td>
		</tr>
		<tr>
			<td>10 &#181;l pipete tip</td>
			<td>USA scientific</td>
			<td>1111-3700</td>
			<td></td>
		</tr>
		<tr>
			<td>seriological 10ml pipete</td>
			<td>greiner bio-one</td>
			<td>607107</td>
			<td></td>
		</tr>
		<tr>
			<td>seriological 5ml pipete</td>
			<td>greiner bio-one</td>
			<td>606107</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell incubator</td>
			<td>Fischer</td>
			<td></td>
			<td>Heracell 160i</td>
		</tr>
		<tr>
			<td>BD FacsCanto II flow cytometer</td>
			<td>BD biosciences</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Clinical Centrifuge</td>
			<td>Beckman coulter</td>
			<td></td>
			<td>model X-14R</td>
		</tr>
	</tbody>
</table>

digestion of the murine liver for a flow cytometric analysis of lymphatic endothelial cells

Within the liver, lymphatic vessels are found within the portal triad, and their described function is to remove interstitial fluid from the liver to the lymph nodes where cellular debris and antigens can be surveyed. We are very interested in understanding how the lymphatic vasculature might be involved in inflammation and immune cell function within the liver. However, very little has been published establishing digestion protocols for the isolation of lymphatic endothelial cells (LECs) from the liver or specific markers that can be used to evaluate liver LECs on a per cell basis. Therefore, we optimized a method for the digestion and staining of the liver in order to evaluate the LEC population in the liver. We are confident that the method outlined here will be useful for the identification and isolation of LECs from the liver and will strengthen our understanding of how LECs respond to the liver microenvironment.

Studies analyzing liver lymphatics have primarily used immunohistochemistry to quantitate the frequency and diameter of lymphatic vessels in the liver. However, this method does not allow for the evaluation of LECs on a cell-by-cell basis or for expression of multiple markers, cytokines, chemokines, or transcription factors. Therefore, we asked whether liver LECs could be isolated from the liver and evaluated using flow cytometry. Previous work isolating lymph node LECs was performed usin...

Watch this Scientific Journal Video about Digestion of the Murine Liver for a Flow Cytometric Analysis of Lymphatic Endothelial Cells at JoVE.com

Digestion of the Murine Liver for a Flow Cytometric Analysis of Lymphatic Endothelial Cells

The goal of this protocol is to identify lymphatic endothelial cell populations within the liver using described markers. We utilize collagenase IV and DNase and a gentle mincing of tissue, combined with flow cytometry, to identify a distinct population of lymphatic endothelial cells.

Within the liver, lymphatic vessels are found within the portal triad, and their described function is to remove interstitial fluid from the liver to the ...

This method can help answer key questions in lymphatic and liver fields, such as how lymphatic endothelial cells, or LECs, respond to specific stimuli and how that contributes to disease pathogenesis. The main advantage of this technique is that we can evaluate liver lymphatic endothelial cell phenotype and function on a per cell basis, and can be used for down-stream applications after cell sorting. Though this method can provide insight into liver lymphatic biology, it can also be used to evaluate lymphatic endothelial cells from different tissues, such as skin and mammary gland.Demonstrating the procedure will be Jeffrey Finlon, a professional research assistant from my laboratory. To prepare a single-cell suspension from isolated liver cells, begin by spraying down the mouse with seventy-percent ethanol, and securing the paws to a dissection board. Use dissection scissors to cut the skin about one centimeter above the anus and use toothed forceps to lift the skin away from the body.Insert the scissor tips between the skin and the peritoneum and open the scissors to separate the tissues before continuing the skin incision up to the neck. Secure the skin to the dissection board under each forelimb and above each hindlimb, and pull the peritoneal sack upward to extend the incision toward the neck. Grasp the lobes of the liver and cut just below the sternum to allow dissection around the liver.Then transfer the organ into four milliliters of Click's EHAA medium. Use the scalpel to cut the liver into approximately one-millimeter diameter pieces and digest the pieces in five hundred microliters of freshly prepared digestion solution and five hundred microliters of DNase 1. After fifteen minutes at thirty-seven degrees Celsius, use a five hundred milliliter pipet to mix the tissues thoroughly and return the container to the incubator for another fifteen minutes.At the end of the incubation, transfer the digested sample through a one hundred micron strainer into a fifty milliliter conical tube and use the plunger from a one milliliter syringe to gently press the remaining pieces of tissue through the mesh. Wash the filter with five milliliters of isolation buffer and gently press any remaining tissue through the strainer. Collect the isolated liver cells by centrifugation and re-suspend the pellet in four milliliters of red blood cell lysis buffer.After five minutes at room temperature, wash the cells in ten milliliters of isolation buffer and count the cells on the hemocytometer to determine the full liver count. Re-suspend the pellet in five milliliters of twenty-percent iodixanol and overlay the cell suspension with one milliliter of PBS. Separate the cells by density gradient separation and harvest the layer between the PBS and the iodixanol.Then filter the cells through a one hundred micrometer strainer into a new fifty milliliter conical tube. Wash the cells in ten milliliters of fresh isolation buffer and re-suspend the resulting pellet in five hundred microliters of PBS, supplemented with two-percent fetal bovine serum, or FBS. After counting, aliquot approximately five times ten to the sixth non-parenchymal cells into each control and experimental well of a ninety-six well plate for centrifugation and re-suspend the pellets in ninety microliters of PBS plus FBS per well.Add the appropriate experimental and control primary antibody cocktails to each well and stain all of the wells with an appropriate viability marker. The most important step in this procedure is the proper titration of the antibodies and the use of ice type controls and fluorescence-1 controls to validate the staining. After thirty minutes at four degrees Celsius, centrifuge wash the cells with one hundred microliters of PBS plus FBS per well and transfer the cells from each well into individual five milliliter round-bottom flow cytometry tubes to a four hundred microliter final volume of PBS plus FBS per tube.Then, use a small volume of cells to adjust the laser and compensation settings on the flow cytometer and read all of the events for each tube. When all of the tubes have been read, import the data into an appropriate flow cytometry analysis program. Gate on live cells based on the viability marker dye where negative expression is considered live.Gate on the live cells based on the size and granularity of the cells as well as their viability marker dye expression, followed by gating on the CD45 negative CD31 positive cell population using the appropriate isotype control and fluorescence-1 data to determine the positive and negative populations. Then gate the CD45 negative CD31 positive cells according to their CD16/32 and podoplanin expression to allow identification of the CD45 negative CD31 positive, CD16/32 negative podoplanin positive lymphatic endothelial, and CD45 negative CD31 positive, CD16/32 positive podoplanin negative liver sinusoidal endothelial cell populations. Emphatic endothelial cells express lymphatic vessel and endothelial hyaluronan one, but not CD146.Liver isolated CD31 positive CD16/32 positive cells isolated as demonstrated are also CD146 positive and podoplanin positive, while the CD31 positive CD16/32 negative cells are primarily CD146 negative and either podoplanin positive or negative. Positivity was determined based on fluorescence-1 staining. The liver lymphatic endothelial cells are CD146 negative and PDPN positive.Neither the vascular endothelium nor murine liver macrophages express podoplanin. Podoplanin staining can also be used to distinguish cholangiocytes from lymphatic vessels based on the distinct nuclear structures of the bile ducts as well as by cytokeratin 7 staining. As only lymphatic endothelial cells co-express vascular endothelial growth factor receptor 3 and Prospero homeobox protein 1 in the liver, these markers can be further used to confirm the purity of the sorted liver lymphatic endothelial cell population.While attempting this procedure, it is important to remember to work quickly and keep cells on ice. Following this procedure, other methods like flow sorting of LEC populations can be performed in order to answer additional questions, such as transcriptional profiling of LECs. After its development, this technique paved the way for researchers in the field of liver-specific lymphatic biology to explore how lymphatics impact liver disease in mice and humans.Generally, individuals new to this method will struggle because lymphatic endothelial cells are an infrequent, gradual population in a liver and the method needs to be performed quickly.

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JoVE Journal

Immunology and Infection

10.5K vues.  University of Colorado Anschutz Medical Campus, School of Medicine. Cette méthode peut aider à répondre à des questions clés dans les domaines lymphatiques et hépatiques, tels que la façon dont les cellules endothéliales lymphatiques, ou LEC, répondent à des stimuli spécifiques et comment cela contribue à la pathogénie de la maladie. Le principal avantage de cette technique est que nous pouvons évaluer le phénotype et la fonction des cellules endothéliales lymphatiques hépatiques sur une base par cellule, et peut être utilisé pour des appli...