The authors thank Ava Zardynezhad for proofreading of the manuscript. This work is supported by the Canadian Institute of Health Research (CIHR, PJT-156035), and the Canada Foundation for Innovation for SL (32930), and by the National Natural Science Foundation of China for Yujia Lin (81901576).

All animal work needs to be approved by institutional and governmental ethics and animal handling committee.&#160; This is a non-survival surgery.&#160;
1. Preparation of materials
<ol>
	<li>Prepare 100 mL of 70% ethanol by mixing 70 mL of 100% ethanol with 30 mL of sterile water. Autoclave all surgical tools before surgery and keep the tools in 70% ethanol before and during the surgery to maintain sterilization.</li>
	<li>Prepare an injection apparatus.
	<ol>
		<li>Cut ~30 cm of polyethylene tubing (0.28 mm in diameter). Connect the tip of a 30 G x &#189; needle (needle A) to one end of polyethylene tubing. Carefully dislodge another 30 G x &#189; needle (needle B) and connect the broken side to the other end of polyethylene tubing.</li>
		<li>Attach needle A to a 1 mL tuberculin syringe. 
		NOTE: For this polyethylene tubing, 1.6 cm of fluid in the tubing corresponds to 1 &#956;L20.</li>
	</ol>
	</li>
	<li>Prepare a 10:1 ketamine/xylazine mixture (10 mg/mL ketamine and 1 mg/mL xylazine) in saline (bacteriostatic 0.9% [w/v] sodium chloride). Prepare the solution freshly before use.</li>
</ol>
2. Preparation of the animal for surgery
NOTE: Use mice aged 6&#8722;10 weeks. Both female and male mice can be used. In this study, 6&#8722;10-week-old, C57BL/6 female mice were used. This method can be adapted for other strains of mice.
<ol>
	<li>Anesthetize the mouse by injecting 250 &#956;L of the ketamine/xylazine mixture intraperitoneally. Wait until the mouse is completely asleep. Ensure mouse does not react to a toe pinch to detect full anesthetization.</li>
	<li>Shave fur around the legs with hair clippers.</li>
	<li>Apply the depilatory cream around the leg and wait for 5 min. Wipe off the residual fur and the depilatory cream using a moist tissue and clean the leg with sterile water. Spray 70% ethanol around the leg to sterilize the operating area. The ethanol is restricted to the incision site.&#160;</li>
</ol>
3. Surgical suturing of afferent lymphatic vessels
NOTE: The right leg is sutured, and the left leg is used as the sham control. The lymphatic suture protocol (steps 3.1&#8722;3.8) takes 20&#8722;30 min.
<ol>
	<li>Keep mouse at a prone position and fix it with surgical tape to expose the operation area on the right leg.</li>
	<li>Intradermally inject 5 &#181;L of 1% Evans blue dye or 9 cm of the fluid of the injection apparatus tubing into the footpad. Gently massage the footpad to help Evans blue enter the lymphatic vessels. 
	NOTE: The insulin syringe is not easy to control for small volume injection. The volume can be controlled more accurately using the injection apparatus. Lymphatic vessels are visualized by blue dye under the skin. With extensive training, both afferent lymphatic vessels can be seen with the naked eye as transparent vessels in the adipose tissue, parallel to the Saphenous artery. With extensive training, it is possible to suture the vessels without injecting Evans Blue dye in cases where there are concerns of potential disturbances from the dye.</li>
	<li>Under a dissecting microscope, choose an incision site 5 mm from the bottom edge of the popliteal fossa. Make a small incision (~5 mm) in the skin with scissors. Using fine operation forceps, stretch the incision, and expose the collecting lymphatic vessels (Figure 1A). 
	NOTE: If necessary, a small skin fragment can be removed to expose the lymphatic vessels.</li>
	<li>Identify both afferent lymphatic vessels leading to the pLNs under the dissecting microscope (Figure 1B). 
	NOTE: There are two afferent lymphatic vessels from the footpad to the pLN. Both need to be sutured to block lymph flow completely.</li>
	<li>Using a needle holder, cautiously insert the suture needle (0.7 metric or smaller) between the afferent lymphatic vessel and the Saphenous artery and pull the needle gently out around the afferent lymphatic vessel. Gently pull the suture string and leave about 2 cm of the suture string behind. Use the needle holder to help tie the string tightly to suture one lymphatic vessel with a surgeon&#8217;s knot (Figure 1C). 
	NOTE: The tissue underneath the incision may dry out with prolonged exposure to air. Making the incision as small as possible and performing the suture quickly (i.e., within 5 min) will prevent the tissue from drying out. Maintain the tissue moisture by applying a small volume of saline with a cotton swab.</li>
	<li>Gently massage the footpad to ensure no Evans Blue dye passes the suture site and then cut the excess string with scissors.</li>
	<li>Perform the same suture steps (i.e., steps 3.5 and 3.6) on the other afferent lymphatic vessel (Figure 1D). Close the skin incision with the same suture that was used to suture the vessels in step 3.5 (Figure 1E).</li>
	<li>For the sham control, intradermally inject 5 &#181;L of 1% Evans blue dye at the left footpad and massage the footpad to visualize the lymphatic vessels. Open the skin with an excision and then close the wound without suturing the vessel (Figure 1F).</li>
	<li>Optionally, monitor the operated mice for 2&#8722;4 h. The suture side of the leg should show edema with Evans Blue spread to the thigh, while the control leg will show restricted Evans blue dye in the footpad.&#160;If mice&#160;awaken, an additional ketamine/xylazine&#160;mix will be injected to keep anesthetized until euthanasia.</li>
</ol>
4. Tracking of the lymph flow
<ol>
	<li>Immediately after the surgery, intradermally inject 10 &#181;L of 2% fluorescein isothiocyanate (FITC) in the footpad of both the control and the lymphatic sutured leg.</li>
	<li>Euthanize the mice with 400 &#956;L of ketamine/xylazine mixture and perform cervical dislocation when the mice are fully anesthetized.</li>
	<li>Collect pLNs from the popliteal fossa and carefully remove the perinodal adipose tissue around the pLNs under the dissection microscope at 2, 6, and 12 h after FITC injection.</li>
	<li>Embed the pLNs with the medullary sinus area facing to the side of the cryomold in optimal cutting temperature (OCT) compound (Figure 1G,H).</li>
	<li>Prepare 20 &#181;m frozen sections using a cryotome.</li>
	<li>Image the cryosections under a confocal microscope to determine FITC distribution.</li>
</ol>

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W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+morphological+evidence+for+a+mechanism+of+lymph+formation+in+skeletal+muscle.">New morphological evidence for a mechanism of lymph formation in skeletal muscle.</a> Microvascular Research. 28, 95-112 (1984).</li><li>Johnston, M. G., Hay, J. B., Movat, H. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetics+of+prostaglandin+production+in+various+inflammatory+lesions,+measured+in+draining+lymph.">Kinetics of prostaglandin production in various inflammatory lesions, measured in draining lymph.</a> The American Journal of Pathology. 95, 225-238 (1979).</li><li>Eisenhoffer, J., Yuan, Z. Y., Johnston, M. 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P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dendritic+cells+control+lymphocyte+entry+to+lymph+nodes+through+high+endothelial+venules.">Dendritic cells control lymphocyte entry to lymph nodes through high endothelial venules.</a> Nature. 479, 542-546 (2011).</li><li>Gretz, J. E., Norbury, C. C., Anderson, A. O., Proudfoot, A. E., Shaw, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lymph-borne+chemokines+and+other+low+molecular+weight+molecules+reach+high+endothelial+venules+via+specialized+conduits+while+a+functional+barrier+limits+access+to+the+lymphocyte+microenvironments+in+lymph+node+cortex.">Lymph-borne chemokines and other low molecular weight molecules reach high endothelial venules via specialized conduits while a functional barrier limits access to the lymphocyte microenvironments in lymph node cortex.</a> The Journal of Experimental Medicine. 192, 1425-1440 (2000).</li><li>Mebius, R. E., Breve, J., Duijvestijn, A. M., Kraal, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+function+of+high+endothelial+venules+in+mouse+lymph+nodes+stimulated+by+oxazolone.">The function of high endothelial venules in mouse lymph nodes stimulated by oxazolone.</a> Immunology. 71, 423-427 (1990).</li><li>Mebius, R. E., Streeter, P. R., Breve, J., Duijvestijn, A. M., Kraal, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+afferent+lymphatic+vessel+interruption+on+vascular+addressin+expression.">The influence of afferent lymphatic vessel interruption on vascular addressin expression.</a> Journal of Cell Biology. 115, 85-95 (1991).</li><li>Mebius, R. 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=Expression+of+GlyCAM-1,+an+endothelial+ligand+for+L-selectin,+is+affected+by+afferent+lymphatic+flow.">Expression of GlyCAM-1, an endothelial ligand for L-selectin, is affected by afferent lymphatic flow.</a> Journal of Immunology. 151, 6769-6776 (1993).</li><li>Drayton, D. L., Liao, S., Mounzer, R. H., Ruddle, N. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lymphoid+organ+development:+from+ontogeny+to+neogenesis.">Lymphoid organ development: from ontogeny to neogenesis.</a> Nature Immunology. 7, 344-353 (2006).</li><li>Tomei, A. A., Siegert, S., Britschgi, M. R., Luther, S. A., Swartz, M. 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P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+for+the+quantitative+measurement+of+collecting+lymphatic+vessel+contraction+in+mice.">Method for the quantitative measurement of collecting lymphatic vessel contraction in mice.</a> Journal of Biological Methods. 1, 6 (2014).</li><li>Lin, Y., 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=Perinodal+Adipose+Tissue+Participates+in+Immune+Protection+through+a+Lymphatic+Vessel-Independent+Route.">Perinodal Adipose Tissue Participates in Immune Protection through a Lymphatic Vessel-Independent Route.</a> Journal of Immunology. 201, 296-305 (2018).</li><li>Gardenier, J. 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The authors have no conflicts of interest to disclose.

Blocking lymph flow will have broad applications in manipulating antigen delivery to the LN in healthy and diseased conditions. It is possible to use this method to control the timing of antigen delivery in order to study how continuous lymph flow regulates immune response in draining LNs. This method of lymph flow interruption can also be used to study how lymph impacts cell compartmentalization, cell activation, cell migration, and cell-cell interactions in the LN.
Mice specifically expressing human diphtheria toxin receptor (DTR) in their lymphatic endothelial cells (Flt4-cre-dtr) have been developed; these can be used to specifically deplete lymphatic vessels to study lymphatic function22. Administration of DT kills lymphatic endothelial cells along the lymphatic vessels and in the LN. The depletion of lymphatic endothelial cells can completely abrogate lymph flow regionally or systemically to study lymphatic function. This method causes significant fluid accumulation in tissue and serves as a great model to study lymphedema and lymphatic function.
Compared to the lymphatic endothelial cell-specific DTR expression model, the advantage of the lymphatic suture method is that it interrupts lymph flow with minimal damage to lymphatic endothelial cells or any other lymphatic vessel around the area. The intervention does not directly impact cells in the draining LN, so the resulting impact on the LN microenvironment or immune cell communication is a consequence of the lymph flow blockade rather than potential cell death induced by DT. Another benefit of this method is that lymph flow is instantly blocked after the surgery, so the timing of the lymph flow blockade can be better controlled.
The limitation of this method is that it can only be used to study regional intervention of lymph flow in afferent lymphatic vessels from the footpad to the pLN. This method needs identification of the exact location of the collecting lymphatic vessels. Collecting lymphatic vessels are difficult to identify in some anatomical locations, and thus this technique requires extensive anatomical and surgical training before successful identification of afferent lymphatic vessels to block lymph flow. Another limitation is that this method cannot directly block lymph entering the initial lymphatic vessels. After the suture, the blocked lymph flow may increase the interstitial fluid pressure and change the lymph flow direction in the initial lymphatic vessels. Thus, the intact lymphatic vessels around the area may compensate for the function of the interrupted lymphatic vessels and change the direction of lymph flow.
Moreover, the injection of Evans Blue dye increases the interstitial fluid pressure, which may interfere with the subsequent tracer or antigen injection. The autofluorescence of Evans Blue dye may interfere with other fluorescent tracers or other fluorophores used for immunofluorescent staining. To avoid any interaction between Evans Blue dye and potential antigens, other tracers, or potential molecular mechanisms of lymphatic function regulation, it is possible to identify the collecting lymphatic vessels without Evans Blue dye with the naked eye. This can be achieved with extensive training to identify the vessels. Other dyes, such as isosulfan blue dye can also be used to replace the Evans Blue dye.

The spatial organization of the lymphatic system provides structural and functional support to efficiently remove extracellular fluid and transport antigens and antigen-presenting cells (APCs) to the draining LNs. The initial lymphatic vessels (also named lymphatic capillaries) are highly permeable due to their discontinuous intercellular junctions, which facilitate the effective collection of fluids, cells, and other materials from surrounding extracellular spaces1. The initial lymphatic vessels merge into collecting lymphatic vessels, which have tight intercellular junctions, a continuous basement membrane, and lymphatic muscle coverage. Collecting lymphatic vessels are responsible for transporting collected lymph to the draining LNs and eventually returning lymph to the circulation2,3. The collecting lymphatic vessels that propel lymph into the draining LN are the afferent lymphatic vessels4,5,6,7. Obstruction of afferent lymphatic vessels can block lymph flow into the LNs, which is a useful technique when studying the function of lymph flow.
Previous studies have shown that lymph flow plays a significant role in transporting antigens and APCs, as well as maintaining LN homeostasis. It is well understood that tissue-derived APCs, typically activated migrating dendritic cells (DCs), travel through the afferent lymphatic vessels to the LN to activate T cells8. The idea that free-form antigens, such as microbes or soluble antigens, passively flow with lymph to the LN to activate LN-resident APCs has been gaining acceptance in the past decade9,10,11,12. Free-form antigens traveling with lymph take minutes after the infection to travel to the LN, and the LN-resident cell activation may occur within 20 min after the stimulation. This is much faster than the activation of migrating DCs, which takes more than 8 h to enter the draining LN9. Besides transporting antigens to initiate immune protection, lymph also carries cytokines and DCs to the LN to maintain its microenvironment, and to support immune cell homeostasis13,14. Previously, blocking lymph flow by suturing the afferent lymphatic vessels demonstrated that lymph is required to maintain the HEV phenotype required for supporting homeostatic T cell and B cell homing to the LN15,16,17. CCL21 is a critical chemokine that directs DC and T cell positioning in the LN8,18. Blocking lymph flow interrupts CCL21 expression in the LN and potentially interrupts DC and T cell positioning and/or interaction in the LN19. Thus, blocking lymph flow can directly or indirectly abrogate antigen/DC access to the draining LN by disrupting the LN microenvironment that regulates immune responses in the LN. To better investigate the function of lymph flow, an experimental protocol is presented (Figure 1) to block lymph flow in mice by suturing the afferent lymphatic vessels from the footpad to the pLN. This method can be an important technique for future studies on lymphatic function in healthy and diseased conditions.

<table>
	<tbody>
		<tr>
			<td>0.9% Sodium Chloride Saline</td>
			<td>Baxter</td>
			<td>JB1323</td>
			<td></td>
		</tr>
		<tr>
			<td>100% ethanol</td>
			<td>Greenfield Global</td>
			<td></td>
			<td>University of Calgary distribution services UN1170.</td>
		</tr>
		<tr>
			<td>Depilatory cream</td>
			<td>Nair</td>
			<td></td>
			<td>Nair Sensitive Formula Hair Removal Cr&#232;me with Sweet Almond Oil and Baby Oil, 200-ml. Or similar product.</td>
		</tr>
		<tr>
			<td>Evans Blue dye</td>
			<td>Sigma Life Science</td>
			<td>E2129-10G</td>
			<td>For 1 ml of Evans blue dye, add 0.1g Evans blue to 10 ml PBS. The Evens Blue solution will be filtered through 0.22 mm filters and kept sterile in 1ml aliquots.</td>
		</tr>
		<tr>
			<td>Fluorescein isothiocyanate isomer I (FITC)</td>
			<td>Sigma Life Science</td>
			<td>F7250-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps Dumont #3</td>
			<td>WPI</td>
			<td>500337</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps Dumont #5</td>
			<td>WPI</td>
			<td>500233</td>
			<td></td>
		</tr>
		<tr>
			<td>Injection apparatus</td>
			<td></td>
			<td></td>
			<td>Connect one end of polyethylene tubing to 30G &#215; &#189; needle. Attach a 1ml TB syringe to the needle. Dislodge needle shaft from another 30G &#215; &#189; needle. Insert the blunt end of the 30G &#215; &#189; needle shaft into the other end of the tubing. The inside diameter of this tubing is 0.28mm. Thus, 1.6 cm of fluid in the tubing is 1 &#956;l.</td>
		</tr>
		<tr>
			<td>Insulin syringe</td>
			<td>Becton Dickinson and Company (BD)</td>
			<td>329461</td>
			<td></td>
		</tr>
		<tr>
			<td>IRIS Forcep straight</td>
			<td>WPI</td>
			<td>15914</td>
			<td></td>
		</tr>
		<tr>
			<td>IRIS scissors</td>
			<td>WPI</td>
			<td>14218-G</td>
			<td></td>
		</tr>
		<tr>
			<td>Ketamine</td>
			<td>Narketan</td>
			<td>DIN 02374994</td>
			<td>The suppliers of Ketamine and Xylazine are usually under institutional and governmental regulation.</td>
		</tr>
		<tr>
			<td>Needles (26Gx3/8)</td>
			<td>Becton Dickinson and Company (BD)</td>
			<td>305110</td>
			<td></td>
		</tr>
		<tr>
			<td>Needles (30Gx1/2)</td>
			<td>Becton Dickinson and Company (BD)</td>
			<td>305106</td>
			<td></td>
		</tr>
		<tr>
			<td>Paton Needle Holder</td>
			<td>ROBOZ</td>
			<td>RS6403</td>
			<td>Straight, Without Lock; Serrated</td>
		</tr>
		<tr>
			<td>Phosphate-Buffered Saline (PBS)</td>
			<td>Sigma Life Science</td>
			<td>P4417-100TAB</td>
			<td></td>
		</tr>
		<tr>
			<td>Polyethylene tubing</td>
			<td>Becton Dickinson and Company (BD)</td>
			<td>427401</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical tape (1.25cmx9.1m )</td>
			<td>Transpore</td>
			<td>1527-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical tape (2.5cmx9.1m )</td>
			<td>Transpore</td>
			<td>1527-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Suture</td>
			<td>Davis and Geck CYANAMID Canada</td>
			<td>11/04</td>
			<td>0.7 metric monofilament polypropylene</td>
		</tr>
		<tr>
			<td>Syringe (1ml)</td>
			<td>Becton Dickinson and Company (BD)</td>
			<td>309659</td>
			<td></td>
		</tr>
		<tr>
			<td>VANNAS scissors</td>
			<td>World Precision Instruments (WPI)</td>
			<td>14122-G</td>
			<td></td>
		</tr>
		<tr>
			<td>Xylazine</td>
			<td>Rompun</td>
			<td>DIN02169606</td>
			<td>The suppliers of Ketamine and Xylazine are usually under institutional and governmental regulation.</td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dissecting microscope</td>
			<td>Olympus</td>
			<td></td>
			<td>Olympus S261 (522-STS OH141791) with light source: Olympus Highlight 3100</td>
		</tr>
		<tr>
			<td>Confocal microscope</td>
			<td>Leica</td>
			<td></td>
			<td>SP8</td>
		</tr>
	</tbody>
</table>

blocking lymph flow by suturing afferent lymphatic vessels in mice

Lymphatic vessels are critical in maintaining tissue fluid balance and optimizing immune protection by transporting antigens, cytokines, and cells to draining lymph nodes (LNs). Interruption of lymph flow is an important method when studying the function of lymphatic vessels. The afferent lymphatic vessels from the murine footpad to the popliteal lymph nodes (pLNs) are well-defined as the only routes for lymph drainage into the pLNs. Suturing these afferent lymphatic vessels can selectively prevent lymph flow to the pLNs. This method allows for interference in lymph flow with minimal damage to the lymphatic endothelial cells in the draining pLN, the afferent lymphatic vessels, as well as other lymphatic vessels around the area. This method has been used to study how lymph impacts high endothelial venules (HEV) and chemokine expression in the LN, and how lymph flows through the adipose tissue surrounding the LN in the absence of functional lymphatic vessels. With the growing recognition of the importance of lymphatic function, this method will have broader applications to further unravel the function of lymphatic vessels in regulating the LN microenvironment and immune responses.

Lymphatic vessel suture has been used in previous studies15,16,17,19, where it served as an important tool to study the function of lymph flow before the molecular biology of lymphatic vessels was better understood. Blocking lymph flow interrupts LN homeostasis, which leads to HEVs losing the critical gene expression needed for optimal lymphocyte homing to the LN15,16,17. Since then, it took another two decades to demonstrate that DCs traveling with lymph are crucial in maintaining the HEV gene expression profile and lymphocytes homing to the LN13. The shear stress provided by the lymph flow is critical to stimulate chemokine expression in the LN. Blocking lymph flow interrupts chemokine CCL21 expression in the LN19, which is critical in directing DC and T cell positioning in the LN. Therefore, interrupted flow may compromise DCs and T cells positioning in the LN8,18.
Immediately after the surgery, a small molecular weight fluorescent tracer, FITC, was used to track lymph flow. FITC (10 &#181;L of 2% FITC) was injected intradermally in the footpad of the sham control and the lymphatic sutured leg. The draining pLNs were collected 2, 6, and 12 h later. The draining pLNs were embedded in OCT, and 20 &#181;m frozen sections were prepared. Confocal images showed substantially reduced FITC accumulation in the pLNs after suture. The residual FITC in the pLNs was preferentially accumulated in the LN sinuses (Figure 2).
How the lymph flows through the adipose tissue surrounding the LN was investigated using lymphatic suture. The afferent lymphatic vessels leading to the pLNs were sutured to block lymph flow, and it was determined that the perinodal adipose tissue could support a small amount of lymph flow when lymphatic vessels were blocked21. The lymph flow through the adipose tissue to the capsule of the LN was mapped; it appeared to feed into the LN sinuses. Small amounts of lymph may have flowed into the LN sinuses over time (Figure 3).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61178/61178fig01.jpg" /> 
Figure 1: Steps of popliteal LN (pLN) afferent lymphatic vessel suture.&#160;Briefly, after mice were anesthetized with a ketamine and xylazine mixture, their legs were shaved, and the residual fur was removed by a depilatory cream. The right leg was used for suture and the left leg was the sham control. The right side of the footpad was intradermally injected with 5 &#181;L of 1% Evans Blue dye prepared in PBS. (A) By gently massaging the footpad, Evans Blue dye filled the afferent lymphatic vessels. (B) A small skin cut was performed 5 mm away from the pLN to expose the lymphatic vessels, which are indicated by the two white arrows. (C,D) Both afferent lymphatic vessels were sutured. (E) The skin excision was closed by sutures. (F) The control leg received Evans blue injection, skin excision, and suture closure without suturing the lymphatic vessels. (G) The success of the lymph flow blockage was indicated by Evans blue dye, which entered the pLN of the control leg but not the sutured leg. (H,I) The collected pLNs were embedded in OCT compound with subcapsular sinus (SCS) and medullary sinus (MS) facing the side of the cryomold before snap freezing in liquid nitrogen. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61178/61178fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61178/61178fig02.jpg" /> 
Figure 2: FITC distribution in the draining pLNs of the sham or sutured leg.&#160;Confocal images of pLNs collected 2, 6, and 12 h after FITC injection showed substantially reduced FITC accumulation in the pLNs after suture. The residual FITC in the pLNs was preferentially found in the LN sinuses. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61178/61178fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61178/61178fig03.jpg" /> 
Figure 3: FITC distribution in the perinodal adipose tissue (PAT), around the draining pLNs of the sham or sutured leg.&#160;Confocal images of the PAT and the LN showed that FITC enters the PAT and the LN sinuses but was not effectively distributed throughout the LN when lymphatic vessels were blocked. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61178/61178fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Blocking Lymph Flow by Suturing Afferent Lymphatic Vessels in Mice at JoVE.com

Blocking Lymph Flow by Suturing Afferent Lymphatic Vessels in Mice

A protocol to block lymph flow by surgical suturing of afferent lymphatic vessels is presented.

Lymphatic vessels are critical in maintaining tissue fluid balance and optimizing immune protection by transporting antigens, cytokines, and cells to ...

blocking-lymph-flow-by-suturing-afferent-lymphatic-vessels-in-mice

Nanyang Technological University

Research

JoVE Journal

Immunology and Infection

5.4K Views.  Harbin Medical University. A protocol to block lymph flow by surgical suturing of afferent lymphatic vessels is presented.

Video: Blocking Lymph Flow by Suturing Afferent Lymphatic Vessels in Mice

Non-surgical Intratracheal Instillation of Mice with Analysis of Lungs and Lung Draining Lymph Nodes by Flow Cytometry

Phagocytic cells such as alveolar macrophages and lung dendritic cells (LDCs) continuously sample antigens from the alveolar spaces in the 
lungs. LDCs, in particular, are known to migrate to the lung draining lymph nodes (LDLNs) where they present inhaled antigens to T cells initiating an 
appropriate immune response to a variety of immunogens1,2. To model interactions between the lungs and airborne antigens in mice, antigens can be 
administered intranasally1,3,4, intratracheally5 or as aerosols6. Delivery by each route involves distinct technical skills and limitations that need to be 
considered before designing an experiment. For example, intranasal and aerosolized exposure delivers antigens to both the lungs and the upper respiratory 
tract. Hence antigens can access the nasal associated lymphoid tissue (NALT)7, potentially complicating interpretation of the results. In addition, swallowing, 
sneezing and the breathing rate of the mouse may also lead to inconsistencies in the doses delivered. Although the involvement of the upper respiratory tract may 
be preferred for some studies, it can complicate experiments focusing on events specifically initiated in the lungs. In this setting, the intratracheal (i.t) 
route is preferable as it delivers test materials directly into the lungs and bypasses the NALT. Many i.t injection protocols involve either blind intubation of the 
trachea through the oral cavity or surgical exposure of the trachea to access the lungs. Herein, we describe a simple, consistent, non-surgical method for i.t 
instillation. The opening of the trachea is visualized using a laryngoscope and a bent gavage needle is then inserted directly into the trachea to deliver the 
innoculum. We also describe procedures for harvesting and processing of LDLNs and lungs for analysis of antigen trafficking by flow cytometry.

We illustrate non-surgical delivery of test materials into the lungs of anesthetized mice via the trachea. This method permits lung exposure to bacterial and viral pathogens, cytokines, antibodies, beads, chemicals, or dyes. We further describe harvesting and processing of lungs and lung draining lymph nodes (LDLNs) for flow cytometry.

Phagocytic cells such as alveolar macrophages and lung dendritic cells (LDCs) continuously sample antigens from the alveolar spaces in the 
lungs. LDCs, ...

Introducing Shear Stress in the Study of Bacterial Adhesion

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the initial and determining step of the pathogenesis. Although experimentally adhesion is mostly studied in static conditions adhesion actually takes place in the presence of flowing liquid. First encounters between bacteria and their host often occur at the mucosal level, mouth, lung, gut, eye, etc. where mucus flows along the surface of epithelial cells. Later in infection, pathogens occasionally access the blood circulation causing life-threatening illnesses such as septicemia, sepsis and meningitis. A defining feature of these infections is the ability of these pathogens to interact with endothelial cells in presence of circulating blood. The presence of flowing liquid, mucus or blood for instance, determines adhesion because it generates a mechanical force on the pathogen. To characterize the effect of flowing liquid one usually refers to the notion of shear stress, which is the tangential force exerted per unit area by a fluid moving near a stationary wall, expressed in dynes/cm2. Intensities of shear stress vary widely according to the different vessels type, size, organ, location etc. (0-100 dynes/cm2). Circulation in capillaries can reach very low shear stress values and even temporarily stop during periods ranging between a few seconds to several minutes 1. On the other end of the spectrum shear stress in arterioles can reach 100 dynes/cm2 2. The impact of shear stress on different biological processes has been clearly demonstrated as for instance during the interaction of leukocytes with the endothelium 3. To take into account this mechanical parameter in the process of bacterial adhesion we took advantage of an experimental procedure based on the use of a disposable flow chamber 4. Host cells are grown in the flow chamber and fluorescent bacteria are introduced in the flow controlled by a syringe pump. We initially focused our investigations on the bacterial pathogen Neisseria meningitidis, a Gram-negative bacterium responsible for septicemia and meningitis. The procedure described here allowed us to study the impact of shear stress on the ability of the bacteria to: adhere to cells 1, to proliferate on the cell surface 5and to detach to colonize new sites 6 (Figure 1). Complementary technical information can be found in reference 7. Shear stress values presented here were chosen based on our previous experience1 and to represent values found in the literature. The protocol should be applicable to a wide range of pathogens with specific adjustments depending on the objectives of the study.

During the infection process, a key step is the adhesion of pathogens with host cells. In most instances this adhesion step occurs in the presence of mechanical stress generated by flowing liquid. We describe a technique that introduces shear stress as an important parameter in the study of bacterial adhesion.

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the ...

The Mesenteric Lymph Duct Cannulated Rat Model: Application to the Assessment of Intestinal Lymphatic Drug Transport

The intestinal lymphatic system plays key roles in fluid transport, lipid absorption and immune function. Lymph flows directly from the small intestine via a series of lymphatic vessels and nodes that converge at the superior mesenteric lymph duct. Cannulation of the mesenteric lymph duct thus enables the collection of mesenteric lymph flowing from the intestine. Mesenteric lymph consists of a cellular fraction of immune cells (99% lymphocytes), aqueous fraction (fluid, peptides and proteins such as cytokines and gut hormones) and lipoprotein fraction (lipids, lipophilic molecules and apo-proteins). The mesenteric lymph duct cannulation model can therefore be used to measure the concentration and rate of transport of a range of factors from the intestine via the lymphatic system. Changes to these factors in response to different challenges (e.g., diets, antigens, drugs) and in disease (e.g., inflammatory bowel disease, HIV, diabetes) can also be determined. An area of expanding interest is the role of lymphatic transport in the absorption of orally administered lipophilic drugs and prodrugs that associate with intestinal lipid absorption pathways. Here we describe, in detail, a mesenteric lymph duct cannulated rat model which enables evaluation of the rate and extent of lipid and drug transport via the lymphatic system for several hours following intestinal delivery. The method is easily adaptable to the measurement of other parameters in lymph. We provide detailed descriptions of the difficulties that may be encountered when establishing this complex surgical method, as well as representative data from failed and successful experiments to provide instruction on how to confirm experimental success and interpret the data obtained.

Here we describe a technique to cannulate the mesenteric lymph duct in rats which enables quantification of lipid and drug transport via the lymphatic system following intestinal delivery. The technique can be adapted to assess mesenteric lymph concentrations and/or transport of fluid, immune cells, peptides, proteins and lipophilic molecules.

The intestinal lymphatic system plays key roles in fluid transport, lipid absorption and immune function. Lymph flows directly from the small intestine ...

Vasodilation of Isolated Vessels and the Isolation of the Extracellular Matrix of Tight-skin Mice

The interferon regulatory factor 5 (IRF5) is crucial for cells to determine if they respond in a pro-inflammatory or anti-inflammatory fashion. IRF5's ability to switch cells from one pathway to another is highly attractive as a therapeutic target. We designed a decoy peptide IRF5D with a molecular modeling software for designing small molecules and peptides.
IRF5D inhibited IRF5, reduced alterations in extracellular matrix, and improved endothelial vasodilation in the tight-skin mouse (Tsk/+). The Kd of IRF5D for recombinant IRF5 is 3.72 &plusmn; 0.74 x 10-6 M as determined by binding experiments using biolayer interferometry experiments. Endothelial cells (EC) proliferation and apoptosis were unchanged using increasing concentrations of IRF5D (0 to 100 &#181;g/mL, 24 h). Tsk/+ mice were treated with IRF5D (1 mg/kg/d subcutaneously, 21 d). IRF5 and ICAM expressions were decreased after IRF5D treatment. Endothelial function was improved as assessed by vasodilation of facialis arteries from Tsk/+ mice treated with IRF5D compared to Tsk/+ mice without IRF5D treatment. As a transcription factor, IRF5 traffics from the cytosol to the nucleus. Translocation was assessed by immunohistochemistry on cardiac myocytes cultured on the different cardiac extracellular matrices. IRF5D treatment of the Tsk/+ mouse resulted in a reduced number of IRF5 positive nuclei in comparison to the animals without IRF5D treatment (50 &#181;g/mL, 24 h). These findings demonstrate the important role that IRF5 plays in inflammation and fibrosis in Tsk/+ mice.

We describe the isolation of cardiac extracellular matrix from C57Bl/6J control mice, tight-skin mice, and tight-skin mice treated with the IRF5 inhibitory peptide. We also describe the vasodilation studies on the isolated vessels from C57Bl/6J, tight-skin mice and tight-skin mice treated with the IRF5 inhibitory peptide.

The interferon regulatory factor 5 (IRF5) is crucial for cells to determine if they respond in a pro-inflammatory or anti-inflammatory fashion. IRF5's ...

Intracellular Staining and Flow Cytometry to Identify Lymphocyte Subsets within Murine Aorta, Kidney and Lymph Nodes in a Model of Hypertension

It is now well known that T lymphocytes play a critical role in the development of several cardiovascular diseases1,2,3,4,5. For example, studies from our group have shown that hypertension is associated with an excessive accumulation of T cells in the vessels and kidney during the development of experimental hypertension6. Once in these tissues, T cells produce several cytokines that affect both vascular and renal function leading to vasoconstriction and sodium and water retention1,2. To fully understand how T cells cause cardiovascular and renal diseases, it is important to be able to identify and quantify the specific T cell subsets present in these tissues. T cell subsets are defined by a combination of surface markers, the cytokines they secrete, and the transcription factors they express. The complexity of the T cell population makes flow cytometry and intracellular staining an invaluable technique to dissect the phenotypes of the lymphocytes present in tissues. Here, we provide a detailed protocol to identify the surface and intracellular markers (cytokines and transcription factors) in T cells isolated from murine kidney, aorta and aortic draining lymph nodes in a model of angiotensin II induced hypertension. The following steps are described in detail: isolation of the tissues, generation of the single cell suspensions, ex vivo stimulation, fixation, permeabilization and staining. In addition, several fundamental principles of flow cytometric analyses including choosing the proper controls and appropriate gating strategies are discussed.

This article provides detailed methodology to identify and quantify functional T lymphocyte subsets present within murine kidney, aorta and lymph nodes by intracellular staining and flow cytometry. The model of angiotensin II induced hypertension was chosen to explain, step-by-step, the procedures and fundamental principles of flow cytometry and intracellular staining.

It is now well known that T lymphocytes play a critical role in the development of several cardiovascular diseases1,2,3,4,5. For example, studies from our ...

Isolation and In Vitro Culture of Murine and Human Alveolar Macrophages

Alveolar macrophages are terminally differentiated, lung-resident macrophages of prenatal origin. Alveolar macrophages are unique in their long life and their important role in lung development and function, as well as their lung-localized responses to infection and inflammation. To date, no unified method for identification, isolation, and handling of alveolar macrophages from humans and mice exists. Such a method is needed for studies on these important innate immune cells in various experimental settings. The method described here, which can be easily adopted by any laboratory, is a simplified approach to harvesting alveolar macrophages from bronchoalveolar lavage fluid or from lung tissue and maintaining them in vitro. Because alveolar macrophages primarily occur as adherent cells in the alveoli, the focus of this method is on dislodging them prior to harvest and identification. The lung is a highly vascularized organ, and various cell types of myeloid and lymphoid origin inhabit, interact, and are influenced by the lung microenvironment. By using the set of surface markers described here, researchers can easily and unambiguously distinguish alveolar macrophages from other leukocytes, and purify them for downstream applications. The culture method developed herein supports both human and mouse alveolar macrophages for in vitro growth, and is compatible with cellular and molecular studies.

Isolation and In Vitro Culture of Murine and Human Alveolar Macrophages

This communication describes methodologies for isolation and culture of alveolar macrophages from humans and murine models for experimental purposes.

Alveolar macrophages are terminally differentiated, lung-resident macrophages of prenatal origin. Alveolar macrophages are unique in their long life and ...

Deep Vein Thrombosis Induced by Stasis in Mice Monitored by High Frequency Ultrasonography

Venous thrombosis is a common condition affecting 1 - 2% of the population, with an annual incidence of 1 in 500. Venous thrombosis can lead to death through pulmonary embolism or results in the post-thrombotic syndrome, characterized by chronic leg pain, swelling, and ulceration, or in chronic pulmonary hypertension resulting in significant chronic respiratory compromise. This is the most common cardiovascular disease after myocardial infarction and ischemic stroke and is a clinical challenge for all medical disciplines, as it can complicate the course of other disorders such as cancer, systemic disease, surgery, and major trauma.
Experimental models are necessary to study these mechanisms. The stasis model induces consistent thrombus size and a quantifiable amount of thrombus. However, it is necessary to systematically ligate side branches of the inferior vena cava to avoid variability in thrombus sizes and any erroneous data interpretation. We have developed a non-invasive technique to measure thrombus size using ultrasonography. Using this technique, we can assess thrombus development and resolution over time in the same animal. This approach limits the number of mice required for quantification of venous thrombosis consistent with the principle of replacement, reduction, and refinement of animals in research. We have demonstrated that thrombus weight and histological analysis of thrombus size correlate with measurement obtained with ultrasonography. Therefore, the current study describes how to induce deep vein thrombosis in mice using the inferior vena cava stasis model and how to monitor it using high frequency ultrasound.

The present protocol describes the steps to obtain venous thrombosis using a stasis model. In addition, we are using a non-invasive method to measure thrombus formation and resolution over time.

Venous thrombosis is a common condition affecting 1 - 2% of the population, with an annual incidence of 1 in 500. Venous thrombosis can lead to death ...

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.

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 ...

Determination of Regulatory T Cell Subsets in Murine Thymus, Pancreatic Draining Lymph Node and Spleen Using Flow Cytometry

Our immune system consists of a number and variety of immune cells including regulatory T cells (Treg) cells. Treg cells can be divided into two subsets, thymic derived Treg (tTreg) cells and peripherally induced Treg (pTreg) cells. They are present in different organs of our body and can be distinguished by specific markers, such as Helios and Neuropilin 1. It has been reported that tTreg cells are functionally more suppressive than pTreg cells. Therefore, it is important to determine the proportion of both tTreg and pTreg cells when investigating heterogeneous cell populations. Herein, we collected thymic glands, pancreatic draining lymph nodes and spleens from normoglycemic non-obese diabetic mice to distinguish tTreg cells from pTreg cells using flow cytometry. We manually prepared single cell suspensions from these organs. Fluorochrome conjugated surface CD4, CD8, CD25, and Neuropilin 1 antibodies were used to stain the cells. They were kept in the fridge overnight. On the next day, the cells were stained with fluorochrome conjugated intracellular Foxp3 and Helios antibodies. These markers were used to characterize the two subsets of Treg cells. This protocol demonstrates a simple but practical way to prepare single cells from murine thymus, pancreatic draining lymph node and spleen and use them for subsequent flow cytometric analysis.

Herein, we present a protocol to prepare single cells from murine thymus, pancreatic draining lymph node and spleen to further study these cells using flow cytometry. In addition, this protocol was used for determining the subsets of regulatory T cells using flow cytometry.

Our immune system consists of a number and variety of immune cells including regulatory T cells (Treg) cells. Treg cells can be divided into two subsets, ...

Co-staining Blood Vessels and Nerve Fibers in Adipose Tissue

Recent studies have highlighted the critical role of angiogenesis and sympathetic innervation in adipose tissue remodeling during the development of obesity. Therefore, developing an easy and efficient method to document the dynamic changes in adipose tissue is necessary. Here, we describe a modified immunofluorescent approach that efficiently co-stains blood vessels and nerve fibers in adipose tissues. Compared to traditional and recently developed methods, our approach is relatively easy to follow and more efficient in labeling the blood vessels and nerve fibers with higher densities and less background. Moreover, the higher resolution of the images further allows us to accurately measure the area of the vessels, amount of branching, and length of the fibers by open source software. As a demonstration using our method, we show that brown adipose tissue (BAT) contains higher amounts of blood vessels and nerve fibers compared to white adipose tissue (WAT). We further find that among the WATs, subcutaneous WAT (sWAT) has more blood vessels and nerve fibers compared to epididymal WAT (eWAT). Our method thus provides a useful tool for investigating adipose tissue remodeling.

New blood vessel formation and sympathetic innervation play pivotal roles in adipose tissue remodeling. However, there remain technical issues in visualizing and quantitatively measuring adipose tissue. Here we present a protocol to successfully label and quantitatively compare the densities of blood vessels and nerve fibers in different adipose tissues.

Recent studies have highlighted the critical role of angiogenesis and sympathetic innervation in adipose tissue remodeling during the development of ...