This work was supported by the NIH (R01 AI43458 to H.L.W.).

The protocol was approved by the Standing Committee on Animals at Harvard Medical School and Brigham and Women&#8217;s Hospital, protocol 2016N000230.
1. Mice used for the experiment
<ol>
	<li>Use 8-week old male and female mice on the B6 background for administering the antibody mix.</li>
	<li>Use CX3CR1GFP/WTCCR2RFP/WT mice to determine whether ex vivo whole LN imaging can also be applied to reporter mice without administering antibody mix as well as to investigate th...

<ol>
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Y., Casey, K. A., Kastenmuller, W., Germain, R. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dendritic+cell+and+antigen+dispersal+landscapes+regulate+T+cell+immunity.">Dendritic cell and antigen dispersal landscapes regulate T cell immunity.</a> The Journal of Experimental Medicine. 214, 3105-3122 (2017).</li><li>Hauser, A. 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=Definition+of+germinal-center+B+cell+migration+in+vivo+reveals+predominant+intrazonal+circulation+patterns.">Definition of germinal-center B cell migration in vivo reveals predominant intrazonal circulation patterns.</a> Immunity. 26, 655-667 (2007).</li><li>Allen, C. D., Okada, T., Tang, H. L., Cyster, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+of+germinal+center+selection+events+during+affinity+maturation.">Imaging of germinal center selection events during affinity maturation.</a> Science. 315, 528-531 (2007).</li><li>Arnon, T. I., Horton, R. M., Grigorova, I. L., Cyster, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualization+of+splenic+marginal+zone+B-cell+shuttling+and+follicular+B-cell+egress.">Visualization of splenic marginal zone B-cell shuttling and follicular B-cell egress.</a> Nature. 493, 684-688 (2013).</li><li>Sipkins, D. 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G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cannabinoid+receptor+2+mediates+the+retention+of+immature+B+cells+in+bone+marrow+sinusoids.">Cannabinoid receptor 2 mediates the retention of immature B cells in bone marrow sinusoids.</a> Nature Immunology. 10, 403-411 (2009).</li><li>Nakagaki, B. 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=Immune+and+metabolic+shifts+during+neonatal+development+reprogram+liver+identity+and+function.">Immune and metabolic shifts during neonatal development reprogram liver identity and function.</a> Journal of Hepatology. (6), 1294-1307 (2018).</li><li>Wang, H., La Russa, M., Qi, L. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CRISPR/Cas9+in+Genome+Editing+and+Beyond.">CRISPR/Cas9 in Genome Editing and Beyond.</a> Annual Review of Biochemistry. 85, 227-264 (2016).</li><li>Roozendaal, 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=Conduits+mediate+transport+of+low-molecular-weight+antigen+to+lymph+node+follicles.">Conduits mediate transport of low-molecular-weight antigen to lymph node follicles.</a> Immunity. 30, 264-276 (2009).</li><li>Sarder, P., 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=All-near-infrared+multiphoton+microscopy+interrogates+intact+tissues+at+deeper+imaging+depths+than+conventional+single-+and+two-photon+near-infrared+excitation+microscopes.">All-near-infrared multiphoton microscopy interrogates intact tissues at deeper imaging depths than conventional single- and two-photon near-infrared excitation microscopes.</a> Journal of Biomedical Optics. 18, 106012 (2013).</li></ol>

The authors have nothing to disclose.

The combination of imaging with other techniques, including molecular biology and high dimensional immunophenotyping has enhanced our ability to investigate immune cells in their native context. In fact, while other approaches may require tissue digestion and cell isolation &#8211; which can lead to loss of tissue integrity - the use of in vivo or ex vivo imaging grants a great advantage in investigating different cell subtypes in a geographical fashion3,16. It i...

Lymph nodes (LNs) are ovoid-shaped organs widely present throughout the body with the crucial function of bridging the innate and adaptive immune responses. LNs filter the lymph in order to identify foreign particles and cancerous cells to mount an immune response against them1. Antigen presenting cells (APCs), T cells and B cells work alongside to generate antigen-specific antibodies (humoral immunity) and cytotoxic lymphocytes (cellular immunity) to eliminate the foreign particles and cancerous cells2. Thus, understanding the dynamics of the immune cells present in the lymphatic system will have important implications for the vaccine development and cancer immunotherapy.
The advent of powerful microscopes - including new confocal and super resolution microscopes - has allowed an extraordinary advancement in understanding how different immune cell populations behave in their native environment3. It is now possible to image several simultaneous cell subtypes using a combination of probes with genetically modified mice that express fluorescent proteins under control of specific targets4,5. In fact, high dimensional techniques, including mass cytometry and multi-parametric flow analysis have been crucial to expanding our knowledge on different immune cell compartmentalization and functionality in the health and disease6,7. However, to prepare samples for these techniques, tissues need digestion and cells are separated from their natural milieu to be analyzed in cell suspensions. To surpass these limitations and allow a better translation in biology, the goal of the protocol proposed here is to apply a straightforward methodology to image ex vivo whole lymph nodes using stock confocal microscopes with the benefit of improved speed, tissue structure preservation, and cell viability compared to the conventional immunofluorescence staining. By using this approach, we were able to show that mice deficient for &#947;&#948; T cells, a subtype of T lymphocyte involved in host early defense against pathogens4, have compromised follicles and T cell zones as compared to wild type mice. These findings allowed us to pursue a study in which we demonstrated that &#947;&#948; T cells play a critical role in the homeostasis of lymphoid organs and humoral immune response4. Furthermore, this protocol provides a physiologic pathway for probes and antibodies to reach the lymph node, as they are administered subcutaneously and dissipate through the tissue lymphatic circulation, building on previous reports that used in situ labeling with antibodies to visualize lymphatic-associated structures8,9, germinal center dynamics10,11,12, and targets readily accessible to blood flow13,14,15.

<table>
	<tbody>
		<tr>
			<td>BV421 anti-CD4</td>
			<td>BD Horizon</td>
			<td>562891</td>
			<td>GK1.5; 0.2 mg mL-1</td>
		</tr>
		<tr>
			<td>BB515 anti-CD19</td>
			<td>BD Horizon</td>
			<td>564509</td>
			<td>1D3; 0.2 mg mL-1</td>
		</tr>
		<tr>
			<td>BB515 Rat IgG2a, &#954; Isotype Control</td>
			<td>BD Horizon</td>
			<td>564418</td>
			<td>R35-95; 0.2 mg mL-1</td>
		</tr>
		<tr>
			<td>BV421 Mouse IgG2b, K Isotype Control</td>
			<td>BD Horizon</td>
			<td>562603</td>
			<td>R35-38 0.2 mg mL-1</td>
		</tr>
		<tr>
			<td>Cellview culture dish</td>
			<td>Greiner-Bio</td>
			<td>627861</td>
			<td>35x10 mm with glass bottom</td>
		</tr>
		<tr>
			<td>Insulin syringes</td>
			<td>BD Plastipak</td>
			<td>-</td>
			<td>Insulin U-100</td>
		</tr>
		<tr>
			<td>Kimwipes</td>
			<td>Kimtech Science Brand</td>
			<td>7557</td>
			<td>size 21 x 20 cm / 100 sheets per box</td>
		</tr>
		<tr>
			<td>Microsurgery curved forceps</td>
			<td>WEP Surgical Instruments</td>
			<td>custom made</td>
			<td>12.5 cm</td>
		</tr>
		<tr>
			<td>Microsurgery curved scissors</td>
			<td>WEP Surgical Instruments</td>
			<td>custom made</td>
			<td>11.5 cm</td>
		</tr>
		<tr>
			<td>Needle</td>
			<td>BD PrecisionGlide</td>
			<td>-</td>
			<td>30 gauge &#215; &#189; inch</td>
		</tr>
		<tr>
			<td>Nikon Eclipse Te + A1R confocal head</td>
			<td>Nikon</td>
			<td>-</td>
			<td>loaded with main 4 laser lines (405, 488, 543 and 647 nm)</td>
		</tr>
		<tr>
			<td>PE anti-F4/80</td>
			<td>BD Pharmigen</td>
			<td>565410</td>
			<td>T45-2342; 0.2 mg mL-1</td>
		</tr>
		<tr>
			<td>PE Rat IgG2a, &#954; Isotype Control</td>
			<td>BD Pharmigen</td>
			<td>553930</td>
			<td>R35-95; 0.2 mg mL-1</td>
		</tr>
		<tr>
			<td>Zeiss LSM 710 confocal microscope</td>
			<td>Zeiss</td>
			<td>-</td>
			<td>loaded with main 4 laser lines (405, 488, 543 and 647 nm)</td>
		</tr>
	</tbody>
</table>

visualizing lymph node structure and cellular localization using ex-vivo confocal microscopy

Lymph nodes (LNs) are organs spread within the body, where the innate immune responses can connect with the adaptive immunity. In fact, LNs are strategically interposed in the path of the lymphatic vessels, allowing intimate contact of tissue antigens with all resident immune cells in the LN. Thus, understanding the cellular composition, distribution, location and interaction using ex vivo whole LN imaging will add to the knowledge on how the body coordinates local and systemic immune responses. This protocol shows an ex vivo imaging strategy following an in vivo administration of fluorescent-labeled antibodies that allows a very reproducible and easy-to-perform methodology by using conventional confocal microscopes and stock reagents. Through subcutaneous injection of antibodies, it is possible to label different cell populations in draining LNs without affecting tissue structures that can be potentially damaged by a conventional immunofluorescence microscopy technique.

This manuscript shows techniques to remove inguinal and popliteal lymph nodes without damaging their structure following the injection of fluorescent-labeled antibodies to stain specific cell populations in these organs (Figure 1 and Figure 2).
The powerful combination of immunolabeling of LN cells with BV421 anti-CD4 and BB515 anti-CD19 and confocal imaging analysis defined the localization of T cells (CD4+) and B cells (CD19+) in in...

Watch this Scientific Journal Video about Visualizing Lymph Node Structure and Cellular Localization using Ex-Vivo Confocal Microscopy at JoVE.com

Visualizing Lymph Node Structure and Cellular Localization using Ex-Vivo Confocal Microscopy

This protocol describes a technique to image different cell populations in draining lymph nodes without alterations in the organ structure.

Lymph nodes (LNs) are organs spread within the body, where the innate immune responses can connect with the adaptive immunity. In fact, LNs are ...

This reproducible and easy to perform protocol uses an ex-vivo lymph node imaging strategy to track the draining of in-vivo administered fluorescent labeled antibodies to local secondary lymphoid organs. Demonstrating this technique allows a specific visualization of the procedure, which can facilitate a successful execution of the protocol. This is a very simple and straightforward technique that can be performed by anyone.The only challenging aspect is the mouse handling, which requires some training. This technique has the benefit of an improved speed tissue exertion preservation and cell viability compared to the conventional fluorescent staining methods. Training the procedure would be Bruna Tatematsu, a technician from the laboratory.Dilute the antibodies of interest, conjugated to the appropriate fluorophores, in 100 microliters of PBS for inguinal lymph node imaging, or 50 microliters of PBS for popliteal lymph node imaging. For inguinal lymph node imaging, load 100 microliters of the antibody cocktail into a one milliliter insulin syringe, equipped with a 30 gauge by half inch needle, and subcutaneously inject the antibodies into the inner thigh of the experimental mouse. For popliteal lymph node imaging, inject 50 microliters of the antibody cocktail subcutaneously into one paw pad of the experimental animal.Then return the animal to its home box. For inguinal draining lymph node harvest, after waiting at least three hours from the injection, immobilize the mouse on the acrylic stage with adhesive tape and apply mineral oil to the abdominal skin. Use standard microsurgery scissors and microsurgery curved forceps to make a midline skin incision in the abdomen from the pubis to the xyphoid process, and dissociate the abdominal musculature from the skin.Make horizontal skin incisions in the top and bottom of the vertical incision line, to create skin flaps on the side of injection, and retract the skin to visualize the lymph node. Secure the skin flap to the acrylic plate, and use the forceps to remove the translucent, usually bilobular spherical inguinal draining lymph node. For popliteal draining lymph node harvest, at least 12 hours after the injection, immobilize the mouse in the prone position on an acrylic stage.Apply mineral oil to the calf and knee on the injected side of the animal. Next, make a midline incision in the calf from the heel to the knee, and dissociate the calf musculature from the skin. Expose the popliteal fossa.The popliteal lymph node will appear as a translucent sphere within the fossa. Then, remove the lymph node with the microsurgery curved forceps. To prepare the lymph node for imaging, place the whole organs in a 35 by 10 millimeter culture dish with a glass bottom, and use forceps to remove any fat surrounding the tissue.Center the organ in the middle of the dish, and cover the tissue with a piece of saline-soaked delicate task wiper. For ex vivo imaging, position the dish in the inverted confocal microscope slot and use the conventional light of the confocal microscope and the 4-10X objective to obtain the correct focus. Change from the light function to the laser mode and use an isotope-stained, non-stained, or non-fluorescent sample to adjust the laser power, offset, and gain to remove the auto fluorescence and any unspecified staining.Acquire images under the 4, 10 and the 20X objectives focusing on the lymph node structure and cellular distribution and using a 1024 by 1024 pixel definition. Then, use an appropriate imaging analysis software program to separate the channels, to add the scale and colors of interest, and to reconstruct the 3D view. The powerful combination of immunolabeling of lymph node cells with anti-CD4 and anti-CD19 antibodies and confocal imaging analysis allows the localization of T and B cells within the inguinal lymph nodes.In the popliteal lymph nodes, as in the inguinal tissue, the B cell follicles are surrounded by T cell populations, a hallmark of the lymph node structure. As observed in these images, phagocytes do not internalize the injected antibodies, indicating that the B and T cell staining is specific. Moreover, re-reconstruction of the labeling indicates that the T and B cell staining do not overlap, further confirming the specificity of the staining.Monocellular cells are observed throughout the inguinal lymph node, including the subcapsular sinus. With the majority of the mononuclear cells expressing CX3XR1, followed by CCR2 and CXCR31CCR2 double positive cells. The same pattern of cell distribution and cell phenotypes is observed in the popliteal lymph node.Both lymph nodes also exhibit dark regions without mononuclear cell receptor expression that are occupied by lymphocytes. Moreover, mononuclear cells are scarce within the inner area of the lymph nodes, remaining concentrated in the outer areas of the tissue, indicating that these cells primarily occupy the lymph node subcapsular sinus. The antibody mixture needs to be precisely injected into the subcutaneous tissue for the lymphatic system to properly drain the antibodies to the lymph node.This method can be applied to the biodistribution of fluorescent labeled drugs, and to cell targeting studies of fluorescent labeled nanoparticles.

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12.8K Views.  Brigham and Women's Hospital, Harvard Medical School. This reproducible and easy to perform protocol uses an ex-vivo lymph node imaging strategy to track the draining of in-vivo administered fluorescent labeled antibodies to local secondary lymphoid organs. Demonstrating this technique allows a specific visualization of the procedure, which can facilitate a successful execution of the protocol. This is a very simple and straightforward technique that can be performed by anyone.The only challenging aspect is the mouse handling, which requi...