The authors would like to thank James Fosse for his excellent work on all videography and video processing; Michael Marti for his excellent work in the generation of digitized cattle images; Lilia Walther for her help with RNA extraction and Bioanalyzer runs; Mitch Palmer and Carly Kanipe for their helpful review and feedback on lymph node images; and the animal care and veterinary staff at the National Animal Disease Center for all of their hard work and assistance with animal husbandry and the preparation for necropsies.

The authors have no conflicts of interest to disclose. All research is funded with intramural funds from the U.S. Department of Agriculture, Agricultural Research Service. All references to specific products are provided for the purpose of experimental reproducibility and do not represent any endorsement of these products by the federal government.

The majority of transcriptomic studies and the associated protocols focus on mouse, rat, or post-mortem human samples. However, investigations in livestock and wildlife provide a wide range of opportunities for the characterization of the immune response to disease, both as applicable to veterinary medicine and, in regard to zoonotic diseases, to human public health. This protocol provided an outline of key considerations for high-integrity RNA extraction from tissues from large animals, such as cattle, bison, goats, and sheep. The size of the animals, as well as the conditions for the sample collection, make the recovery a more extensive process, with a longer post-mortem processing time than for mouse lymph node recovery. Similarly, the large size of these lymph nodes necessitates protocols that recover parallel samples from different animals as well as samples that are representative of the immunological/pathological changes within the lymph node. The suggestions for sample collection in this protocol provide for the recovery of intact RNA as well as for representative profiles based on the sectioning of the lymph node.
As a demonstration of the importance of a standardized sampling strategy and protocol, as presented here, we surveyed 25 papers from the PubMed Central database that characterized the transcriptomes of livestock lymph nodes. One paper indicated the processing of a large lymph node section at one time, one discussed specific laser capture microdissection methods, one mentioned that a &#34;representative sample&#34; was collected from the lymph node, and only one paper46&#160;indicated that the piece of lymph node collected (10 mm3&#160;in size) included both cortex and medulla regions. While other papers noted that small samples (generally 30 - 100 mg) were processed for RNA analysis, 84% of the papers did not mention a sampling strategy for the collection of these tissue pieces. As RNA-sequencing is still relatively expensive, the analysis of multiple sections per lymph node is unlikely to be financially viable in most cases, especially since biological replicate samples are typically prioritized for statistical analysis. By collecting a sample across a wedge of a sagittally sectioned lymph node, RNA from lymph node regions rich in different types of immune cells is captured in all samples. This protocol can, therefore, serve as a reference for a documented and reproducible sampling strategy for lymph node transcriptomics.
In the preparation of RNA from tissues, there are multiple key steps for procedural decision-making. First, the methodological literature is mixed in terms of the use of preservation solutions&#160;vs.&#160;the use of flash-frozen tissue samples (and subsequent cold-temperature grinding). Especially in the case of large animal necropsies, there are multiple potential procedural benefits to the use of a preservation solution, as incorporated in this protocol. First, tissue samples can be stored during the necropsy in preservation solution without the need to immediately transfer the tubes to liquid nitrogen. Second, the use of a preservation solution provides additional protection prior to sample processing for RNA extraction, particularly if the sample partially or briefly thaws before homogenization. The results in&#160;Figure 6A&#160;indicate that this protective effect extends to lymph node tissue. In contrast, flash-frozen samples must be maintained in the frozen state until the moment of homogenization in a phenol-containing buffer. Finally, for field necropsies of large animals, where liquid nitrogen is not readily available, samples can be stored in preservation solution until they can be returned to the lab.
Additional advantages of the molecular components of the procedure presented here include the presence of phenol during the initial tissue processing, which serves as a disinfectant during the aerosol-generating process of homogenization for samples from infected animals, and the use of the spin column procedure to remove residual phenol and guanidine isothiocyanate from the sample. The representative results demonstrate that the procedure generates high-quality RNA as assessed by A260/A280&#160;and A260/A230&#160;ratios, gel electrophoresis, and RIN scores, and is robust in the face of time course challenges of livestock and wildlife sampling. The pairing of tissue preservation (e.g., in RNALater), homogenization in phenol-based reagents (e.g., TRIzol), and silica column purification has been successfully utilized in the literature to profile gene expression patterns in ovine abomasal lymph nodes infected with gastrointestinal nematodes46&#160;and in cattle lymph nodes infected with a herpesvirus47, with RIN scores greater than 8 and greater than 7 across all samples, respectively.
In the case of a resulting RNA with unacceptable RIN scores for downstream analysis, the following variables, which are standard for RNA processing, should be assessed: the total processing time post-mortem, the condition of the tissues, the processing time/delay post-thaw, the technique during the RNA extraction, and the RNA handling post-extraction. The total processing time post-mortem should be assessed especially in the case of tissues recovered from animals found dead, as opposed to euthanized animals. As described above, RNA is relatively stable in lymph nodes, but long delays in processing could lead to degradation, especially for unstable transcripts. A confounding time variable could be present if samples are compared between carcasses that have remained in the field for disparate amounts of time. The condition of the tissues should be assessed, because the degradation of tissue integrity, due to pathologic changes associated with infection, may reduce the RNA stability. For example, lower RNA quality has been observed in the placentome of&#160;Brucella-infected animals post-abortion (Boggiatto&#160;et al., submitted). The processing time/delay post-thaw is mitigated by the use of preservation solutions, as described in this protocol. Be certain that the thickness of the tissue pieces is low enough to allow a proper and rapid penetration of the preservative solution into the tissue (&#60; 5 mm thickness using the preservative mentioned in the&#160;Table of Materials). During the RNA extraction, the buffers should be RNase-free and contact with gloves and other contaminated items (RNases are present on the skin) must be avoided. For the grinding of the lymph node tissue, the largest source of potential RNases will be in the tissue itself, but it is beneficial to reduce the introduction of contaminants at all stages of the procedure. To handle the RNA post-extraction, as described in the protocol, aliquot the RNA samples into tubes before the freezing and storage at -80&#176; C, to eliminate the need to freeze-thaw the samples for a quality and quantity analysis.
Low yields in the procedure, in addition to resulting from the degradation of RNA samples, can be due to an inefficient homogenization of lymph node tissue at step 4.3 in the protocol. Note that the incubation in an RNA preservation solution can change the texture of the tissue (increase firmness), although most lymph node tissues dissociated effectively in pilot runs with the large toothed rotor-stator dissociator described here. As noted in step 4.3.1, the homogenization in phenol-based reagent should be repeated if the dissociation is incomplete. Mortar-and-pestle grinding, followed by a resuspension of the ground sample in a phenol-based reagent, is another alternative for laboratories without access to a homogenizer with these specifications. However, a homogenization in disposable tubes presents multiple potential advantages over the grinding of frozen tissue in a mortar and pestle, including a more feasible and shorter workflow for processing multiple samples, an absence of sample loss when grinding, no cleanup, and no potential contact with powered samples, in the case of tissues from infected animals.
Avraham&#160;et al.48&#160;describe that a large 5S RNA peak in the final RNA product, paired with a low recovery of 28S and 18S ribosomal RNAs, can be a sign of an incomplete lysis of the cells (which in turn, for lymph node processing, can be due to an incomplete dissociation of the tissue).&#160;Figure 6B&#160;provides an example of an RNA profile generated from a piece of bovine parotid lymph node that was very high in connective tissue and did not homogenize effectively. RNA yields should be calculated and monitored across samples in a set for analysis to confirm that similar recoveries are obtained per mg of tissue, and samples for direct comparison by RNA-sequencing should be processed in batch, using the same homogenization strategy for all samples. Note that the wedge sampling approach also aids in avoiding a collection of a sample that is exclusively a region of extensive connective tissue.

RNA-sequencing analysis of the transcriptome of lymph nodes provides the opportunity to characterize the immune response of animals to a variety of pathogens. While this methodology has been utilized extensively in mice, analyses have recently been expanding into larger mammals1,2. Livestock/large animal lymph nodes can be used to characterize host responses to an infection, not only for their use in vaccine or genetic susceptibility studies and for the identification of targets for drug development, but also as model systems for human studies on zoonotic diseases. For example, in the case of brucellosis (a zoonotic bacterial disease that impacts half a million people around the world each year), despite significantly increased costs, studies in sheep or goats are more relevant to the human infection and human vaccine development than laboratory animal models. Mouse infection models recapitulate the reticuloendothelial system infection but not the characteristic clinical signs3. 
In large animal experiments as compared to laboratory animal studies, the process of tissue harvesting necessarily involves a longer delay between the euthanasia and the tissue collection, which presents a potential challenge for the preservation of high-quality RNA. Intact RNA is essential for the generation of biologically relevant transcriptomic data. The generation of high-quality RNA from tissue samples is particularly critical for large animal pathogen studies conducted in containment facilities. Such studies are inherently more difficult to perform as they not only require approved facilities and highly trained personnel but also carry significant financial costs, which, depending on the work, can range from tens to hundreds of thousands of dollars. These types of studies also involve a cross-disciplinary collaboration and cross-disciplinary knowledge for their completion, adding to their complexity. Therefore, training on, development of, and adherence to a streamlined system for the sample collection and preservation provides significant benefits for downstream molecular studies of tissues from infected animals.
The collection of larger lymph nodes presents additional challenges for the tissue collection compared to the similar sampling of murine lymph nodes. The preparation for the sample excision necessitates a basic understanding of the anatomy of the lymph node, including the relevant internal structures. The structure of a lymph node is comprised&#160;of lymphoid lobules surrounded by sinuses filled with lymph. These structures are enclosed within a tough, fibrous capsule.4 A lymphoid lobule is the &#34;basic anatomical and functional unit of the lymph node&#34; and is composed of follicles, a deep cortical unit, and medullary cords and sinuses4 (Figure&#160;1A). B and T lymphocytes are home to the follicles and deep cortical units, respectively. These structures provide a 3D scaffold and facilitate the interaction between the lymphocytes and antigen or antigen presenting cells.
Grossly, follicles and deep cortical units can be identified on cut surface as they contain a denser reticular meshwork and appear darker than the sinuses, which are comprised of a more delicate reticular meshwork and appear lighter (Figure 1B). By convention, pathologists refer to the regions of the lymph nodes as the superficial cortex (follicles), the paracortex (deep cortical units) and the medulla (medullary cords and sinuses). A proper examination of all three regions has been deemed as best practice in routine pathological examination guidelines for lymph nodes5. Note that there is a considerable variation in the consistency, size, and color of lymph nodes, even within a single animal. As animals age, their lymph nodes will tend to decrease in size and become firmer than those of younger animals, typically due to an increase in their connective tissue and a reduction of the normal lymphoid structure6,7.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57195/57195fig1.jpg" /> 
Figure 1.&#160;Anatomy of the lymph node. (A) This cartoon image shows the anatomy of the lymph node, depicting key structures. (B)&#160;This still image shows a bovine lymph node cut in cross-section. The relevant structures/layers that are visible to the naked eye are highlighted. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57195/57195fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Depending on the experimental question, different lymph nodes will be of interest for the collection and analysis. Peripheral lymph nodes are those located deep in the subcutaneous tissue. In cattle, peripheral or superficial lymph nodes often used in clinical and experimental practice include parotid, submandibular, retropharyngeal, prescapular, prefemoral (precrural) and superficial inguinal (supramammary in females, scrotal in males) (Figure 2). In Table 1, the properties of key superficial lymph nodes, as described in the cattle system8, are outlined. Below, some potential lymph node collection plans for infectious bacterial diseases of cattle are presented as a starting point for the investigation.
Brucella abortus/Brucella melitensis: Standard necropsies for B. abortus-infected cattle and B. melitensis-infected goats at the National Animal Disease Center recover supramammary, prescapular, and parotid lymph node tissue, both for the grinding for the bacterial enumeration and for the RNA preparation for the host RNA expression profiling. B. abortus can be regularly recovered in each of these lymph nodes in experimentally infected cattle9. The presence of bacteria in each of these lymph node types can be detected in B. melitensis-infected goats up to at least nine months post-infection using the RNA-based methodologies from our studies (Boggiatto et al., unpublished). Salmonella sp.: The prescapular, subiliac (prefemoral), and mesenteric lymph nodes have been useful during the profiling of cattle carcasses for a Salmonella prevalence10,11,12 and would be of potential interest for transcriptomic studies. E. coli O157:H7: Mesenteric lymph nodes (at the middle small intestine and distal small intestine locations) can be the sites of an occasional recovery of the bacteria in infected calves (but not in infected adult cattle)13. Leptospirosis (Leptospira sp.): A chronic persistence of the bacteria has been observed in the lymph nodes draining the mammary gland14. Mycobacterium bovis: In cattle, the bacteria have been recovered post-experimental infection from the mediastinal and tracheobronchial lymph nodes of calves15. Additionally, lymph node RNA has been utilized to examine large animal host responses to viruses, such as the porcine reproductive and respiratory syndrome virus2. Figure 2 depicts the location of a subset of these major lymph nodes in the cattle body.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57195/57195fig2.jpg" /> 
Figure 2: Cartoon depicting selected lymph node locations in Bos taurus. The numbered lymph nodes are annotated. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57195/57195fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In this paper and the associated video, we present a protocol for the isolation of large animal lymph nodes for RNA studies, designed to be informative for molecular biologists involved in transcriptomic studies of large animal infections. First, we provide an overview of the isolation procedure for the lymph nodes, using sampling from bovine and bison tissues as examples. Paired with this demonstration, as displayed in the video, is a workflow for a reproducible tissue sampling for RNA isolation. Next, we describe important considerations for the processing of an infected lymph node, with a focus on safety, consistency, and RNA quality.
The preparation of RNA from the tissue with an acidified phenol-guanidine isothiocyanate reagent is based on the original method of Chomczynski and Sacchi16,17, with a purification over silica-based spin columns in the presence of chaotropic agents based on the original work of Vogelstein and Gillespie18. We also examine the potential for the recovery of RNA for transcriptomics from cattle lymph nodes preserved by alternative methods. Finally, we explore the impact of the time variable on the RNA quality in large animal necropsies, including a representative experiment depicting the effect of an increase in time between the euthanasia and the sampling on the recovered RNA profile from bison and bovine lymph nodes. This article will be useful not only to molecular biologists but also to veterinary researchers commencing transcriptomic studies.

<table border="0" cellpadding="0" cellspacing="0" style="width:1239px;" width="1240">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">RNA preservation solution (we used RNALater for all experiments)</td>
			<td style="width:167px;">ThermoFisher</td>
			<td style="width:119px;">AM7020</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1.5 ml or 2 ml polypropylene microcentrifuge tubes&#160;</td>
			<td style="width:167px;">Fisher Scientific</td>
			<td style="width:119px;">05-408-129</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Disposable scalpels</td>
			<td style="width:167px;">Daigger Scientific</td>
			<td style="width:119px;">EF7281</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tissue forceps, rat tooth</td>
			<td style="width:167px;">Fisher Scientific</td>
			<td style="width:119px;">12-460-117</td>
			<td>Other tissue forceps available including curved tip, tapered edge, etc. , depends on user preference</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">3 mm punch biopsy needles</td>
			<td style="width:167px;">Fisher Scientific</td>
			<td style="width:119px;">NC9949469</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sharps container (small and transportable for necropsy)</td>
			<td style="width:167px;">Stericycle</td>
			<td style="width:119px;">8900SA</td>
			<td>1 qt. size shown here</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cutting boards or disposable trays</td>
			<td style="width:167px;">Fisher Scientific</td>
			<td style="width:119px;">09-002-24A</td>
			<td>Available in a variety of sizes, depends on user preference</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Personal protective equipment</td>
			<td style="width:167px;"></td>
			<td style="width:119px;"></td>
			<td>Varies with pathogen (gloves, respirator masks, goggles, etc.)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Phenol-based RNA extraction reagent (we used TRIzol Reagent for all experiments)</td>
			<td style="width:167px;">ThermoFisher</td>
			<td style="width:119px;">15596026</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Silica column-based RNA extraction kit (we used the PureLink RNA Mini kit for all experiments)</td>
			<td style="width:167px;">ThermoFisher</td>
			<td style="width:119px;">12183018A</td>
			<td>Designed for up to 100 mg tissue</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">100% Ethanol (200 proof for molecular biology)</td>
			<td style="width:167px;">Sigma-Aldrich</td>
			<td style="width:119px;">E7023</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tissue homogenizer with enclosed homogenization tubes (we used the gentleMACS dissociator for all experiments)</td>
			<td style="width:167px;">Miltenyi Biotec</td>
			<td style="width:119px;">130-093-235</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Agarose (General, for gel electrophoresis)</td>
			<td style="width:167px;">Sigma-Aldrich</td>
			<td style="width:119px;">A9539</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">1X TBE</td>
			<td style="width:167px;">Fisher Scientific</td>
			<td style="width:119px;">BP24301</td>
			<td>Can also make from scratch in the laboratory</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">Deionized formamide</td>
			<td style="width:167px;">EMD Millipore</td>
			<td style="width:119px;">S4117</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">Sodium dodecyl sulfate</td>
			<td style="width:167px;">Sigma-Aldrich</td>
			<td style="width:119px;">L3771</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">Bromophenol blue</td>
			<td style="width:167px;">Sigma-Aldrich</td>
			<td style="width:119px;">114391</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">Xylene cyanol&#160;</td>
			<td style="width:167px;">Sigma-Aldrich</td>
			<td style="width:119px;">X4126</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">EDTA (Ethylenediaminetetraacetic acid)</td>
			<td style="width:167px;">Sigma-Aldrich</td>
			<td style="width:119px;">EDS</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">UV-Vis Spectrophotometer (we used the NanoDrop Spectrophotometer)</td>
			<td style="width:167px;">ThermoFisher</td>
			<td style="width:119px;">ND-2000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">Device for quantitative RNA assessment (we used the Bioanalyzer, with associated components and protocols)</td>
			<td style="width:167px;">Agilent</td>
			<td style="width:119px;">G2939BA</td>
			<td></td>
		</tr>
		<tr height="54">
			<td height="54" style="height:54px;width:787px;">FFPE RNA extraction kit (we used the RecoverAll Total Nucleic Acid Isolation Kit for Formalin Fixed, Paraffin Embedded Tissue)</td>
			<td style="width:167px;">ThermoFisher</td>
			<td style="width:119px;">AM1975</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">Plastic spreader (L-shaped spreader)</td>
			<td style="width:167px;">Fisher Scientific</td>
			<td style="width:119px;">14-665-231</td>
			<td>Only needed for sterility testing for samples from infected animals</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:787px;">Necropsy knives</td>
			<td style="width:167px;">Livestock Concepts</td>
			<td style="width:119px;">WI-0009209</td>
			<td></td>
		</tr>
	</tbody>
</table>

collection and processing of lymph nodes from large animals for rna analysis: preparing for lymph node transcriptomic studies of large animal species

Large animals (both livestock and wildlife) serve as important reservoirs of zoonotic pathogens, including Brucella, Mycobacterium bovis, Salmonella, and E. coli, and are useful for the study of pathogenesis and/or spread of the bacteria in natural hosts. With the key function of lymph nodes in the host immune response, lymph node tissues serve as a potential source of RNA for downstream transcriptomic analyses, in order to assess the temporal changes in gene expression in cells over the course of an infection. This article presents an overview of the process of lymph node collection, tissue sampling, and downstream RNA processing in livestock, using cattle (Bos taurus) as a model, with additional examples provided from the American bison (Bison bison). The protocol includes information about the location, identification, and removal of lymph nodes from multiple key sites in the body. Additionally, a biopsy sampling methodology is presented that allows for a consistency of sampling across multiple animals. Several considerations for sample preservation are discussed, including the generation of RNA suitable for downstream methodologies like RNA-sequencing and RT-PCR. Due to the long delays inherent in large animal vs. mouse time course studies, representative results from bison and bovine lymph node tissues are presented to describe the time course of the degradation in this tissue type, in the context of a review of previous methodological work on RNA degradation in other tissues. Overall, this protocol will be useful to both veterinary researchers beginning transcriptome projects on large animal samples and to molecular biologists interested in learning techniques for in vivo tissue sampling and in vitro processing.

Watch this Scientific Journal Video about Collection and Processing of Lymph Nodes from Large Animals for RNA Analysis: Preparing for Lymph Node Transcriptomic Studies of Large Animal Species at JoVE.

Collection and Processing of Lymph Nodes from Large Animals for RNA Analysis: Preparing for Lymph Node Transcriptomic Studies of Large Animal Species

This protocol provides an overview of procedures for the isolation of RNA for the transcriptomic profiling of lymph node tissues from large animals, including steps in the identification and excision of lymph nodes from livestock and wildlife, sampling approaches to provide consistency across multiple animals, and considerations plus representative results for the post-collection preservation and processing for RNA analysis.

Large animals (both livestock and wildlife) serve as important reservoirs of zoonotic pathogens, including Brucella, Mycobacterium bovis, Salmonella, and ...

collection-processing-lymph-nodes-from-large-animals-for-rna-analysis

Nanyang Technological University

Research

JoVE Journal

Immunology and Infection

26.0K Views.  U.S. Department of Agriculture. This protocol provides an overview of procedures for the isolation of RNA for the transcriptomic profiling of lymph node tissues from large animals, including steps in the identification and excision of lymph nodes from livestock and wildlife, sampling approaches to provide consistency across multiple animals, and considerations plus representative results for the post-collection preservation and processing for RNA analysis.

Video: Collection and Processing of Lymph Nodes from Large Animals for RNA Analysis: Preparing for Lymph Node Transcriptomic Studies of Large Animal Species

Intravital Microscopy of the Inguinal Lymph Node

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

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

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

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, ...

Ex vivo Imaging of T Cells in Murine Lymph Node Slices with Widefield and Confocal Microscopes

Na&iuml;ve T cells continuously traffic to secondary lymphoid organs, including peripheral lymph nodes, to detect rare expressed antigens. The migration of T cells into lymph nodes is a complex process which involves both cellular and chemical factors including chemokines. Recently, the use of two-photon microscopy has permitted to track T cells in intact lymph nodes and to derive some quantitative information on their behavior and their interactions with other cells. While there are obvious advantages to an in vivo system, this approach requires a complex and expensive instrumentation and provides limited access to the tissue. To analyze the behavior of T cells within murine lymph nodes, we have developed a slice assay 
1, originally set up by neurobiologists and transposed recently to murine thymus 2. In this technique, fluorescently labeled T cells are plated on top of an acutely prepared lymph node slice. In this video-article, the localization and migration of T cells into the tissue are analyzed in real-time with a widefield and a confocal microscope. The technique which complements in vivo two-photon microscopy offers an effective approach to image T cells in their natural environment and to elucidate mechanisms underlying T cell migration.

Ex vivo Imaging of T Cells in Murine Lymph Node Slices with Widefield and Confocal Microscopes

This protocol describes a method to image fluorescent T cells introduced into lymph node slices. The technique permits real-time analyses of T cell migration with traditional widefield fluorescence or confocal microscopes.

Na&iuml;ve T cells continuously traffic to secondary lymphoid organs, including peripheral lymph nodes, to detect rare expressed antigens. The migration ...

Murine Superficial Lymph Node Surgery

In the field of immunology, to understand the progression of an immune response against a vaccine, an infection or a tumour, the response is often followed over time. Similarly, the study of lymphocyte homeostasis requires time course experiments. Performing these studies within the same mouse is ideal to reduce the experimental variability as well as the number of mice used. Blood withdrawal allows performance of time course experiments, but it only gives information about circulating lymphocytes and provides a limited number of cells1-4. Since lymphocytes circulating through the body and residing in the lymph nodes have different properties, it is important to examine both locations. The sequential removal of lymph nodes by surgery provides a unique opportunity to follow an immune response or immune cell expansion in the same mouse over time. Furthermore, this technique yields between 1-2x106 cells per lymph node which is sufficient to perform phenotypic characterization and/or functional assays. Sequential lymph node surgery or lymphadenectomy has been successfully used by us and others5-11. Here, we describe how the brachial and inguinal lymph nodes can be removed by making a small incision in the skin of an anesthetised mouse. Since the surgery is superficial and done rapidly, the mouse recovers very quickly, heals well and does not experience excessive pain. Every second day, it is possible to harvest one or two lymph nodes allowing for time course experiments. This technique is thus suitable to study the characteristics of lymph node-residing lymphocytes over time. This approach is suitable to various experimental designs and we believe that many laboratories would benefit from performing sequential lymph node surgeries.

To follow the progression of an immune response over time within the same mouse, lymph nodes can be sequentially removed by surgery. Here, we describe how this technique can be performed.

In the field of immunology, to understand the progression of an immune response against a vaccine, an infection or a tumour, the response is often ...

Intravital Imaging of the Mouse Popliteal Lymph Node

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

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

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

Generation of Lymph Node-fat Pad Chimeras for the Study of Lymph Node Stromal Cell Origin

The stroma is a key component of the lymph node structure and function. However, little is known about its origin, exact cellular composition and the mechanisms governing its formation. Lymph nodes are always encapsulated in adipose tissue and we recently demonstrated the importance of this relation for the formation of lymph node stroma. Adipocyte precursor cells migrate into the lymph node during its development and upon engagement of the Lymphotoxin-b receptor switch off adipogenesis and differentiate into lymphoid stromal cells (B&#233;n&#233;zech&#160;et al.14). Based on the lymphoid stroma potential of adipose tissue, we present a method using a lymph node/fat pad chimera that allows the lineage tracing of lymph node stromal cell precursors. We show how to isolate newborn lymph nodes and EYFP+ embryonic adipose tissue and make a LN/ EYFP+ fat pad chimera. After transfer under the kidney capsule of a host mouse, the lymph node incorporates local adipose tissue precursor cells and finishes its formation. Progeny analysis of EYFP+ fat pad cells in the resulting lymph nodes can be performed by flow-cytometric analysis of enzymatically digested lymph nodes or by immunofluorescence analysis of lymph nodes cryosections. By using fat pads from different knockout mouse models, this method will provide an efficient way of analyzing the origin of the different lymph node stromal cell populations.

Generation of lymph node/fat pad chimeras for the study of lymph node stromal cell origin is described. The method involves the isolation of lymph nodes from newborn mice and embryonic fat pads, the generation of chimeric lymph node-fat pads, and their transfer under the kidney capsule of a host mouse.

The stroma is a key component of the lymph node structure and function. However, little is known about its origin, exact cellular composition and the ...

Analysis of the Epithelial Damage Produced by Entamoeba histolytica Infection

Entamoeba histolytica is the causative agent of human amoebiasis, a major cause of diarrhea and hepatic abscess in tropical countries. Infection is initiated by interaction of the pathogen with intestinal epithelial cells. This interaction leads to disruption of intercellular structures such as tight junctions (TJ). TJ ensure sealing of the epithelial layer to separate host tissue from gut lumen. Recent studies provide evidence that disruption of TJ by the parasitic protein EhCPADH112 is a prerequisite for E. histolytica invasion that is accompanied by epithelial barrier dysfunction. Thus, the analysis of molecular mechanisms involved in TJ disassembly during E. histolytica invasion is of paramount importance to improve our understanding of amoebiasis pathogenesis. This article presents an easy model that allows the assessment of initial host-pathogen interactions and the parasite invasion potential. Parameters to be analyzed include transepithelial electrical resistance, interaction of EhCPADH112 with epithelial surface receptors, changes in expression and localization of epithelial junctional markers and localization of parasite molecules within epithelial cells.

Analysis of the Epithelial Damage Produced by Entamoeba histolytica Infection

Human infection by Entamoeba histolytica leads to amoebiasis, a major cause of diarrhea in tropical countries. Infection is initiated by pathogen interactions with intestinal epithelial cells, provoking the opening of cell-cell contacts and consequently diarrhea, sometimes followed by liver infection. This article provides a model to assess the early host-pathogen interactions to improve our understanding of amoebiasis pathogenesis.

Entamoeba histolytica is the causative agent of human amoebiasis, a major cause of diarrhea and hepatic abscess in tropical countries. Infection is ...

Isolation of Murine Lymph Node Stromal Cells

Secondary lymphoid organs including lymph nodes are composed of stromal cells that provide a structural environment for homeostasis, activation and differentiation of lymphocytes. Various stromal cell subsets have been identified by the expression of the adhesion molecule CD31 and glycoprotein podoplanin (gp38), T zone reticular cells or fibroblastic reticular cells, lymphatic endothelial cells, blood endothelial cells and FRC-like pericytes within the double negative cell population. For all populations different functions are described including, separation and lining of different compartments, attraction of and interaction with different cell types, filtration of the draining fluidics and contraction of the lymphatic vessels. In the last years, different groups have described an additional role of stromal cells in orchestrating and regulating cytotoxic T cell responses potentially dangerous for the host. 
Lymph nodes are complex structures with many different cell types and therefore require a appropriate procedure for isolation of the desired cell populations. Currently, protocols for the isolation of lymph node stromal cells rely on enzymatic digestion with varying incubation times; however, stromal cells and their surface molecules are sensitive to these enzymes, which results in loss of surface marker expression and cell death. Here a short enzymatic digestion protocol combined with automated mechanical disruption to obtain viable single cells suspension of lymph node stromal cells maintaining their surface molecule expression is proposed.

Isolation of lymph node stromal cells is a multistep procedure including enzymatic digestion and mechanical disaggregation to obtain fibroblastic reticular cells, lymphatic and blood endothelial cells. In the described procedure, a short digestion is combined with automated mechanical disaggregation to minimize surface marker degradation of viable lymph node stromal cells.

Secondary lymphoid organs including lymph nodes are composed of stromal cells that provide a structural environment for homeostasis, activation and ...

Myeloid Cell Isolation from Mouse Skin and Draining Lymph Node Following Intradermal Immunization with Live Attenuated Plasmodium Sporozoites

Malaria infection begins when the sporozoite stage of Plasmodium is inoculated into the skin of a mammalian host through a mosquito bite. The highly motile parasite not only reaches the liver to invade hepatocytes and transform into erythrocyte-infective form. It also migrates into the skin and to the proximal lymph node draining the injection site, where it can be recognized and degraded by resident and/or recruited myeloid cells. Intravital imaging reported the early recruitment of brightly fluorescent Lys-GFP positive leukocytes in the skin and the interactions between sporozoites and CD11c+ cells in the draining lymph node. We present here an efficient procedure to recover, identify and enumerate the myeloid cell subsets that are recruited to the mouse skin and draining lymph node following intradermal injection of immunizing doses of sporozoites in a murine model. Phenotypic characterization using multi-parametric flow cytometry provides a reliable assay to assess early dynamic cellular changes during inflammatory response to Plasmodium infection.

Myeloid Cell Isolation from Mouse Skin and Draining Lymph Node Following Intradermal Immunization with Live Attenuated Plasmodium Sporozoites

We describe here a protocol for isolating myeloid cells from mouse skin and draining lymph node following intradermal injection of Plasmodium sporozoites. Flow cytometry of collected cells provides a reliable assay to characterize the skin and draining lymph node inflammatory response to the parasite.

Malaria infection begins when the sporozoite stage of Plasmodium is inoculated into the skin of a mammalian host through a mosquito bite. The highly ...

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 ...