The deep cortex of the lymph node: morphological variations and functional aspects

Histomolecular Structural Aspects of High Endothelial Vessels in Lymph Node and Its Significance in Oral Cancer and Metastasis

Molecular cancer research studies focus on identifying diagnostic, screening, and metastatic indicators, and monitoring therapeutic responses. Migration of tumor cells and lymphocytes are important aspects in metastasis. High endothelial vessels are specialized histological structures identified in the blood vessels in lymphoid organs, which allow the migration of lymphocytes. In the recent decades, the role of high endothelial vessels is being addressed in cancer metastatic research. This review article is to highlight the histological and molecular structural aspects of high endothelial venules (HEVs) in the lymph node, and to demonstrate the role of HEVs in oral cancer metastasis, specifically oral and pharyngeal squamous cell carcinoma. The literature for the present paper were searched from the data sources such as Medline/PubMed, CINAHL plus, and gray literature sources from inception to May 2015. Searches were conducted using both free texts and medical subject headings related to the title of the present paper. Only the full text manuscripts of the search results that support the objective(s) of the paper and papers written in English were included. HEVs are unique structures that are identified in the lymphocytes and primarily assist in the lymphocytic migration from the blood stream into the lymph node. Understanding the histomolecular characteristics of HEV will allow researchers to develop novel therapeutic approaches in cancer tissues.

Morphological studies of lymphatic labyrinths in the rat mesenteric lymph node

To supplement and correct the morphological features of lymphatic labyrinths (LLs) in rat mesenteric lymph node, the distribution, morphology and origin of LLs, and cellular elements in LLs, particularly the organization and integrity of the wall of LLs were examined by silver impregnation, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and immunohistochemistry. LLs consisted of labyrinthine tubules and ran through not only the periphery of the deep cortical unit (DCU) but interfollicular cortex. LLs originated at the edge of the center of the DCU and of the follicle. At the site of their origin, the fibers in the wall of LL were continuous with the fibers located in the follicle and the center of DCU. The wall of LLs was a trilaminar membrane: a layer of flattened lymphatic endothelium; a layer of fibroblastic reticular cells; and amorphous substance and collagen fibers sandwiched between the above two layers. Under SEM and TEM, the whole amoeboid lymphocytes were moving through the pores in the wall of LL, which showed that lymphocytes end their journey through the paracortical cord by migrating into LLs. Immunohistochemical lymphatic vessel endothelial hyaluronan receptor-1 expression was present in cells lining the LLs and intraluminal stellate cells, which may belong to the "sinus endothelial/virgultar cells." LLs are specific channels that are different from lymphatic sinuses. LL may be regarded as a special part of lymphatic vascular system in lymph nodes. We confirm that LLs are important transport pathway of lymphocytes in lymph nodes. The structural framework of LLs facilitates the migration of lymphocytes.

Normal structure, function, and histology of lymph nodes

Lymph nodes are traditionally regarded as having three compartments, the cortex, paracortex and medulla. B and T cells home to separate areas within these compartments, interact with antigen presenting cells, and undergo clonal expansion. This paper provides structural and functional details about how the lymph node brings lymphocytes and antigen presenting cells together. The concept of the lymphoid lobule as the basic functional and anatomic unit of the lymph node is developed and utilized to provide a framework for understanding lymph node pathobiology. Understanding the histomorphologic features of the lymphoid lobule and the role of the reticular meshwork scaffolding of the lymph node and how these related to the cortex, paracortex and medulla provides a unique approach to understanding lymph node structure and function.

Natural bovine lentivirus type 1 infection in Holstein dairy cattle. II. Lymphoid tissue lesions

Bovine immunodeficiency virus (BIV) in Holstein cows was associated with morphologic evidence of lymphoid organ deficiency. Cows were subjected to normal management practices including parturition and lactation without adverse environmental stresses. During the clinical disease process there was marked weight loss and wasting with frequent and severe concurrent infections. Lymphoid follicular hyperplasia and dysplasia in lymph nodes, and hypertrophy and hyperplasia in hemal lymph nodes were characteristics of the lymphoid tissues. Atrophy of lymphoid cell compartments with depletion of lymphocytes and a lymphocytic lymphoid folliculitis were components of the lymphoid system pathology. The nodal tissue lesions resembled those observed in feline, simian, and human lentiviral disease. A functional correlation with immune system deficiency was the development of multiple bacterial infections which failed to resolve after appropriate therapy. The BIV-associated disease syndrome in dairy cows may be useful as a model system for investigation of the pathogenesis of the lymphoid organ changes that occur in humans and animals with lentiviral infection.

Localisation of CD25+ cells and MHCII+ cells in lymph nodes draining Mycobacterium avium subsp. paratuberculosis vaccination granuloma and the presence of a systemic immune response

Vaccination of goat kids against paratuberculosis protects against lesions and clinical disease. The systemic cellular response was studied in goat kids 3-9 weeks after vaccination. Peripheral blood cells showed increased interferon-gamma production and expression of interleukin-2 receptor (CD25) after stimulation with Mycobacterium avium subsp. paratuberculosis antigens. The lymph node draining the vaccination granuloma was studied three weeks after vaccination in a parallel group of goat kids. In deep cortex, MHCII+ cells were observed surrounded by CD4+ T-cells, while follicular hypertrophy and hyperplasia were prominent in the subcapsular region and along connective tissue trabecula. Comparison of the local and systemic immune responses revealed an inverse relationship between CD25+ T-cells in the lymph node deep cortex and cells in peripheral blood that up-regulate CD25 upon in vitro stimulation, suggesting that activated and regulatory T-cells in the local lymph node influence the level of circulating antigen-specific T-cells following vaccination against paratuberculosis in goats.

The morphology, immunophenotype and distribution of paracortical dendritic leucocytes in lymph nodes regional to cutaneous melanoma

Our aim was to identify and delineate alterations in the distribution and immunophenotype of the lymphocytes and paracortical dendritic leucocytes (interdigitating dendritic cells; IDCs) in lymph nodes regional to tumours. Using immunocytochemistry and computer-assisted image analysis we examined 65 lymph nodes excised from 47 patients with malignant melanoma. Twenty-nine patients had American Joint Committee on Cancer (AJCC) stage II melanoma (no tumour spread beyond the primary site) and 18 had AJCC stage III disease (metastases in the regional nodes). There were significant differences in the frequency, morphology, immunophenotype and anatomical distribution of the IDCs and in the complexity of their dendritic processes in different areas within individual lymph nodes. We conclude that morphological and phenotypical variations in IDCs correlate with differing levels of antigen presentation. Downregulation of antigen presentation in lymph nodes regional to tumours is most probably mediated by tumour products. Differences in IDC distribution and characteristics in lymph nodes from different anatomical sites must be considered in interpreting studies of nodal morphology and function.

Histopathologic approaches to detect changes indicative of immunotoxicity

Toxicologic pathology is crucial in the identification and characterization of health effects following exposure to xenobiotics, mainly in toxicity experiments in rodents. Regarding regulatory toxicology, histopathology of lymphoid organs and tissues is a cornerstone in the identification of immunotoxic compounds. A 2-tier testing system is usually employed in which the first tier is a general screen for (immuno)toxicity and the second tier consists of specific immune function studies, including host resistance tests or mechanistic studies. The role attributed to histopathology of lymphoid organs in the updated Organisation for Economic Cooperation and Development and Food and Drug Administration guidelines requires improvement and standardization of the histopathology procedures. Optimalization and standardization was started in an international collaborative immunotoxicity study (ICICIS). However, several problems were left unaddressed, mostly because of the few compounds tested in this study. Based on the results of the ICICIS study and the morphologic changes induced by immunotoxic/immunomodulatory compounds observed in other investigations, suggestions are given to further improve the identification and (semi)quantification of histopathologic changes in lymphoid organs and tissues.

Increased gammadelta T-cell populations in draining lymph nodes of lambs during the elicitation phase of dinitrochlorobenzene-induced contact hypersensitivity

Ten lambs were sensitised with the hapten DNCB in an acetone/olive oil vehicle. The hapten/vehicle solution was applied onto the skin on the shaved ventral surface of the right ear. Two weeks later these lambs were rechallenged with the DNCB/vehicle solution. Simultaneously, ten non-sensitised lambs were treated with vehicle only, serving as vehicle controls. The 20 lambs were slaughtered 48 h after challenge/vehicle treatment, along with ten untreated animals serving as normal controls. Specimens of draining lymph nodes were collected from the 30 animals. All lambs were between 149 and 187 days old. Lymph node cryosections were stained for several leukocyte markers using monoclonal antibodies with the ABC immunohistochemical method. The stained sections were subsequently assessed in three different cortical compartments in each section, using an image analysis system. The resulting measurements from the three groups were compared. A marked increase of gammadelta T cells was detected in the DNCB group. The number of CD4+ T helper cells was decreased in the DNCB group compared with the normal control group, but not with the vehicle control group. No differences were revealed for CD8+ T cytotoxic cells or B cells. These findings were interpreted to be the consequences of possible downregulatory mechanisms protecting the lymphoid tissue from hypersensitivity. The prominence of gammadelta T-cells could indicate that these cells are involved in downregulation.

Cords, channels, corridors and conduits: critical architectural elements facilitating cell interactions in the lymph node cortex

The lymph node cortex is a critical site for encounter between recirculating T cells and their specific antigens. Due to its extreme plasticity, little is understood of the underlying functional unit of the lymph node cortex, the paracortical cord. The idealized paracortical cord (approximately 100 microns by 1000 microns) stretches from a medullary cord to the base of a B-cell follicle. In cross-section, a cord can be visualized as a set of nested cylinders consisting of spaces bounded by cells. The spaces are: i) the lumen of the high endothelial venule (HEV), ii) perivenular channels-narrow potential spaces (0.1 micron) tightly encircling the HEV, iii) corridors-broad spaces (10-15 microns) constituting the majority of the parenchyma, and iv) the cortical sinus. In addition to these spaces for cell traffic, the conduit (fifth space) is a special delivery system for the transit of soluble factors to the HEV and emigrating lymphocytes. The cellular barriers between these spaces are high endothelium, fibroblastic reticular cells, or sinus-lining cells. This review describes the spaces of the paracortical cord and their cellular boundaries, outlines the movement of cells and fluids through these spaces, and discusses how this anatomy affects the efficiency of surveillance by T cells.

High endothelial venules of the rat lymph node. A review and a question: is their activity antigen specific?

BACKGROUND

The high endothelial venules (HEVs) of the lymph nodes are sites for transvascular lymphocyte traffic. Due mostly to the wide scale of variations manifested by the HEVs and to frequently restricted conditions of observation, reports often differed on their morphological or functional features, which has led to opposing views on aspects of the functioning of HEVs.

METHODS

In the present review, we analyze previous reports and attempt to derive comprehensive proposals to reconcile variations in actual observations under diverse conditions.

RESULTS

This analysis shows that the features typical of the HEV endothelial cells (HEV cells) are stimulated to emerge by antigens and the proper lymphocytes and mediators. The stimulation would implicate drained lymphocytes migrating in the perivascular channel, immediately cuffing an HEV's endothelium. A marked pleomorphism of HEV cells betrays the fact that they undergo individual stimulation and a somewhat heterogeneous activity. Other facts indicate that the subendothelial spaces of HEV cells are sites of interactions between drained lymphocytes, HEV cells, and recruited blood lymphocytes. Facts also reveal time- and site-related variations in the intensity of recruitment of blood lymphocytes by HEV cells and topographically related variations in the nature of the recruited cells.

CONCLUSIONS

Analysis of some other observations, often ignored, lead to the conclusion that recruitment of lymphocytes by HEV cells for the sake of participating in local specific immune activities is antigen specific, despite the implication of homing receptors of lymphocytes.

A modified silver impregnation technique for the observation of thick sections of lymph nodes perfused with colloidal carbon

For many years, a variant of the silver impregnation technique of Bielchowsky has been used to study the lymph node because it clearly outlines the various structures which are usually hard to contrast with standard staining methods. Like other variants of silver impregnation, this method blackens the cell nuclei as well as the reticular fibers; however, it inhibits the impregnation of the nuclear chromatin immediately adjacent to fibers. Hence, this variant selectively darkens the lymphoid cell populations of the nodal structures which contain a loose fiber network. To study the blood vascular network of the lymph node based on perfusion of colloidal carbon, a staining procedure was needed which would contrast nodal structures on thick sections, while allowing the carbon-filled small blood vessels to be distinguished from the impregnated coarse reticular fibers. In an attempt to adapt this variant of Bielchowsky's technique, 10, 20, 40 and 60 microns thick sections from rat nodes, fixed in a solution of Bouin-Hollande for 72 hr, were silver impregnated with serial dilutions (1:2 to 1:128) of the ammoniacal silver solution. Forty-micrometer thick sections impregnated with a 1:16 dilution of the original silver solution at 37 C and for 30 min provided the best results for the conditions.