Desmoplakin as a specific marker of lymphatic vessels

Immunomodulatory properties of the lymphatic endothelium in the tumor microenvironment

The tumor microenvironment (TME) is an intricate complex and dynamic structure composed of various cell types, including tumor, stromal and immune cells. Within this complex network, lymphatic endothelial cells (LECs) play a crucial role in regulating immune responses and influencing tumor progression and metastatic dissemination to lymph node and distant organs. Interestingly, LECs possess unique immunomodulatory properties that can either promote or inhibit anti-tumor immune responses. In fact, tumor-associated lymphangiogenesis can facilitate tumor cell dissemination and metastasis supporting immunoevasion, but also, different molecular mechanisms involved in LEC-mediated anti-tumor immunity have been already described. In this context, the crosstalk between cancer cells, LECs and immune cells and how this communication can shape the immune landscape in the TME is gaining increased interest in recent years. In this review, we present a comprehensive and updated report about the immunomodulatory properties of the lymphatic endothelium within the TME, with special focus on primary tumors and tumor-draining lymph nodes. Furthermore, we outline emerging research investigating the potential therapeutic strategies targeting the lymphatic endothelium to enhance anti-tumor immune responses. Understanding the intricate mechanisms involved in LEC-mediated immune modulation in the TME opens up new possibilities for the development of innovative approaches to fight cancer.

Corneal Lymphangiogenesis: Current Pathophysiological Understandings and Its Functional Role in Ocular Surface Disease

The cornea is a transparent and avascular tissue that plays a central role in light refraction and provides a physical barrier to the external environment. Corneal avascularity is a unique histological feature that distinguishes it from the other parts of the body. Functionally, corneal immune privilege critically relies on corneal avascularity. Corneal lymphangiogenesis is now recognized as a general pathological feature in many pathologies, including dry eye disease (DED), corneal allograft rejection, ocular allergy, bacterial and viral keratitis, and transient corneal edema. Currently, sizable data from clinical and basic research have accumulated on the pathogenesis and functional role of ocular lymphangiogenesis. However, because of the invisibility of lymphatic vessels, ocular lymphangiogenesis has not been studied as much as hemangiogenesis. We reviewed the basic mechanisms of lymphangiogenesis and summarized recent advances in the pathogenesis of ocular lymphangiogenesis, focusing on corneal allograft rejection and DED. In addition, we discuss future directions for lymphangiogenesis research.

The cell-cell junctions of mammalian testes. III. Absence of an endothelial cell layer covering the peritubular wall of the seminiferous tubules-an immunocytochemical correction of a 50-year-old error in the literature

In the molecular biological and ultrastructural studies of the peritubular wall cells encasing the seminiferous tubules of mammalian testes, we found it necessary to characterize the outermost cell layer bordering on the interstitial space in detail. For half a century, the extremely thin cells of this monolayer have in the literature been regarded as part of a lymphatic endothelium, in particular in rodents. However, our double-label immunofluorescence microscopical results have shown that in all six mammalian species examined, including three rodent ones (rat, mouse, guinea pig), this classification is not correct: the very attenuated cells of this monolayer are not of lymphatic endothelial nature as they do not contain established endothelial marker molecules. In particular, they do not contain claudin-5-positive tight junctions, VE-cadherin-positive adherens junctions, "lymph vessel endothelium hyaluronan receptor 1" (LYVE-1), podoplanin, protein myozap and "von Willebrand Factor" (vWF). By contrast and as controls, all these established marker molecules for the lymphatic endothelial cell type are found in the endothelia of the lymph and-partly also-blood vessels located nearby in the interstitial space. Thus, our results provide evidence that the monolayer cells covering the peritubular wall do not contain endothelial marker molecules and hence are not endothelial cells. We discuss possible methodological reasons for the maintenance of this incorrect cell type classification in the literature and emphasize the value of molecular analyses using multiple cell type-specific markers, also with respect to physiology and medical sciences.

The Hepatic Lymphatic Vascular System: Structure, Function, Markers, and Lymphangiogenesis

The lymphatic vascular system has been minimally explored in the liver despite its essential functions including maintenance of tissue fluid homeostasis. The discovery of specific markers for lymphatic endothelial cells has advanced the study of lymphatics by methods including imaging, cell isolation, and transgenic animal models and has resulted in rapid progress in lymphatic vascular research during the last decade. These studies have yielded concrete evidence that lymphatic vessel dysfunction plays an important role in the pathogenesis of many diseases. This article reviews the current knowledge of the structure, function, and markers of the hepatic lymphatic vascular system as well as factors associated with hepatic lymphangiogenesis and compares liver lymphatics with those in other tissues.

Understanding lymphangiogenesis in knockout models, the cornea, and ocular diseases for the development of therapeutic interventions

A major focus of cancer research for several decades has been understand the ability of tumors to induce new blood vessel formation, a process known as angiogenesis. Unfortunately, only limited success has been achieved in the clinical application of angiogenesis inhibitors. We now know that lymphangiogenesis, the growth of lymphatic vessels, likely also plays a major role in tumor progression. Thus, therapeutic strategies targeting lymphangiogenesis or both lymphangiogenesis and angiogenesis may represent promising approaches for treating cancer and other diseases. Importantly, research progress toward understanding lymphangiogenesis is significantly behind that related to angiogenesis. A PubMed search of "angiogenesis" returns nearly 80,000 articles, whereas a search of "lymphangiogenesis" returns 2,635 articles. This stark contrast can be explained by the lack of molecular markers for identifying the invisible lymphatic vasculature that persisted until less than 2 decades ago, combined with the intensity of research interest in angiogenesis during the past half century. Still, significant strides have been made in developing strategies to modulate lymphangiogenesis, largely using ocular disease models. Here we review the current knowledge of lymphangiogenesis in the context of knockout models, ocular diseases, the biology of activators and inhibitors, and the potential for therapeutic interventions targeting this process.

Recent developments in morphology of lymphatic vessels and lymph nodes

This paper reviews the morphology of lymphatics and lymphangiogenesis in vivo, microenvironments that promote lymphangiogenesis, and the structure and function of lymph nodes. Lymphatic capillaries consist of a single layer of lymphatic endothelial cells (LECs) and have valves, while collecting lymphatics are endowed with smooth muscle cells (SMCs) and valves besides a single layer of LECs. In the embryonic rat diaphragm, LECs first migrate presumably according to interstitial fluid flow and later join to form lymphatic vessels. SMCs of the collecting lymphatics are apparently differentiated from mesenchymal cells. LECs cultured on Cell Culture Inserts under a low oxygen condition proliferate very well and form a lymphatic network. LECs cultured on a collagen fiber network with a natural three-dimensional (3D) architecture under low oxygen rapidly form a 3D lymphatic network. The lymph node initiates an immune response as a critical crossroads for the encounter between antigen-presenting cells, antigens from lymph, and lymphocytes recruited into nodes from the blood. The node consists of spaces lined with LECs and parenchyma. High endothelial venules in the node strongly express Aquaporin-1, suggesting their involvement in the net absorption of water from lymph coming through afferent lymphatics. SMCs in node capsules seem to be involved in squeezing out lymphocytes and lymph. (English Translation of J Jpn Col Angiol 2008; 48: 107-112.).

The plaque protein myozap identified as a novel major component of adhering junctions in endothelia of the blood and the lymph vascular systems

Recently the protein myozap, a 54-kD polypeptide which is not a member of any of the known cytoskeletal and junctional protein multigene families, has been identified as a constituent of the plaques of the composite junctions in the intercalated disks connecting the cardiomyocytes of mammalian hearts. Using a set of novel, highly sensitive and specific antibodies we now report that myozap is also a major constituent of the cytoplasmic plaques of the adherens junctions (AJs) connecting the endothelial cells of the mammalian blood and lymph vascular systems, including the desmoplakin-containing complexus adhaerentes of the virgultar cells of lymph node sinus. In light and electron microscopic immunolocalization experiments we show that myozap colocalizes with several proteins of desmosomal plaques as well as with AJ-specific transmembrane molecules, including VE-cadherin. In biochemical analyses, rigorous immunoprecipitation experiments have revealed N-cadherin, desmoplakin, desmoglein-2, plakophilin-2, plakoglobin and plectin as very stably bound complex partners. We conclude that myozap is a general component of cell-cell junctions not only in the myocardium but also in diverse endothelia of the blood and lymph vascular systems of adult mammals, suggesting that this protein not only serves a specific role in the heart but also a broader set of functions in the vessel systems. We also propose to use myozap as an endothelial cell type marker in diagnoses.

Lymphangiogenesis in post-natal tissue remodeling: lymphatic endothelial cell connection with its environment

The main physiological function of the lymphatic vasculature is to maintain tissue fluid homeostasis. Lymphangiogenesis or de novo lymphatic formation is closely associated with tissue inflammation in adults (i.e. wound healing, allograft rejection, tumor metastasis). Until recently, research on lymphangiogenesis focused mainly on growth factor/growth factor-receptor pathways governing this process. One of the lymphatic vessel features is the incomplete or absence of basement membrane. This close association of endothelial cells with the underlying interstitial matrix suggests that cell-matrix interactions play an important role in lymphangiogenesis and lymphatic functions. However, the exploration of interaction between extracellular matrix (ECM) components and lymphatic endothelial cells is in its infancy. Herein, we describe ECM-cell and cell-cell interactions on lymphatic system function and their modification occurring in pathologies including cancer metastasis.

Quantitative analysis of lymph vessel characteristics in organ confined prostate cancer

BACKGROUND

The objective of this study was to analyze the characteristics of lymphatic vasculature in normal and (peri)tumoral prostate tissue, applying accurate and objective quantification techniques based on digital image analysis.

METHODS

Radical prostatectomy specimens of 27 patients were selected containing organ confined peripheral zone tumors, which were restricted to one side of the prostate (pT2a). Lymph vessels were visualized by immunohistochemistry against D2-40. Lymphatic vessel density, perimeter, and area were assessed over the entire tumor and corresponding contralateral normal tissue. Also, morphology (area, perimeter, and diameter) of individual lymph vessels were measured in (peri)tumoral and normal tissue.

RESULTS

No differences were found in the overall lymph vasculature between tumor and normal peripheral zone. However, the area, perimeter, and diameter of individual lymph vessel profiles were significantly decreased in (peri)tumoral as compared to normal tissue. No differences were seen for these parameters between peritumoral and tumoral area. Comparing the coefficient of variation between compartments (normal, (peri)tumoral), no differences were observed for any parameter.

CONCLUSIONS

Although differences exist between the morphology of individual lymph vessels in tumor versus normal tissue, the overall vascular bed (number and summed area and perimeter of lymphatics per area unit tissue) is unaffected in tumor. Peritumoral lymphatics resemble lymphatics in tumor tissue rather than normal lymphatics.

Desmosomal molecules in and out of adhering junctions: normal and diseased States of epidermal, cardiac and mesenchymally derived cells

Current cell biology textbooks mention only two kinds of cell-to-cell adhering junctions coated with the cytoplasmic plaques: the desmosomes (maculae adhaerentes), anchoring intermediate-sized filaments (IFs), and the actin microfilament-anchoring adherens junctions (AJs), including both punctate (puncta adhaerentia) and elongate (fasciae adhaerentes) structures. In addition, however, a series of other junction types has been identified and characterized which contain desmosomal molecules but do not fit the definition of desmosomes. Of these special cell-cell junctions containing desmosomal glycoproteins or proteins we review the composite junctions (areae compositae) connecting the cardiomyocytes of mature mammalian hearts and their importance in relation to human arrhythmogenic cardiomyopathies. We also emphasize the various plakophilin-2-positive plaques in AJs (coniunctiones adhaerentes) connecting proliferatively active mesenchymally-derived cells, including interstitial cells of the heart and several soft tissue tumor cell types. Moreover, desmoplakin has also been recognized as a constituent of the plaques of the complexus adhaerentes connecting certain lymphatic endothelial cells. Finally, we emphasize the occurrence of the desmosomal transmembrane glycoprotein, desmoglein Dsg2, out of the context of any junction as dispersed cell surface molecules in certain types of melanoma cells and melanocytes. This broadening of our knowledge on the diversity of AJ structures indicates that it may still be too premature to close the textbook chapters on cell-cell junctions.

The junctions that don't fit the scheme: special symmetrical cell-cell junctions of their own kind

Immunocytochemical, electron-, and immunoelectron-microscopical studies have revealed that, in addition to the four major "textbook categories" of cell-cell junctions (gap junctions, tight junctions, adherens junctions, and desmosomes), a broad range of other junctions exists, such as the tiny puncta adhaerentia minima, the taproot junctions (manubria adhaerentia), the plakophilin-2-containing adherens junctions of mesenchymal or mesenchymally derived cell types including malignantly transformed cells, the composite junctions (areae compositae) of the mature mammalian myocardium, the cortex adhaerens of the eye lens, the interdesmosomal "sandwich" or "stud" junctions in the subapical layers of stratified epithelia and the tumors derived therefrom, and the complexus adhaerentes of the endothelial and virgultar cells of the lymph node sinus. On the basis of their sizes and shapes, other morphological criteria, and their specific molecular ensembles, these junctions and the genes that encode them cannot be subsumed under one of the major categories mentioned above but represent special structures in their own right, appear to serve special functions, and can give rise to specific pathological disorders.

Histopathological predictor for regional lymph node metastasis in gastric cancer

Regional lymph node metastasis in gastric cancer is a definitive indicator of the patient's prognosis. The goal of this study was to identify the predictors for lymph node metastasis among all the possible histopathological parameters, especially by conducting an objective discrimination of the lymphatic and blood vessels. A total of 210 resected primary gastric cancers with or without lymph node metastasis were evaluated based on the conventional histopathological parameters together with immunohistochemistry using antisera-recognizing lymphatic endothelial hyaluronan receptor-1 (LYVE-1), von Willebrand factor, and lymphangiogenesis promoter vascular endothelial growth factor-C (VEGF-C) antibodies. A multivariate regression analyses of the results indicated that only lymphatic invasion was a significant independent predictor of lymph node metastasis at any stage of cancer invasion. VEGF-C expression was partially related to lymph node metastasis in early gastric cancer. The identification of lymphatic invasion by LYVE-1 antibody is therefore useful to predict regional lymph node metastasis in gastric cancer.

Endothelial and virgultar cell formations in the mammalian lymph node sinus: endothelial differentiation morphotypes characterized by a special kind of junction (complexus adhaerens)

The lymph node sinus are channel structures of unquestionable importance in immunology and pathology, specifically in the filtering of the lymph, the transport and processing of antigens, the adhesion and migration of immune cells, and the spread of metastatic cancer cells. Our knowledge of the cell and molecular biology of the sinus-forming cells is still limited, and the origin and biological nature of these cells have long been a matter of debate. Here, we review the relevant literature and present our own experimental results, in particular concerning molecular markers of intercellular junctions and cell differentiation. We show that both the monolayer cells lining the sinus walls and the intraluminal virgultar cell meshwork are indeed different morphotypes of the same basic endothelial cell character, as demonstrated by the presence of a distinct spectrum of general and lymphatic endothelial markers, and we therefore refer to these cells as sinus endothelial/virgultar cells (SEVCs). These cells are connected by unique adhering junctions, termed complexus adhaerentes, characterized by the transmembrane glycoprotein VE-cadherin, combined with the desmosomal plaque protein desmoplakin, several adherens junction plaque proteins including alpha- and beta-catenin and p120 catenin, and components of the tight junction ensemble, specifically claudin-5 and JAM-A, and the plaque protein ZO-1. We show that complexus adhaerentes are involved in the tight three-dimensional integration of the virgultar network of SEVC processes along extracellular guidance structures composed of paracrystalline collagen bundle "stays". Overall, the SEVC system might be considered as a local and specific modification of the general lymphatic vasculature system. Finally, physiological and pathological alterations of the SEVC system will be presented, and the possible value of the molecular markers described in histological diagnoses of autochthonous lymph node tumors will be discussed.

Protein p0071, a major plaque protein of non-desmosomal adhering junctions, is a selective cell-type marker

Protein p0071, which originally was introduced as a member of the p120-subfamily of armadillo proteins, common to desmosomes and adhaerens junctions (AJs) and to several other cell structures (centrosomes, midbodies), has been localized by using a series of novel mono- and polyclonal antibodies generated against various domains of the molecule. By protein analysis and immunolocalization techniques, protein p0071 has been localized as a plaque protein in AJs of diverse epithelia and certain vascular endothelia, in the composite junctions (areal compositae) of the intercalated disks of cardiomyocytes, and in the punctate or more extended AJs of the vast majority of cell culture types examined, including mitotic states. Using these antibodies, we have also shown that this AJ protein occurs only rarely or is even absent in tissues such as skeletal and smooth muscles, in a series of mesenchymal tissue cells, and in specific desmosome-rich cells such as those of the upper layers of the epidermis and certain other stratified epithelia and Hassall corpuscles of the thymus. We have also demonstrated that p0071 is absent from desmosomes. The occurrence of two major subtypes of lymphatic endothelial cells, one with AJs containing p0071 and one without detectable p0071, is emphasized. Possible structural and functional roles of p0071 are discussed in light of these new findings regarding its localization, and the addition of p0071 to the armamentarium of cytodiagnostic cell-type markers is recommended.

Organization and developmental aspects of lymphatic vessels

The lymphatic system plays important roles in maintaining tissue fluid homeostasis, immune surveillance of the body, and the taking up dietary fat and fat-soluble vitamins A, D, E and K. The lymphatic system is involved in many pathological conditions, including lymphedema, inflammatory diseases, and tumor dissemination. A clear understanding of the organization of the lymphatic vessels in normal conditions would be critically important to develop new treatments for diseases involving the lymphatic vascular system. Therefore, the present paper reviews the organization of the lymphatic vascular system of a variety of organs, including the thyroid gland, lung and pleura, small intestine, cecum and colon in the rat, the diaphragm in the rat, monkey, and human, Peyer's patches and the appendix in the rabbit, and human tonsils. Methods employed include scanning electron microscopy of lymphatic corrosion casts and tissues with or without treatment of alkali maceration technique, transmission electron microscopy of intact tissues, confocal microscopy in conjunction with immunohistochemistry to some lymphatic-specific markers (i.e., LYVE-1 and VEGFR-3), and light microscopy in conjunction with enzyme-histochemistry to 5'-nucleotidase. Some developmental aspects of the lymphatic vessels and lymphedema are also discussed.

Lymph circulation in the liver

The liver produces a large amount of lymph, which is estimated to be 25 to 50 % of lymph flowing through the thoracic duct. The hepatic lymphatic system falls into three categories depending on their locations: portal, sublobular, and superficial lymphatic vessels. It is suggested that 80 % or more of hepatic lymph drains into portal lymphatic vessels, while the remainder drains through sublobular and capsular lymphatic vessels. The hepatic lymph primarily comes from the hepatic sinusoids. Our tracer studies, together with electron microscopy, show many channels with collagen fibers traversing through the limiting plate and connecting the space of Disse with the interstitial space either in the portal tracts, or around the sublobular veins. Fluid filtered out of the sinusoids into the space of Disse flows through the channels traversing the limiting plate either independently of blood vessels or along blood vessels and enters the interstitial space of either portal tract or sublobular veins. Fluid in the space of Disse also flows through similar channels traversing the hepatocytes intervening between the space of Disse and the hepatic capsule and drains into the interstitial space of the capsule. Fluid and migrating cells in the interstitial space pass through prelymphatic vessels to finally enter the lymphatic vessels. The area of the portal lymphatic vessels increases in liver fibrosis and cirrhosis and in idiopathic portal hypertension. Lymphatic vessels are abundant in the immediate vicinity of the hepatocellular carcinoma (HCC) and liver metastasis. HCCs expressing vascular endothelial growth factor-C are more liable to metastasize, indicating that lymphangiogenesis is associated with their enhanced metastasis.

The role of the lymphatic circulation in the natural history and expression of cardiovascular disease

The lymphatic vasculature is essential to fluid, protein and cellular transport, and to immune responsiveness. The last decade has witnessed a virtual renaissance of investigation into the function of the lymphatic microvasculature, prompting re-consideration of its role in the genesis and progression of cardiovascular pathology. The lymphatic microvasculature of the heart and vascular wall likely participate in atherogenesis, myocardial infarction, congestive heart failure, and cardiac transplantation. Intensive exploration of lymphatic mechanisms of cardiovascular disease is likely to lead to enhanced insights and novel therapeutic approaches.

Emilin1 deficiency causes structural and functional defects of lymphatic vasculature

Lymphatic-vasculature function critically depends on extracellular matrix (ECM) and on its connections with lymphatic endothelial cells (LECs). However, the composition and the architecture of ECM have not been fully taken into consideration in studying the biology and the pathology of the lymphatic system. EMILIN1, an elastic microfibril-associated protein, is highly expressed by LECs in vitro and colocalizes with lymphatic vessels in several mouse tissues. A comparative study between WT and Emilin1-/- mice highlighted the fact that Emilin1 deficiency in both CD1 and C57BL/6 backgrounds results in hyperplasia, enlargement, and frequently an irregular pattern of superficial and visceral lymphatic vessels and in a significant reduction of anchoring filaments. Emilin1-deficient mice also develop larger lymphangiomas than WT mice. Lymphatic vascular morphological alterations are accompanied by functional defects, such as mild lymphedema, a highly significant drop in lymph drainage, and enhanced lymph leakage. Our findings demonstrate that EMILIN1 is involved in the regulation of the growth and in the maintenance of the integrity of lymphatic vessels, a fundamental requirement for efficient function. The phenotype displayed by Emilin1(-/-) mice is the first abnormal lymphatic phenotype associated with the deficiency of an ECM protein and identifies EMILIN1 as a novel local regulator of lymphangiogenesis.

Lymph vascular invasion in invasive mammary carcinomas identified by the endothelial lymphatic marker D2-40 is associated with other indicators of poor prognosis

Background

Immunohistochemical studies of lymphatic vessels have been limited by a lack of specific markers. Recently, the novel D2-40 antibody, which selectively marks endothelium of lymphatic vessels, was released. The aim of our study is to compare lymphatic and blood vessel invasion detected by hematoxylin and eosin (H&E) versus that detected by immunohistochemistry, relating them with morphologic and molecular prognostic factors.

Methods

We selected 123 cases of invasive mammary carcinomas stratified into three subgroups according to axillary lymph node status: macrometastases, micrometastases, and lymph node negative. Lymphatic (LVI) and blood (BVI) vessel invasion were evaluated by H&E and immunohistochemistry using the D2-40 and CD31 antibodies, and related to histologic tumor type and grade, estrogen and progesterone receptors, E-cadherin, Ki67, p53, and Her2/neu expression.

Results

LVI was detected in H&E-stained sections in 17/123 cases (13.8%), and in D2-40 sections in 35/123 cases (28.5%) (Kappa = 0.433). BVI was detected in H&E-stained sections in 5/123 cases (4.1%), and in CD31 stained sections in 19/123 cases (15.4%) (Kappa = 0.198). LVI is positively related to higher histologic grade (p = 0.013), higher Ki67 expression (p = 0.00013), and to the presence of macrometastases (p = 0.002), and inversely related to estrogen (p = 0.0016) and progesterone (p = 0.00017) receptors expression.

Conclusion

D2-40 is a reliable marker of lymphatic vessels and is a useful tool for lymphatic emboli identification in immunostained sections of breast carcinomas with higher identification rates than H&E. Lymphatic vessel invasion was related to other features (high combined histologic grade, high Ki67 score, negative hormone receptors expression) associated with worse prognosis, probable reflecting a potential for lymphatic metastatic spread and aggressive behavior.

Impact of immunohistochemically identified lymphatic invasion on nodal metastasis in early gastric cancer

BACKGROUND

Among various clinical and pathological findings, lymphatic invasion (Ly) is the strongest risk factor for nodal metastasis in gastric cancer. However, the diagnosis of Ly is subjective and often inaccurate because of the difficulty of detecting lymphatic vessels with conventional hematoxylin and eosin (HE) staining.

METHODS

The distribution of lymphatics in the normal gastric wall was immunohistochemically characterized using a new selective marker of lymphatic endothelium, D2-40, in surgical specimens resected for early gastric cancer (EGC). Then, Ly in the primary lesion was reevaluated, and the positive (PPV) and negative (NPV) predictive values for nodal metastasis were comparatively examined for Ly detected by HE staining (Ly-HE) and by immunohistochemical staining (Ly-IM) in 131 cases of EGC.

RESULTS

D2-40-positive lymphatic vessels were observed in the deep proper mucosal layer, and the lymphatic vessel density (LVD) was extremely high in the muscularis mucosa (MM) layer. The number of Ly-IM-positive cases (15/131) was higher than the Ly-HE-positive cases (10/131). In 48 cases of intestinal-type cancer, Ly-IM had a PPV of 33.3% (2/6) and anNPV of 100% (42/42), which was more accurate than the corresponding figures for Ly-HE (25% and 98%, respectively). In contrast, the accuracy of Ly-IM was similar to that of Ly-HE in 83 cases of diffuse-type cancer.

CONCLUSION

Lymphatic vessels are most densely distributed in the MM layer in the gastric wall. Immunohistochemical identification of lymphatics is useful to increase the accuracy of diagnosing Ly in resected gastric EGCs. Ly-IM is superior to Ly-HE as a predictor of nodal metastasis, at least for intestinal-type EGC.

First international consensus on the methodology of lymphangiogenesis quantification in solid human tumours

The lymphatic system is the primary pathway of metastasis for most human cancers. Recent research efforts in studying lymphangiogenesis have suggested the existence of a relationship between lymphatic vessel density and patient survival. However, current methodology of lymphangiogenesis quantification is still characterised by high intra- and interobserver variability. For the amount of lymphatic vessels in a tumour to be a clinically useful parameter, a reliable quantification technique needs to be developed. With this consensus report, we therefore would like to initiate discussion on the standardisation of the immunohistochemical method for lymphangiogenesis assessment.

Accurate assessment of lymph vessel tumor emboli in invasive ductal carcinoma of the breast according to tumor areas, and their prognostic significance

Lymph vessel tumor emboli (LVTEs) within tumors are difficult to distinguish from stroma-invasive tumor foci. The purpose of this study was to evaluate staining of LVTEs with hematoxylin-eosin (HE) and with D2-40 to determine whether LVTEs identified by HE staining alone are D2-40-positive LVTE and whether the presence of LVTE identified by HE or D2-40 staining is an accurate predictor of outcome in 151 patients with invasive ductal carcinoma (IDC) of the breast. We first attempted to identify LVTE in the stroma-invasive tumor area (intratumor area), the advance area, and the nontumor area by HE staining alone, and then LVTE identified by HE staining was confirmed by D2-40 staining. The number of LVTE identified by HE staining and D2-40 staining successively increased from the intratumor area to the nontumor area. Although D2-40 staining detected larger numbers of LVTE than HE staining in all tumor areas, the highest positive predictive value of LVTE was observed in the intratumor area, and the next was in the advance area, and then the nontumor area, and significant correlations were found between the numbers of LVTE stained by HE and D2-40 in the same tumor areas. LVTE identified by HE staining or D2-40 staining in the intratumor area or nontumor area significantly increased the risk for tumor recurrence or death of patients with IDC, independent of hormone receptor status or nodal status. The results of this study demonstrate that the existence of intratumoral LVTE and that the presence of intratumoral LVTE identified by HE staining or D2-40 staining are accurate predictors of the outcome of patients with IDC of the breast.

New Insights into the Molecular Control of the Lymphatic Vascular System and its Role in Disease

The cutaneous lymphatic system plays an important role in the maintenance of tissue fluid homeostasis, in the afferent phase of the immune response, and in the metastatic spread of skin cancers. However, the lymphatic system has not received as much scientific attention as the blood vascular system, largely due to a lack of lymphatic-specific markers and to the dearth of knowledge about the molecular regulation of its development and function. The recent identification of genes that specifically control lymphatic development and the growth of lymphatic vessels (lymphangiogenesis), together with the discovery of new lymphatic endothelium-specific markers, have now provided new insights into the molecular mechanisms that control lymphatic growth and function. Moreover, studies of several genetic mouse models have set the framework for a new molecular model for embryonic lymphatic vascular development, and have identified molecular pathways whose mutational inactivation leads to human diseases associated with lymphedema. These scientific advances have also provided surprising evidence that malignant tumors can directly promote lymphangiogenesis and lymphatic metastasis, and that lymphatic vessels play a major role in cutaneous inflammation and in the cutaneous response to UVB irradiation.

Lymphangiogenesis in the bone-implant interface of orthopedic implants: importance and consequence

The lymphatic system plays an essential physiological role in homeostasis, interstitial fluid composition, and immunity while impaired lymphatic function has been implicated in a number of pathological conditions, including arthritis and delayed wound healing. This study investigated lymphatic capillary growth and lymphangiogenesis pathways in the bone-implant interface from patients with aseptically loosened prosthetic joints. The newly developed lymphatic specific marker, podoplanin, has enabled the first demonstration of lymphatic capillaries in peri-prosthetic tissues (60% of cases contained podoplanin positive vessels). The pro-lymphangiogenic factor (VEGF-C) and its receptor VEGFR-3 showed high level of expression in these tissues, (often in areas of high levels of wear debris). However despite the upregulation of the lymphangiogenesis pathway by a VEGF-C/VEGFR-3-mediated mechanism, there were relatively few podoplanin positive lymphatic vessels in the bone-implant interface (3.4% of total vessels). This may have important pathological consequences in terms of perpetuating inflammation and edema by inhibiting the removal of macromolecules, cells, and interstitial fluid. The identification of lymphatic vessels with internalized polyethylene wear particles provides evidence of this route of wear debris transportation to distal sites. This paper highlights the importance of lymphatic vessels in the maintenance of local and distal inflammatory responses to prosthetic wear particles.

On the transendothelial passage of tumor cell from extravasal matrix into the lumen of absorbing lymphatic vessel

The aim of the research is the study of ultrastructural characteristics of the absorbing lymphatic vessel and of tumor cell passage through the endothelial lymphatic wall in (a) subcutaneous xenografts of T84 colon adenocarcinoma and B16 melanoma cell lines in nude mice and (b) human colorectal cancer. It was found that the tumor-associated absorbing lymphatic (TAAL) vessel has the same ultrastructural characteristics as the absorbing lymphatic vessel in normal organs, and it is provided with an endothelial wall wholly lacking a continuous basement membrane, pores, fenestrations, and open junctions. The TAAL vessel is always missing in the studied tumor masses as far as the central stroma is concerned, whereas it is always present in the peripheral area of the tumor and in the peritumoral connective tissue. The factors of extravasal matrix that play an active role in migration process of invasive phenotype tumor (IPT) cell after its detachment from tumor mass, as well as the role of cytoplasmic protrusions (pseudopod-like) in lymphatic recognition, were considered. For the first time, this study demonstrated the transendothelial passage of IPT cell inside the TAAL vessel lumen, which takes place by means of the intraendothelial channel (approximately 1.8-2.1 mum in diameter and 6.8-7.2 microm in length). This channel is to be considered a transient morphological entity organized by TAAL vessel endothelium by means of still unidentified molecular mechanisms. Therefore, it appears to be ascertained that the intraendothelial channel represents a step forward in the knowledge of the drainage into lymphatic circulation of interstitial fluid and the answer to the lack of knowledge expressed till today by researchers concerning the modality of passage of the tumor cell through the endothelial wall of the TAAL vessel.

The area composita of adhering junctions connecting heart muscle cells of vertebrates. II. Colocalizations of desmosomal and fascia adhaerens molecules in the intercalated disk

Using immunofluorescence histochemistry and immunoelectron microscopy on sections through myocardiac tissues of diverse mammalian (human, cow, rat, mouse) and fish species we show that both desmosomal and fascia adhaerens proteins identified by gel electrophoresis and immunoblot occur in the area composita, the by far major type of plaque-bearing junctions of the intercalated disks (IDs) connecting cardiomyocytes. Specifically, we demonstrate that desmoplakin and the other desmosomal proteins occur in these junctions, together with N-cadherin, cadherin-11, alpha- and beta-catenin as well as vinculin, afadin and proteins p120(ctn), ARVCF, p0071, and ZO-1, suggestive of colocalization. We conclude that the predominant type of adhering junction present in IDs is a junction sui generis, termed area composita, that is characterized by an unusually high molecular complexity and an intimate association of molecules of both ensembles, the desmosomal one and the fascia adhaerens category. We discuss possible myocardium-specific, complex-forming interactions between members of the two ensembles and the relevance of our findings for the formation and functioning of the heart and for the understanding of hereditary and other cardiomyopathies. We further propose to use this highly characteristic area composita ensemble of molecules as cardiomyocyte markers for the monitoring of cardiomyogenesis, cardiomyocyte regeneration and possible cardiomyocyte differentiation from mesenchymal stem cells.

The complexus adhaerens of mammalian lymphatic endothelia revisited: a junction even more complex than hitherto thought

The significance of a special kind of VE-cadherin-based, desmoplakin- and plakoglobin-containing adhering junction, originally identified in certain endothelial cells of the mammalian lymphatic system (notably the retothelial cells of the lymph node sinus and a subtype of lining endothelial cells of peripheral lymphatic vessels), has been widely confirmed and its importance in the formation of blood and lymph vessels has been demonstrated in vivo and in vitro. We have recently extended the molecular and structural characterization of the complexus adhaerens and can now report that it represents a rare and special combination of components known from three other major types of cell junction. It comprises zonula adhaerens proteins (VE-cadherin, alpha- and beta-catenin, protein p120(ctn), and afadin), desmosomal plaque components (desmoplakin and plakoglobin), and tight-junction proteins (claudin-5 and ZO-1) and forms junctions that vary markedly in size and shape. The special character and the possible biological roles of the complexus adhaerens and its unique ensemble of molecules in angiogenesis, immunology, and oncology are discussed. The surprising finding of claudin-5 and protein ZO-1 in substructures of retothelial cell-cell bridges, i.e. structures that do not separate different tissues or cell layer compartments, suggests that such tight-junction molecules are involved in functions other than the "fence" and "barrier" roles of zonulae occludentes.

Topographic distribution of lymphatic vessels in the normal human prostate

BACKGROUND

The lymphatic endothelial hyaluronan receptor (LYVE-1) is a specific cell surface protein in lymphatic endothelium. The antiserum against human LYVE-1 was developed and was confirmed a powerful marker of lymphatic endothelium in human organs. With this novel marker we investigated the small network of intraprostate lymphatic vessels.

METHODS

To identify intraprostatic lymphatic vessels, we performed an immunohistochemical staining method using LYVE-1 pAb and von Willebrand Factor (vWF), and assessed the difference in distribution of small lymphatic vessels between the components in the prostate.

RESULTS

The density of lymphatic vessel was significantly high around ejaculatory ducts and in the fibromascular area between the globular area of peripheral zone and transitional zone. Predominat lymphatic vessels distributed in the fibromascular area in the anterior and posterior prostate of extrastromal area.

CONCLUSIONS

Recognition of the distinctive features of the intraprostate lymphatic network, can help the investigation of lymphatic involvement in cancer of the prostate.

Influences of angiogenesis and lymphangiogenesis on cancerous invasion in experimentally induced tongue carcinoma

BACKGROUND

Although it is clear that dissemination via the blood system involves angiogenesis, it is uncertain whether tumors also induce lymphangiogenesis or simply invade existing peritumoral vessels. The purpose of this study was to elucidate changes in tumor blood and lymph vessels in cases involving the invasion of squamous cell carcinoma in the oral cavity, and its significance. Blood and lymph vessels densities in tongue carcinomas induced in hamsters were investigated.

METHODS

Tongue cancer was induced by abrading the right margin of the tongue of each hamster with an endodontic barbed broach and subsequently applying 1.0% 9,10-dimenthl-1,2-benzanthracene (DMBA) dissolved in acetone, three times a week, at the same site. Fresh frozen sections were prepared and blood vessels stained blue by perfusion with Coomassie Brilliant Blue and lymph vessels stained brown for 5'-nucleotidase. The effects on the blood vessels and lymph vessels were observed.

RESULTS

The results showed that blood and lymph vessel densities were greater in the advanced carcinoma tissues than in normal tissue. These were compared in terms of the mode of cancer invasion. As tumor invasion progressed, the blood vessel density decreased but lymph vessel density tended to be higher in high-degree tumor invasion than in low-degree tumor invasion. The expression of vascular endothelial growth factor-C was seen more frequently as tumor invasion progressed.

CONCLUSIONS

The present findings indicated that angiogenesis and lymphangiogenesis are affected by cancerous invasion.

Angiogenic and lymphangiogenic microvessel density in breast carcinoma: correlation with clinicopathologic parameters and VEGF-family gene expression

Angiogenesis and lymphangiogenesis are essential for breast cancer progression and are regulated by vascular endothelial growth factors (VEGF). To determine clinical and molecular correlates of these processes, we measured blood and lymphatic vascular microvessel density in 29 invasive carcinomas (22 ductal, six lobular, one papillary), using the vascular marker CD31 and the novel lymphatic marker D2-40. Microvessel density was assessed microscopically and by image cytometry, and was compared with tumor histology, grade, stage, lymph node metastasis, hormone receptors, HER2/neu status, and expression of VEGF, VEGF-C and VEGF-D by immunohistochemistry or quantitative RT-PCR. Strong correlation was observed between visual and image cytometric microvessel density using D2-40 but not CD31 (P=0.016 and 0.1521, respectively). Image cytometric CD31 microvessel density correlated with tumor size, grade, stage and lymph node metastasis (P=0.0001, 0.0107, 0.0035 and 0.0395, respectively). D2-40 microvessel density correlated with tumor stage (P=0.0123 by image cytometry) and lymph node metastasis (P=0.0558 by microscopy). Immunohistochemical VEGF signal in peritumoral blood vessels correlated with image cytometric CD31 and D2-40 microvessel density (P=0.022 and 0.0012, respectively), consistent with the role of VEGF in blood and lymphatic vascular growth. Intratumoral VEGF-C and VEGF-D expression by quantitative RT-PCR correlated with D2-40 (P=0.0291 by image cytometry) but not with CD31 microvessel density, which could suggest a selective role of VEGF-C and VEGF-D in lymphangiogenesis. CD31 and D2-40 microvessel density correlated significantly with several prognostic factors, including lymph node metastasis. Thus, measurements of angiogenesis and lymphangiogenesis may have utility for breast cancer pathology, particularly for estimation of metastatic risk.

Transendothelial transport and migration in vessels of the apparatus lymphaticus periphericus absorbens (ALPA)

The vessel of the apparatus lymphaticus periphericus absorbens (ALPA) represents the sector with high absorption capacity of the canalization of the lymphatic vascular system. It plays a basic role in preserving tissue homeostasis and in directing interstitial capillary filtrate back to the bloodstream. ALPA lymphatic endothelium differs from the endothelia of conduction and flowing vessels (precollectors, prelymph nodal and postlymph nodal collectors, main trunks), since it presents a discontinuous basement membrane, which is often absent, and lacks pores and fenestrations. The mesenchymal origin of the ALPA lymphatic vessel, morphological and ultrastructural aspects, intrinsic contractile properties, the presence of valves, innervation, and specific lymphatic markers that reliably distinguish it from blood capillaries are studied. Furthermore, its role in lymph formation through different mechanisms (hydrostatic pressure and colloidal osmotic-reticular mechanisms, vesicular pathway, and intraendothelial channel) is investigated. We have studied morphological and biomolecular mechanisms that control the transendothelial migration, from the extracellular interstitial matrix into the lumen of the lymphatic vessel, of cells involved in immune response and resistance (lymphocyte recirculation, etc.) and in the tumoral metastatic process via the lymphatic system. Finally, future research prospects, clinical implications, and therapeutic strategies are considered.

Desmoplakin and Plakoglobin - Specific Markers of Lymphatic Vessels in the Skin?

Monoclonal antibodies against Desmoplakin and Plakoglobin were tested for their suitability as specific markers of lymphatic vessels. The tissue samples were taken from horse skin in an attempt to establish the horse as a model for human lymphatic diseases. To obtain a clear, positive identification of blood and lymphatic vessels, immunohistochemical staining with antibodies against vascular endothelial growth factor receptor 3 (VEGFR-3) and platelet endothelial adhesion molecule (PECAM-1, CD31), was compared with Desmoplakin and Plakoglobin. Because anti-VEGFR-3 is specific for lymphatic vessels in the skin while anti-CD31 stains blood and lymphatic vessels as well, it can be concluded that VEGFR-3(-)/CD31(+) vessels are blood vessels and VEGFR-3(+)/CD31(+) vessels are lymphatic vessels. It was documented on serial sections that Plakoglobin stains both blood and lymphatic vessels. However, Desmoplakin did not stain several positively identified lymphatic vessels. Therefore, Desmoplakin and Plakoglobin antibodies are not specific markers of lymphatic vessels in the skin and the staining pattern is tissues and species dependent.

Lymphatics at the crossroads of angiogenesis and lymphangiogenesis

The lymphatic system is implicated in interstitial fluid balance regulation, immune cell trafficking, oedema and cancer metastasis. However, the sequence of events that initiate and coordinate lymphatic vessel development (lymphangiogenesis) remains obscure. In effect, the understanding of physiological regulation of lymphatic vasculature has been overshadowed by the greater emphasis focused on angiogenesis, and delayed by a lack of specific markers, thereby limiting this field to no more than a descriptive characterization. Recently, new insights into lymphangiogenesis research have been due to the discovery of lymphatic-specific markers and growth factors of vascular endothelial growth factor (VEGF) family, such as VEGF-C and VEGF-D. Studies using transgenic mice overexpressing VEGF-C and VEGF-D have demonstrated a crucial role for these factors in tumour lymphangiogenesis. Knowledge of lymphatic development has now been redefined at the molecular level, providing an interesting target for innovative therapies. This review highlights the recent insights and advances into the field of lymphatic vascular research, outlining the most important aspects of the embryo development, structure, specific markers and methods applied for studying lymphangiogenesis. Finally, molecular mechanisms involved in the regulation of lymphangiogenesis are described.

New insights into the biology and pathology of the cutaneous lymphatic system

The cutaneous lymphatic system plays an important role in the maintenance of tissue fluid homeostasis, in the afferent phase of the immune response, and in the metastatic spread of skin cancers. The recent identification of genes that specifically control lymphatic development and the growth of lymphatic vessels (lymphangiogenesis), together with the discovery of new lymphatic endothelium-specific markers have now provided new insights into the molecular mechanisms that control lymphatic development and function. These scientific advances have also led to a new understanding of the genetic basis of several hereditary diseases that are associated with lymphedema, and they have provided surprising evidence that malignant tumors can directly promote lymphangiogenesis and lymphatic metastasis.

Cyclooxygenase-2 induces EP1- and HER-2/Neu-dependent vascular endothelial growth factor-C up-regulation: a novel mechanism of lymphangiogenesis in lung adenocarcinoma

Cyclooxygenase (COX)-2, the inducible isoform of prostaglandin H synthase, has been implicated in the progression of human lung adenocarcinoma. However, the mechanism underlying COX-2's effect on tumor progression remains largely unknown. Lymphangiogenesis, the formation of new lymphatic vessels, has recently received considerable attention and become a new frontier of tumor metastasis research. Here, we study the interaction between COX-2 and the lymphangiogenic factor, vascular endothelial growth factor (VEGF)-C, in human lung cancer cells and their implication in patient outcomes. We developed an isopropyl-beta-D-thiogalactopyranoside-inducible COX-2 gene expression system in human lung adenocarcinoma CL1.0 cells. We found that VEGF-C gene expression but not VEGF-D was significantly elevated in cells overexpressing COX-2. COX-2-mediated VEGF-C up-regulation was commonly observed in a broad array of non-small cell lung cancer cell lines. The use of pharmacological inhibitors or activators and genetic inhibition by EP receptor-antisense oligonucleotides revealed that prostaglandin EP(1) receptor but not other prostaglandin receptors is involved in COX-2-mediated VEGF-C up-regulation. At the mechanistic level, we found that COX-2 expression or prostaglandin E(2) (PGE(2)) treatment could activate the HER-2/Neu tyrosine kinase receptor through the EP(1) receptor-dependent pathway and that this activation was essential for VEGF-C induction. The transactivation of HER-2/Neu by PGE(2) was inhibited by way of blocking the Src kinase signaling using the specific Src family inhibitor, PP1, or transfection with the mutant dominant negative src plasmid. Src kinase was involved in not only the HER-2/Neu transactivation but also the following VEGF-C up-regulation by PGE(2) treatment. In addition, immunohistochemical staining of 59 lung adenocarcinoma specimens showed that COX-2 level was highly correlated with VEGF-C, lymphatic vessels density, and other clinicopathological parameters. Taken together, our results provided evidence that COX-2 up-regulated VEGF-C and promotes lymphangiogenesis in human lung adenocarcinoma via the EP(1)/Src/HER-2/Neu signaling pathway.

Expression of cys–cys chemokine ligand 21 on human gingival lymphatic vessels

The cys-cys (C-C) chemokine ligand 21 is a member of the C-C chemokines that constitute a group of heparin-binding cytokines with a pattern of four or six conserved cysteines. The CCL21 is known to be expressed in secondary lymphoid tissues, however it has rarely been reported for the expression on peripheral lymphatic vessels in somatic tissue. Here we investigated the expression of CCL21 on lymphatic vessels identified by anti-desmoplakin in uninflamed and inflamed human gingiva. In uninflamed tissue the expression of CCL21 was detected on lymphatic vessels in gingiva. In uninflamed gingiva the expression of CCL21 was detected on all lymphatic capillaries of the mucosal connective tissue papillae. There were two types of collecting lymphatic vessels in the lamina propria mucosae expressing CCL21 strongly or very weakly. In inflamed gingiva no expression of CCL21 was detected on lymphatic vessels. In all tissue sections no blood vessels expressing CCL21 were observed. These results may suggest that the expression of CCL21 is predominantly induced in the peripheral lymphatic endothelium of the uninflamed mucosal microcirculation, and that under inflamed conditions a reduction of CCL21 occurs in lymphatic endothelium.

Expression of vascular endothelial growth factor C and chemokine receptor CCR7 in gastric carcinoma and their values in predicting lymph node metastasis

AIM: To study the expression of vascular endothelial growth factor C (VEGF-C) and chemokine receptor CCR7 in gastric carcinoma and to investigate their associations with lymph node metastasis of gastric carcinoma and their values in predicting lymph node metastasis.

METHODS: The expression of VEGF-C and CCR7 in gastric carcinoma tissues obtained from 118 patients who underwent curative gastrectomy was examined by immunohistochemistry. Among these patients, 39 patients underwent multi-slice spiral CT (MSCT) examination.

RESULTS: VEGF-C and CCR7 were positively expressed in 52.5 and 53.4% of patients. VEGF-C expression was more frequently found in tumors with lymph node metastasis than those without it (P < 0.001). VEGF-C expression was also closely related to lymphatic invasion (P < 0.001), vascular invasion (P < 0.01), and TNM stage (P < 0.001). However, there was no significant correlation between VEGF-C expression and age at surgery, gender, tumor size, tumor location, Lauren classification, and depth of invasion. CCR7 expression was significantly higher in patients with lymph node metastasis compared with those without lymph node metastasis (P < 0.001) and was also associated with tumor size (P < 0.01), depth of invasion (P < 0.001), lymphatic invasion (P < 0.001), and TNM stage (P < 0.001). However, the presence of CCR7 had no correlation to age at surgery, gender, tumor location, Lauren classification, and vascular invasion. Among the 39 patients who underwent MSCT examination, only CCR7 expression was related to lymph node metastasis determined by MSCT (P < 0.05). In the current retrospective study, the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of VEGF-C and CCR7 expression in the diagnosis of lymph node metastasis for patients with gastric carcinoma were 73.8%, 70.2%, 72.6%, 71.4% and 72.0%, and 82.0%, 77.2%, 79.4%, 80.0% and 79.7%, respectively. After subdivision according to the combination of VEGF-C and CCR7 expression, receiver operating characteristic (ROC) analysis showed that the accuracy of the combined examination of VEGF-C and CCR7 expression in predicting lymph node metastasis was relatively high (area under ROC curve [Az] = 0.83).

CONCLUSION: The expression of VEGF-C and CCR7 is related to lymph node metastasis of gastric carcinoma and both of them may become new targets for the treatment of gastric carcinoma. Furthermore, the combined examination of VEGF-C and CCR7 expression in endoscopic biopsy specimens may be useful in predicting lymph node metastasis of gastric carcinoma and deciding the extent of surgical lymph node resection.

Immunohistochemical detection of human small lymphatic vessels under normal and pathological conditions using the LYVE-1 antibody

The spread of tumor cells via lymphatic vessels to the lymph nodes is an important indicator of malignancy. However, previous markers used to identify lymphatic endothelium gave ambiguous results in immunohistochemical analyses with paraffin-embedded tissues. In this study, we attempted to prepare a polyclonal antibody against human lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) for detecting lymphatic vessels using immunohistochemistry. The antibody was raised against a region near the transmembrane anchor of LYVE-1 in New Zealand white rabbits. Immunostainings with anti-LYVE-1 and von Willebrand factor antibodies were performed in various normal and pathological tissues. LYVE-1 expression was confined to the endothelial surface of lymphatic vessels but was not found in the endothelium of blood vessels, which were positive for von Willebrand factor. Our LYVE-1 polyclonal antibody was useful for the identification of small lymphatic vessels in normal human tissues. In addition, the immunostaining enabled us to distinguish lymphatic invasion by malignant tumor cells from blood vessel invasion using paraffin-embedded sections. In conclusion, our polyclonal antibody against the transmembrane anchor of the peptide can be used to detect human lymphatic vessels under various conditions.

Lymphatic vasculature development

Although the process of blood vasculature formation has been well documented, little is known about lymphatic vasculature development, despite its importance in normal and pathological conditions. The lack of specific lymphatic markers has hampered progress in this field. However, the recent identification of genes that participate in the formation of the lymphatic vasculature denotes the beginning of a new era in which better diagnoses and therapeutic treatment(s) of lymphatic disorders could become a reachable goal.

Expression of Toll-like receptors 2 and 4 on human intestinal lymphatic vessels

The Toll-like receptor (TLR) is a part of the innate immune system sensing pathogen-associated molecular patterns (PAMPs). Recently, TLRs 2 and 4 have been demonstrated for the ligand engagements, which result in the induction of cytokines. Here we investigated the expression of TLRs 2 and 4 on lymphatic vessels producing cys-cys chemokine ligand 21 (CCL21) in the human small intestine. The specificity of antibodies to TLRs was tested on a human monocyte leukemia cell line, umbilical vein endothelial cells (HUVEC), and periodontal ligament fibroblasts (PDLF) with the examination for the TLR gene expression by the reverse transcription-polymerase chain reaction (RT-PCR), and lymphatic vessels were identified by antibodies for platelet-endothelial cell adhesion molecule-1 (PECAM-1) and desmoplakin. The expression of CCL21 was not clearly detected on collecting lymphatic vessels in the submucosa while it was generally observed on the central lacteals of villi and lymphatic capillaries in the lamina propria mucosae. The reaction of antibodies to TLRs 2 and 4 was also not clearly detected on collecting lymphatic vessels in the submucosa and central lacteals of villi, but generally observed on lymphatic capillaries expressing CCL21 in the lamina propria mucosae of tissue where the expression of CCL21 and TLRs was not clearly observed in blood vessels. These may suggest that the expression of CCL21, and TLRs 2 and 4 is predominantly induced in the peripheral lymphatic endothelium of the small intestinal microcirculation. The lymphatic endothelium may contribute to allow dendritic cells to home into secondary lymphoid tissue through the expression of TLRs, the ligand engagements of which result in the induction of chemokines.

Expression of vascular endothelial growth factor D is associated with lymph node metastasis in human colorectal carcinoma

OBJECTIVE

Expression of vascular endothelial growth factor (VEGF)-D by tumors is associated with metastasis to lymph nodes in mice. However, there are few reports concerning the clinical significance of VEGF-D protein in human carcinoma.

METHODS

After confirming production of VEGF-D by eight colorectal carcinoma cell lines, we investigated relationships between the expression of VEGF-D protein, lymph node metastasis and postoperative survival in 83 colorectal carcinoma patients. mRNA levels in cell lines were evaluated using the real-time reverse transcriptase-polymerase chain reaction, and protein was detected by Western blotting in cell lines and by immunohistochemistry in resected tissues using an antibody recognizing the processed form of the molecule.

RESULTS

Immunohistochemistry showed VEGF-D-positive staining in 26 of the 83 carcinomas (31%). There was a significant relationship between the presence of VEGF-D protein and the incidence of lymph node metastasis (p < 0.01). Multivariate logistic regression analysis revealed that VEGF-D protein expression was an independent factor affecting lymph node metastasis (p < 0.01). Nonetheless, the presence or absence of VEGF-D protein had no significant impact on the survival of the patients (p = 0.15).

CONCLUSION

These results suggest that the expression of VEGF-D protein could be useful in predicting the nodal status of colorectal carcinoma patients.

Molecular control of lymphangiogenesis

The lymphatic vasculature plays a critical role in the regulation of body fluid volume and immune function. Extensive research into the molecular mechanisms that control blood vessel growth has led to identification of molecules that also regulate development and growth of the lymphatic vessels. This is generating a great deal of interest in the molecular control of the lymphatics in the context of embryogenesis, lymphatic disorders and tumor metastasis. Studies in animal models carried out over the past three years have shown that the soluble protein growth factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, and their cognate receptor tyrosine kinase, VEGF receptor-3 (VEGFR-3), are critical regulators of lymphangiogenesis. Furthermore, disfunction of VEGFR-3 has recently been shown to cause lymphedema. The capacity to induce lymphangiogenesis by manipulation of the VEGF-C/VEGF-D/VEGFR-3 signaling pathway offers new opportunities to understand the function of the lymphatic system and to develop novel treatments for lymphatic disorders.

Lymphatic endothelial reprogramming of vascular endothelial cells by the Prox-1 homeobox transcription factor

Lymphatic vessels are essential for fluid homeostasis, immune surveillance and fat adsorption, and also serve as a major route for tumor metastasis in many types of cancer. We found that isolated human primary lymphatic and blood vascular endothelial cells (LECs and BECs, respectively) show interesting differences in gene expression relevant for their distinct functions in vivo. Although these phenotypes are stable in vitro and in vivo, overexpression of the homeobox transcription factor Prox-1 in the BECs was capable of inducing LEC-specific gene transcription in the BECs, and, surprisingly, Prox-1 suppressed the expression of approximately 40% of the BEC-specific genes. Prox-1 did not have global effects on the expression of LEC-specific genes in other cell types, except that it up-regulated cyclin E1 and E2 mRNAs and activated the cyclin e promoter in various cell types. These data suggest that Prox-1 acts as a cell proliferation inducer and a fate determination factor for the LECs. Furthermore, the data provide insights into the phenotypic diversity of endothelial cells and into the possibility of transcriptional reprogramming of differentiated endothelial cells.

The role of tumor lymphangiogenesis in metastatic spread

The high mortality rates associated with cancer can be attributed to the metastatic spread of tumor cells from the site of their origin. Tumor cells invade either the blood or lymphatic vessels to access the general circulation and then establish themselves in other tissues. Clinicopathological data suggest that the lymphatics are an initial route for the spread of solid tumors. Detection of sentinel lymph nodes by biopsy provides significant information for staging and designing therapeutic regimens. The role of angiogenesis in facilitating the growth of solid tumors has been well established, but the presence of lymphatic vessels and the relevance of lymphangiogenesis to tumor spread are less clear. Recently, the molecular pathway that signals for lymphangiogenesis and relatively specific markers for lymphatic endothelium have been described allowing analyses of tumor lymphangiogenesis to be performed in animal models. These studies demonstrate that tumor lymphangiogenesis is a major component of the metastatic process and implicate members of the VEGF family of growth factors as key mediators of lymphangiogenesis in both normal biology and tumors.

Quantitative studies on the movement of fluid and lymphocytes through periodontal tissue and into the draining lymph

Chronic lymph drainage techniques in sheep have been used to map the pathways and to quantify the fluid and cell traffic through periodontal tissues. The continuous collection of cervical and prescapular lymph has demonstrated that 65% of labelled protein tracer injected into the periodontal tissues could be found in lymph over a period of 7.5 hours. Nearly 90% of the total radioactivity could be accounted for between the lymph and the tissue site. When silk was impregnated with radiolabelled albumin and a tooth ligated, the kinetics of the subsequent appearance of the tracer in lymph emphasized the ease with which macromolecules surrounding the teeth gain access to the lymphatics, regional lymph nodes, and immune apparatus. Animals were primed with BCG and then tuberculin (delayed hypersensitivity) lesions were simultaneously induced in the skin, bowel, and periodontium. When T cells were labelled with radioisotopes and their migration from blood to lymph measured, the periodontal tissue traffic pattern was distinct from the traffic pattern through DTH in the skin and also distinct from the pattern through the small intestine. This indicates that the lymphocyte traffic through the inflamed periodontium has unique features. This tissue specificity was not apparent when lesions were induced with TNFalpha. The static assessment of lymphocyte subsets within the tissues was also assessed with immunohistochemistry.