Immunohistochemical differentiation between lymphatic vessels and blood vessels--use of anti-basement membrane antibodies and anti-factor VIII-related antigen

Blood pressure lowering enhances cerebrospinal fluid efflux to the systemic circulation primarily via the lymphatic vasculature

BACKGROUND

Inside the incompressible cranium, the volume of cerebrospinal fluid is directly linked to blood volume: a change in either will induce a compensatory change in the other. Vasodilatory lowering of blood pressure has been shown to result in an increase of intracranial pressure, which, in normal circumstances should return to equilibrium by increased fluid efflux. In this study, we investigated the effect of blood pressure lowering on fluorescent cerebrospinal fluid tracer absorption into the systemic blood circulation.

METHODS

Blood pressure lowering was performed by an i.v. administration of nitric oxide donor (sodium nitroprusside, 5 µg kg-1 min-1) or the Ca2+-channel blocker (nicardipine hydrochloride, 0.5 µg kg-1 min-1) for 10, and 15 to 40 min, respectively. The effect of blood pressure lowering on cerebrospinal fluid clearance was investigated by measuring the efflux of fluorescent tracers (40 kDa FITC-dextran, 45 kDa Texas Red-conjugated ovalbumin) into blood and deep cervical lymph nodes. The effect of nicardipine on cerebral hemodynamics was investigated by near-infrared spectroscopy. The distribution of cerebrospinal fluid tracers (40 kDa horse radish peroxidase,160 kDa nanogold-conjugated IgG) in exit pathways was also analyzed at an ultrastructural level using electron microscopy.

RESULTS

Nicardipine and sodium nitroprusside reduced blood pressure by 32.0 ± 19.6% and 24.0 ± 13.3%, while temporarily elevating intracranial pressure by 14.0 ± 7.0% and 18.2 ± 15.0%, respectively. Blood pressure lowering significantly increased tracer accumulation into dorsal dura, deep cervical lymph nodes and systemic circulation, but reduced perivascular inflow along penetrating arteries in the brain. The enhanced tracer efflux by blood pressure lowering into the systemic circulation was markedly reduced (- 66.7%) by ligation of lymphatic vessels draining into deep cervical lymph nodes.

CONCLUSIONS

This is the first study showing that cerebrospinal fluid clearance can be improved with acute hypotensive treatment and that the effect of the treatment is reduced by ligation of a lymphatic drainage pathway. Enhanced cerebrospinal fluid clearance by blood pressure lowering may have therapeutic potential in diseases with dysregulated cerebrospinal fluid  flow.

Bilateral Focal Cerebral Angiomatosis Associated with Nervous Signs in a Cat

A case of cerebral angiomatosis in a cat was associated with neurologic signs characterized by clusters of severe generalized seizures. Bilaterally in the gray matter, most prominent in the cingulate gyrus, there was focal accumulation of garlandlike arrangements of blood vessels. Vessels exhibited activated, hypertrophic endothelial cells and thickening and progressive dystrophic mineralization of the basement membrane, with complete luminal obstruction of some affected vessels. Thickening of the basement membrane was due to accumulation of endothelium-derived proteins such as laminin and von Willebrand factor. Furthermore, moderate diffuse astrogliosis was observed. Findings indicate an idiopathic angiomatosis, with clinical signs possibly due to ischemia resulting from narrowing or complete obliteration of vessel lumina. Changes represent a unique endothelial cell-derived lesion within the brain not previously described in humans or domestic animals.

Immunohistochemical examination on the distribution of cells expressed lymphatic endothelial marker podoplanin and LYVE-1 in the mouse tongue tissue

The clinical study for lingual disease requires the detailed investigation of the lingual lymphatic network and lymphatic marker-positive cells. Recently, it has been reported that several tissue cells and leukocytes express lymphatic markers, LYVE-1 and podoplanin. This study was aimed to clarify the lingual distribution of cells expressing LYVE-1 and podoplanin. In the mouse tongue, podoplanin is expressed in nerve sheaths, lingual gland myoepithelial cells, and lymphatic vessels. LYVE-1 is expressed in the macrophage marker Mac-1-positive cells as well as lymphatic vessels, while factor-VIII was detected in only blood endothelial cells. α-SMA was detected in vascular smooth muscle and myoepithelial cells. Therefore, identification of lymphatic vessels in lingual glands, the combination of LYVE-1 and factor-VIII, or LYVE-1 and Mac-1 is useful because myoepithelial cells express podoplanin and α-SMA. The immunostaining of factor-VIII on lymphatic vessels was masked by the immunostaining to LYVE-1 or podoplanin because lymphatic vessels express factor-VIII to a far lesser extent than blood vessels. Therefore, except for the salivary glands, the combination of podoplanin and α-SMA, or factor-VIII is useful to identify lymphatic vessels and blood vessels with smooth muscle, or blood capillaries.

Papillary endothelial hyperplasia and dilated lymphatic vessels in bullous pilomatricoma

This is a report of papillary endothelial hyperplasia in a 9-year-old girl with a pilomatricoma showing bullous appearance. Histologically, papillary proliferation of endothelial cells was found within dilated lymphatic endothelium-lined vascular channels overlying a pilomatricoma. The endothelial cells covering the papillae were of a lymphatic endothelial cell nature proved by immunohistochemistry and electron microscopy. Abundant fibrous long-spacing collagen was observed in the connective tissue and fibroblasts within papillae.

Peroral TAS-202 reduced vessel density in rats with adjuvant-induced arthritis

The present study was designed to investigate blood vessel density interpreted as an indirect measurement of angiogenesis following 4-(3,4,5-trimethoxyphenyl)-6-(2,4,5-trimethoxyphenyl)-2-diethylamino-pyrimidine (TAS-202) treatment in a rat model of arthritis. Male Lewis rats were inoculated intradermally with Mycobacterium butyricum into the hind paw and the arthritic responses were evaluated by measuring the changes in paw volume. Both peroral TAS-202 (10 or 30 mg/kg/day) and indomethacin (1 mg/kg/day) inhibited the autoimmune phase of the arthritic response. However, while the increase in blood vessel density in the synovial tissue was significantly inhibited by TAS-202 (10 and 30 mg/kg/day), indomethacin did not exert this effect (1 mg/kg/day). These results, together with the observation that TAS-202 in combination with indomethacin or prednisolone maintained its ability to exert an antiangiogenic effect, indicate that TAS-202 may offer promise as an oral pro-drug for the treatment of rheumatoid arthritis, through its inhibitory effect on angiogenesis at the inflammation site.

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.

Lymphatic versus blood vascular endothelial growth factors and receptors in humans

Three different growth factor systems have been described acting via endothelial cell-specific receptor tyrosine kinases (RTKs). These are vascular endothelial growth factors (VEGFs), angiopoietins, and ephrins. Recent studies on gene targeting suggest that they play critical roles in embryonic development and contribute to the integrity and responses to environmental factors in the adult vasculature. Coagulation, inflammation, immune response regulation, vascular tone, stromal component synthesis, and angiogenesis are all dependent on the physiological and pathological events that affect endothelial cells in the heart, arteries, veins, and lymphatic vessels. Angiogenesis, the formation of new blood vessels from preexisting ones, takes place in adults only during hormonal control of female reproduction. All other activation of angiogenesis in adulthood occurs in response to injury or pathological processes such as tumorigenesis, diabetes, or inflammatory conditions. Insufficient growth of collateral vessels is a major problem in atherosclerotic cardiovascular disease. Controlled stimulation of angiogenesis would be of therapeutic value. Lymphangiogenesis, the mechanisms involved in the development of lymphatic vessels, was studied intensively nearly a century ago, although since then it has been neglected, perhaps because, unlike the disorders of blood vessels, those of the lymphatic vessels are seldom life-threatening. Interrupting this one-way system can cause severe disorders, including liver dysfunction, genetic disease (e.g., Milroys disease), and degenerative disease (e.g., primary lymphangiosclerosis). Recently, novel growth factors, receptors, cell surface proteins, and transcription factors have been found which play a role in the lymphatic endothelium. These are VEGF-C, VEGF-D, VEGFR-3, LYVE-1, podoplanin, and Prox-1. Until recently lymphatic vessels have been difficult to study due to a lack of appropriate tools. Monoclonal antibodies raised against VEGFR-3 and against its ligands, VEGF-C and VEGF-D, have offered an insight into expression studies in tissues. In this review, we summarize the recent data on VEGFs in the human vasculature.

Histochemical analysis of lymphatic endothelial cells in lymphostasis

The ultrastructure of endothelial cells of intestinal lymphatics and the thoracic duct (TD) and the relation to lymphostasis were examined in rats and monkeys. Localization of 5'-nucleotidase (5'-Nase) and endothelial nitric oxide synthase (eNOS) was studied. In normal lymphatic endothelial cells, 5'-Nase reaction product was evenly deposited on the cell surface in vivo and on cultured TD endothelial cells (TDECs), whereas eNOS was evenly distributed throughout the nucleus and cytoplasm. TDECs had a long filamentous process extending towards the subendothelial extracellular matrix but became flat and regular within 30-40 minutes after gastric perfusion with olive oil. According to their electron-density, two types of cells were found in the TD endothelial layer. The cells with low electron-density exhibited stronger 5'-Nase activity. Valves were bicuspid formations and the valvular endothelial surface of the convex side showed weaker 5'-Nase activity than the concave side. During TD blockage-induced lymphostasis in rats, the 5'-Nase product was almost not discernible in the TDECs within 2 weeks. Larger vesicles were found in the endothelial cytoplasm of the ligated TD. Their number decreased after 6-12 weeks. The small intestinal lymphatics in the mucosa and submucosa were dilated, with numerous open intercellular junctions. The endothelial lining appeared to have reduced activities for 5'-Nase and eNOS in 9 of 11 experimental animals. The results indicated that the inability of the open intercellular junctions, normally working as one-way endothelial flap valves, may be a key morphological feature after TD blockage. Reduced eNOS and 5'-Nase may functionally influence contractile activity and transport capability of the lymphatic vessels in the lymphostasis.

Markers for the lymphatic endothelium: in search of the holy grail?

The ability to discriminate reliably at the histological level between blood and lymphatic microcapillaries would greatly assist the study of a number of biological and pathological questions and may also be of clinical utility. A structure-function comparison of these types of microcapillary suggests that differences which could function as markers to allow discrimination between blood and lymphatic endothelium should exist. Indeed, to date a variety of such markers have been proposed, including basement membrane components, constituents of junctional complexes such as desmoplakin and enzymes such as 5'-nucleotidase. Additionally, a variety of cell surface molecules are thought to be differentially expressed, including PAL-E, VEGFR-3, podoplanin, and LYVE-1. Several of the lymphatic markers proposed in the literature require further characterization to demonstrate fully their lymphatic specificity and some have proven not to be reliable. The relative merits and drawbacks of each of the proposed markers is discussed.

Immunoelectron microscopic study of PECAM-1 expression on lymphatic endothelium of the human tongue

The expression of platelet-endothelial cell adhesion molecule-1 (PECAM-1) on lymphatic and blood vessels of the human tongue was examined with fluorescence and transmission electron microscopy (TEM). The study used anti-desmoplakins antiserum for light microscopic identification of the lymphatic vessels, plus a pre-embedding immunogold electron microscopic technique for TEM observations. Before making TEM observations, cryostat serial sections were immunostained with anti-desmoplakins or anti-PECAM-1 and then embedded. Semithin sections from each cryostat section were photographed under a light microscope and compared in order to identify the lymphatic vessels expressing PECAM-1. In fluorescence microscopy, PECAM-1 expression on lymphatic vessels was weaker than that on blood vessels. TEM observations showed that PECAM-1 expression on the blood vessels was observed only on the luminal surface of the endothelium. In lymphatic vessels, PECAM-1 expression was found both on the luminal and abluminal surfaces of the endothelium. The density of the PECAM-1 reaction products was lower in lymphatic vessels than in blood vessels. The density of PECAM-1 reaction products on the luminal surface of lymphatic vessels was higher than on the abluminal surfaces. The results suggest that blood vessels are more active than lymphatic vessels in leukocyte migration. The expression of PECAM-1 on the abluminal surface of lymphatic endothelium may allow leukocytes to adhere to the endothelium and interact in their migration from tissue into lymphatic vessels.

Cerebral vascular hamartomas in five dogs

Vascular hamartomas are considered developmental lesions rather than true neoplasms. Reports of such anomalies in the canine brain are scarce, and their classification is confusing. This case series of vascular hamartomas from the brains of five dogs was characterized using histochemistry and immunohistochemistry, in addition to gross and microscopic findings. All five hamartomas were located in the telencephalon, three in the pyriform lobe, without any predilection for the left or right side. Each hamartoma consisted of a proliferation of thin-walled vessels which varied in caliber. These vessels were elastin-negative, with varying amounts of collagen and no muscular component. In four of the five hamartomas, lining cells were actin- and factor VIII-positive. All five hamartomas contained glial fibrillary acid protein (GFAP)-positive parenchyma at moderate to high frequency, and four contained neurofilament-positive axons between component vessels. This report shows that vascular hamartomas in the canine brain are structural malformations for which immunohistochemistry is useful for accurate classification.

Desmoplakin as a specific marker of lymphatic vessels

The usefulness of immunostaining with anti-desmoplakin antibody for light microscopic identification of lymphatic vessels was examined in cryostat sections of the human tongue. The results were compared with laminin, 5'-nucleotidase (5'-Nase), and factor VIII staining. Immunoelectron microscopic observation was also performed to confirm that the vessels reacting with anti-desmoplakin were lymphatic vessels. Under the immunoelectron microscopic, the vessels reacting with anti-desmoplakin showed ultrastructural features characteristic of lymphatic vessels: thin endothelial walls, no or incomplete basal lamina, open junctions, and overlapping endothelium. In general, lymphatic vessels identified by anti-desmoplakin reacted strongly with 5'-Nase, but showed weak or no reactivity with anti-laminin and anti-factor VIII. Blood vessels showed no reactivity with anti-desmoplakin, but reacted strongly with anti-laminin and anti-factor VIII. However, some blood and lymphatic vessels showed intermediate reactivity with anti-laminin, anti-factor VIII, and 5'-Nase. It was difficult to identify these as blood or lymphatic vessels only by the reactivity differences. The results indicate that anti-desmoplakin antibody specifically distinguishes lymphatic vessels and is useful for studying the fine distribution of lymphatic vessels under light microscopy.

Trehalose 6,6'-dimycolate (cord factor) of Mycobacterium tuberculosis induces corneal angiogenesis in rats

Neovascularization or angiogenesis is required for the progression of chronic inflammation. The mechanism of inflammatory neovascularization in tuberculosis remains unknown. Trehalose 6, 6'-dimycolate (TDM) purified from Mycobacterium tuberculosis was injected into rat corneas. TDM challenge provoked a local granulomatous response in association with neovascularization. Neovascularization was seen within a few days after the challenge, with the extent of neovascularization being dose dependent, although granulomatous lesions developed 14 days after the challenge. Cytokines, including tumor necrosis factor alpha (TNF-alpha), interleukin-8 (IL-8), IL-1beta, and vascular endothelial growth factor (VEGF), were found in lesions at the early stage (within a few days after the challenge) and were detectable until day 21. Neovascularization was inhibited substantially by neutralizing antibodies to VEGF and IL-8 but not IL-1beta. Treatment with anti-TNF-alpha antibodies resulted in partial inhibition. TDM possesses pleiotropic activities, and the cytokine network plays an important role in the process of neovascularization.

Blood flow influences vascular growth during tumour angiogenesis

Many factors play a role in tumour angiogenesis. We observed growing tumour vessels in vivo to study the relationship between blood flow and vascular enlargement. Mammary adenocarcinoma was implanted into Fisher-344 rat with dorsal skin-fold transparent chambers. Vascular growth was observed and recorded on videotape through a microscope for 6 h. Vascular networks were photographed and traced every 30 min to identify changes over time. Tumour sections were stained with Masson's trichrome and anti-Factor VIII-related antigen. Tumour growth was rapid enough for differences to be seen each hour. Vessels with a high blood flow showed an increase in diameter within a few hours and new branches formed from these vessels. In contrast, vessels without an increase in blood flow showed no change in diameter. Vessels within the interstitium surrounding the tumour were lined by endothelium that was positive for anti-Factor VIII-related antigen staining. Vessels in the tumour had extremely rare endothelial cells detectable by Masson's trichrome or anti-Factor VIII-related antigen staining. In conclusion, increased blood flow may cause vascular enlargement and some primitive vessels seem to lack endothelium.

Immunohistochemical demonstration of lymphatic vessels in human dental pulp

The existence of lymphatic vessels in dental pulp has been a matter of continuing controversy because of the difficulty of discriminating them in ordinary stained tissue sections. Recently, we have succeeded in establishing a new identification method for lymphatic vessels in human frozen sections by using a commercial monoclonal antibody specific for the human thoracic duct and anti-human laminin antiserum. The present study aimed to examine the lymphatic vessels in human dental pulp using the new immunostaining method, and compared the results with those in human small intestine. The study clearly demonstrated the distribution of lymphatic vessels in human dental pulp. Large lymphatic vessels are located in the central part of the pulp and there are small lymphatic vessels in the periphery of the pulp. This suggests that lymphatic drainage of the human dental pulp starts from the periphery of the pulp and collects in the central part of the pulp. A notable difference between the small intestine and dental pulp was found in the immunoreactivity of lymphatic vessels to anti-human laminin anti-serum. In small intestine, immunoreactivity was significantly weaker than that of the blood vessels, whereas in dental pulp, that of lymphatic vessels was almost the same as blood vessels, except for some lymphatic vessels showing very weak reactivity. These findings suggest that the development of the basement membrane in both the lymphatic and blood vessels of human dental pulp is not as marked as in other tissue.

Angiogenesis as an unfavorable factor related to lymph node metastasis in early gastric cancer

BACKGROUND

Recent studies suggest that angiogenesis enhances tumor growth and metastasis. Lymph node metastasis influences the prognosis and selection of treatment modalities in cancers. In this study, the authors investigated the correlation between angiogenesis and clinicopathologic features to determine whether angiogenesis correlated with lymph node metastasis in early-stage gastric cancer.

METHODS

A total of 97 specimens from patients with early gastric cancer were studied by immunohistochemical methods using anti-Factor VIII-related antigen antibody.

RESULTS

Tumor size was significantly correlated with microvessel count, which increased as tumor size increased. Microvessel counts from tumors with lymphatic vessel invasion, lymph node metastasis, and submucosal invasion were significantly higher than those without. Furthermore, microvessel count was an independent factor that influenced lymph node metastasis (P = .0016) by multivariate logistic regression analysis.

CONCLUSION

In the early stage of gastric carcinoma, angiogenesis is an independent factor that impacts on lymph node metastasis.

Intraabdominal lymphangiosarcoma in a Fischer-344 rat

A Sarcoma arising in the abdominal cavity in an aged Fischer-344 rat was studied by immunohistochemistry and electron microscopy. The white-yellow soft mass was located on the lumbosacral vertebrae, compressing adjacent parenchymal organs. The tumor was made up of spindle shaped cells situated in a background of myxoid substance and a small amount of reticulin and collagen fibers. The tumor cells grew in a loose storiform pattern and often adhered to each other by their cell processes to form ovoid or slitlike spaces. Immunohistochemically, the tumor cells were strongly positive for vimentin but negative for keratin, macrophage ED1 antigen, alpha-smooth muscle actin, Factor VIII-related antigen, and S100 protein. Electron microscopy demonstrated the endothelial differentiation of the tumor cells, such as occasional luminal spaces, a small number of micropinocytotic vesicles, and interdigitating junctions with desmosomes between cell processes of adjacent cells. Furthermore, its endothelial origin was suggested by the presence of electron-dense rods resembling Weibel-Palade bodies. Instead of a definitive basement lamina surrounding the tumor cells, there were extracellular thin "anchoring filaments" that were attached to the cell surface at areas of increased electron density. These findings indicate that the tumor is of lymphatic vessel type rather than blood vessel type.

Identification of lymphatic vessels by using a monoclonal antibody specific for the human thoracic duct

Light microscopic identification of lymphatic vessels of the human small intestine was studied immuno-histochemically with a monoclonal antibody specific for human thoracic duct (mAb-D) and rabbit anti-human laminin antibody (anti-L). Two types of vessels were observed with anti-L; one strongly reacted with regularly outlined vessels and the other weakly reacted with irregularly outlined vessels and thin walls. Immunoreactivity to mAb-D was strong in the weakly reacting vessels, and the strongly reacting vessels did not react to mAb-D. Immunoreactivity of lymphatic vessels to anti-L has been reported to be weaker than that of the blood vessels; only irregularly outlined vessels which were weakly immunostained with anti-L reacted to mAb-D and no cross-reaction to mAb-D was observed in the regularly outlined vessels. This indicates that the vessels strongly reacting with anti-L are blood vessels and the vessels immunostained with mAb-D must be lymphatics. The study shows that it is possible to identify lymphatic vessels light microscopically by mAb-D. This method will be useful in studying the fine distribution of lymphatic vessels in normal tissue and also in pathological tissue such as metastasis of malignant tumors.

Basic fibroblast growth factor may repair experimental cerebral aneurysms in rats

BACKGROUND AND PURPOSE

To determine whether basic fibroblast growth factor (FGF) can induce proliferative response of endothelial cells and/or smooth muscle cells in aneurysmal lesions, we investigated the effect of the intravenous administration of basic FGF on experimental cerebral aneurysms.

METHODS

Cerebral aneurysms were induced in rats by ligation of the unilateral common carotid artery, producing hypertension. Three months later, basic FGF was intravenously injected in two groups of randomly divided rats on days 1, 3, and 5 at two different doses (low dose: 2 micrograms/100 g body wt per day; high dose: 5 micrograms/100 g body wt per day). In a control group, normal saline was similarly injected. The junctions of the anterior cerebral artery (ACA) and the olfactory artery (OA) were examined with a light microscope. Aneurysmal changes were defined as the lesions with discontinuity of the internal elastic lamina in more than half of the outward dilated wall. Depending on whether the smooth muscle cell layer was present in the whole wall, the lesions were divided into two stages: early aneurysmal lesion (whole area) and saccular aneurysm (not totally preserved).

RESULTS

The control and the low-dose groups presented no obvious intimal thickening in the intact ACA-OA junctions of both nonligated and ligated sides as well as in the aneurysmal changes. In contrast, in the high-dose group, various degrees of intimal thickening in the wall were detected in 7 of 15 early aneurysmal lesions (P = .019, Fisher's exact test). Immunohistochemistry showed the proliferated cells to be smooth muscle cells.

CONCLUSIONS

These results demonstrate that exogenous basic FGF induces the proliferative response of smooth muscle cells in aneurysmal lesions in rats.

Histopathological study of lymphatic invasion in squamous cell carcinoma (O-1N) with high potential of lymph node metastasis

The process of lymph node metastasis was studied in an animal model (termed O-1N) that was successfully established using a metastatic tumor to the submandibular lymph node from a chemically induced squamous cell carcinoma of the hamster tongue. The model has been maintained by serial transplantation of metastatic tumors into the buccal pouch. Lymphovascular invasion of transplanted O-1N in the tongue was examined in serial histologic sections. Lymphatic vessels were distinguished from blood vessels by Masson's trichrome stain for vascular smooth muscle, BSA-I lectin binding for vascular endothelium, and laminin and type IV collagen immunostaining for the vascular basement membrane. Transplanted tumors enlarged progressively with invasion of surrounding tissues of the tongue and resulted in lymph node metastasis in all animals with successful takes. Local growth of the tumors in the tongue was accompanied by stromal proliferation with abundant dilated lymphatic vessels which contained clusters of tumor cells. On serial sections, the carcinoma cell clusters in lymphatics in the close proximity of tumor nests were in continuity with adjacent tumor nests, whereas such continuity was not recognized in those occurring apart from tumor nests. The formation of isolated carcinoma cell clusters resulting from disintegration of elongated processes of tumor nests with invasion of lymphatics and subsequent transport in lymphatics and deposition in lymph nodes in clusters were well demonstrated in other serial sections. The key step of lymph node metastasis therefore appears to be direct invasion of lymphatic vessels by tumor cells, similar to their invasion of adjacent tissues but different from the way that blood cells escape through vessel walls. Proliferation of lymphatics around tumor nests and transport of tumor cells in clusters would also contribute to the production of metastatic deposits in lymph nodes.

Benign lymphangioendothelioma

We describe a 40-year-old white man with a red-brown, indurated plaque on the proximal aspect of his right thigh. The lesion had been present since birth, and the patient had a 20-year clinical history of recurrent cellulitis in the same area. The histopathologic features of the lesion included permeation of the dermis by flattened, endothelium-lined channels without cellular atypia, hemorrhage, or inflammation. The endothelial cells were stained intensely with monoclonal antibody anti-CD34 (clone MY10). In addition, antibodies to factor VIII antigen, HLA-DR, smooth muscle actin, ICAM-1, and the lectin Ulex europaeus labeled the luminal cells. The basement membrane of the channels stained with anti-type IV collagen and laminin. Desmin-positive cells were abundant adjacent to the channels. Factor XIIIa stained both mononuclear cells and occasional dendritic cells in the perivascular area. Ki-67 immunolabeling could not be demonstrated on fresh or frozen tissue. Electron microscopy revealed the presence of both tight junctions and a well-formed, continuous basement membrane but the absence of Weibel-Palade bodies.

Lymphatic vessels of the human dental pulp in different conditions

The characteristics of the lymphatic vessel endothelial wall have been investigated in human normal and inflamed dental pulps. In normal pulps the endothelial wall is characterized by the presence of micropinocytotic vesicles and intraparietal channels. In the inflamed pulpal tissue, where an increase in interstitial fluid pressure occurs, the distended endothelial wall presents open junctions between endothelial cells and the openings of the intraparietal channels. Moreover the micropinocytotic vesicles disappear. The cytoplasm of the endothelial cells is characterized by the presence of numerous Weibel-Palade bodies, which increase in number in the dilated vessels. In the fibrillar apparatus surrounding the lymphatic vessel wall collagen fibrils are the prevalent component, while elastic fibers are not present. The different morphological properties of the lymphatic vessels are compared and discussed with regard to the variation of the functional conditions of the tissue.