Vascular endothelial growth factor receptor-3 in lymphangiogenesis in wound healing

Vascular endothelial growth factor receptor-3 (VEGFR-3) is essential for embryonic cardiovascular development, but thereafter becomes confined to the lymphatic endothelium in adult tissues. We have here studied VEGFR-3 expression in experimental wounds of pigs and chronic inflammatory wounds of humans. In healing incisional and punch biopsy wounds made in the dorsal skin of pigs, angiogenic blood vessels, identified by use of the blood vascular endothelial markers vWF and PAL-E and the basal lamina protein laminin, developed into the granulation tissue stroma from day 4 onward, being most abundant on days 5 and 6 and regressing thereafter. VEGFR-3-positive vessels were observed in the granulation tissue from day 5 onward. These vessels were distinct from the PAL-E/laminin/vWF-positive vessels and fewer in number, and they appeared to sprout from pre-existing VEGFR-3-positive lymphatic vessels at the wound edge. Unlike the blood vessels, very few VEGFR-3-positive lymphatic vessels persisted on day 9 and none on day 14. In chronic wounds such as ulcers and decubitus wounds of the lower extremity of humans, VEGFR-3 was also weakly expressed in the vascular endothelium. Our results suggest that transient lymphangiogenesis occurs in parallel with angiogenesis in healing wounds and that VEGFR-3 becomes up-regulated in blood vessel endothelium in chronic inflammatory wounds.     

Expression of vascular endothelial growth factor receptor 3 in blood and lymphatic vessels of lung adenocarcinoma

Vascular endothelial growth factor receptor 3 (VEGFR-3) has been proposed as a marker for lymphatic endothelial cells. This study investigated the expression of VEGFR-3 in the tumour vessels of lung adenocarcinoma and evaluated whether VEGFR-3 staining was useful for identifying lymphatic vessels within the tumour stroma. It also explored whether active growth of lymphatic vessels occurred in lung adenocarcinoma. Formalin-fixed, paraffin-embedded specimens obtained from 60 cases of lung adenocarcinoma, including five cases of pure bronchiolo-alveolar carcinoma (BAC) without stromal, vascular, and pleural invasion, were examined. No VEGFR-3-positive vessels were observed in pure BAC, but varying numbers of VEGFR-3-positive vessels were found in 39 of 55 (70.9%) invasive adenocarcinomas. A comparison of serial sections stained for VEGFR-3, CD31, and laminin-1 showed that most of the VEGFR-3-positive vessels appeared to be blood vessels (CD31-positive, laminin-1-positive), but some had the characteristics of lymphatic vessels (variable staining for CD31, little or no staining for laminin-1). VEGFR-3 staining highlighted lymphatic invasion by cancer cells; this invasion could not be detected by CD31 or haematoxylin and eosin (H&E) staining. Active growth of lymphatic vessels (as indicated by nuclear Ki-67 labelling of the endothelium) was observed in five tumours, four of which showed a high level of lymphatic invasion by cancer cells. It was concluded that VEGFR-3 immunostaining did not discriminate clearly between vascular and lymphatic endothelial cells, since expression of VEGFR-3 can be up-regulated in tumour blood vessels. However, VEGFR-3 staining combined with laminin-1 and CD31 staining would be useful for identifying lymphatic vessels and their invasion by tumour cells in a more objective way. Finally, proliferation of lymphatic endothelial cells may occur in association with lymphatic invasion by cancer cells.     

血管内皮生长因子C及其受体3在人恶性黑色素瘤组织内的表达及意义

目的 观察人恶性黑色素瘤组织内血管内皮生长因子C(VEGF-C)及其受体3(VEGFR-3)的表达,探讨VEGF-C和VEGFR-3在恶性黑色素瘤淋巴管生成及淋巴道转移中的作用.方法 取人恶性黑色素瘤组织48例(石蜡标本30例,术后新鲜组织18例),应用免疫组织化学和RT-PCR技术,观察VEGF-C和VEGFR-3蛋白及mRNA在恶性黑色素瘤组织内的表达情况.以淋巴管内皮透明质酸受体(LYVE-1)标记淋巴管,计数恶性黑色素瘤组织淋巴管数密度.结果 VEGF-C和VEGFR-3蛋白主要表达于恶性黑色素瘤细胞胞浆内,在肿瘤周围的血管和淋巴管内皮上也可见VEGFR-3蛋白表达,VEGF-C和VEGFR-3蛋白在淋巴结转移组恶性黑色素瘤组织内的表达水平明显高于无淋巴结转移组(P<0.05).在18例新鲜恶性黑色素瘤中,淋巴结转移组VEGF-C和VEGFR-3mRNA的表达明显高于无淋巴结转移组(P<0.01).LYVE-1表达于肿瘤间质内的淋巴管内皮细胞,淋巴结转移组恶性黑色素瘤组织中的淋巴管数密度(LMVD)为9.845±2.454,无淋巴结转移组恶性黑色素瘤组织中的淋巴管数密度为6.534±2.193,淋巴结转移组恶性黑色素瘤组织内的淋巴管数密度明显高于无淋巴结转移组(P<0.01).结论恶性黑色素瘤组织内VEGF-C表达明显增高,并通过上调其受体VEGFR-3的表达促进恶性黑色素瘤组织内淋巴管的生成,从而促进恶性黑色素瘤的淋巴道转移.     

CD40 ligation induces tissue factor expression in human vascular smooth muscle cells

Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are important regulators of blood and lymphatic vessel growth and vascular permeability. Both blood and lymphatic vessels of the upper respiratory tract play important roles in pathological conditions, such as infections and tumors. Here we have studied the expression of VEGF-C and its receptor VEGFR-3 in the upper respiratory system by Northern blot analysis and immunohistochemistry of human tissues, and in situ mRNA hybridization of developing mouse embryos and β-galactosidase staining of mouse embryos having a LacZ marker gene in the VEGFR-3 gene locus. The results demonstrate expression of VEGF-C and VEGFR-3 in the developing and adult nasal respiratory epithelium and in the nasal vascular plexus, respectively. Unlike in most other tissues, in the nasal mucosa VEGFR-3 is expressed in both blood and lymphatic vessels. Expression of VEGF-C was also detected in nasal and nasopharyngeal tumor islands, which were surrounded by VEGFR-3-positive angiogenic blood vessels. These results suggest that VEGF-C and VEGFR-3 have a role in the development of the nasal submucosal vascular plexus and in its normal function and that they are associated with angiogenesis in nasal and nasopharyngeal tumors.     

VEGF-D in association with VEGFR-3 promotes nodal metastasis in human invasive lobular breast cancer

We assessed the expression of vascular endothelial growth factors (VEGF-C and VEGF-D) in breast cancer cells and the density of lymph vessels and VEGF receptor-3 (VEGFR-3)-positive vessels in and around the tumor in invasive lobular breast cancer. We found significant correlation between peritumoral lymph vessel density and presence of lymph node metastases (P=.001) and the number of metastatic lymph nodes (P<.001). A significant correlation was detected between tumor cell VEGF-D expression and lymph node status (P=.001) and density of lymphatic vessel endothelial receptor (LYVE)-1-positive vessels (P=.035). VEGFR-3+/VEGF-D+ and VEGFR-3+/VEGF-C+ tumors had a significantly higher number of metastatic lymph nodes than tumors with other staining patterns (P<.001). Tumors positive for neither VEGF-D nor VEGFR-3 had a lower density of LYVE-1+ vessels than tumors with other staining patterns (P=.033). Our results indicate that peritumoral lymph vessel density is associated with lymph node metastases in invasive lobular breast cancer and that invasive lobular cancer producing VEGF-D, surrounded by VEGFR-3+ vessels, has a significantly higher peritumoral lymph vessel density and a higher number of metastatic lymph nodes.     

VEGFR-3 and Its Ligand VEGF-C Are Associated with Angiogenesis in Breast Cancer

Recently, monoclonal antibodies against the human vascular endothelial growth factor receptor VEGFR-3 were shown to provide a specific antigenic marker for lymphatic endothelium in various normal tissues. In this study we have investigated the expression of VEGFR-3 and its ligand VEGF-C in normal breast tissue and in breast tumors by immunohistochemistry. VEGFR-3 was weakly expressed in capillaries of normal breast tissue and in fibroadenomas. In intraductal breast carcinomas, VEGFR-3 was prominent in the "necklace" vessels adjacent to the basal lamina of the tumor-filled ducts. VEGF receptor 1 and 2 as well as blood vessel endothelial and basal lamina markers were colocalized with VEGFR-3 in many of these vessels. Antibodies against smooth muscle alpha-actin gave a weak staining of the necklace vessels, suggesting that they were incompletely covered by pericytes/smooth muscle cells. A highly elevated number of VEGFR-3 positive vessels was found in invasive breast cancer in comparison with histologically normal breast tissue (P < 0.0001, the Mann-Whitney test). VEGF-C was located in the cytoplasm of intraductal and invasive cancer cells. The results demonstrate that the expression of VEGFR-3 becomes up-regulated in the endothelium of angiogenic blood vessels in breast cancer. The results also suggest that VEGF-C secreted by the intraductal carcinoma cells acts predominantly as an angiogenic growth factor for blood vessels, although this paracrine signaling network between the cancer cells and the endothelium may also be involved in modifying the permeabilities of both blood and lymphatic vessels and metastasis formation.     

VEGFR-3 in adult angiogenesis.

Vascular endothelial growth factor receptor 3 (VEGFR-3, Flt-4), the receptor for vascular endothelial growth factors (VEGFs) C and D, is expressed on lymphatic endothelium and may play a role in lymphangiogenesis. In embryonic life, VEGFR-3 is essential for blood vessel development. The purpose of this study was to investigate whether VEGFR-3 is also involved in blood vessel angiogenesis in the adult. This was studied in human tissues showing angiogenesis and in a model of VEGF-A-induced iris neovascularization in the monkey eye, by the use of immunohistochemistry at the light and electron microscopic level. VEGFR-3 was expressed on endothelium of proliferating blood vessels in tumours. In granulation tissue, staining was observed in the proliferative superficial zone in plump blood vessel sprouts, in the intermediate zone in blood vessels and long lymphatic sprouts, and in the deeper fibrous zone in large lymphatics, in a pattern demonstrating that lymphangiogenesis follows behind blood vessel angiogenesis in granulation tissue formation. At the ultrastructural level, VEGFR-3 was localized in the cytoplasm and on the cell membrane of endothelial cells of sprouting blood vessels and sprouting lymphatics. In monkey eyes injected with VEGF-A, blood vessel sprouts on the anterior iris surface and pre-existing blood vessels in the iris expressed VEGFR-3. In conclusion, these results support a role for VEGFR-3 and its ligands VEGF-C and/or VEGF-D in cell-to-cell signalling in adult blood vessel angiogenesis. The expression of VEGFR-3 in VEGF-A-induced iris neovascularization and in pre-existing blood vessels exposed to VEGF-A suggests that this receptor and possibly its ligands are recruited in VEGF-A-driven angiogenesis.     

Transgenic induction of vascular endothelial growth factor-C is strongly angiogenic in mouse embryos but leads to persistent lymphatic hyperplasia in adult tissues

Vascular endothelial growth factor-C (VEGF-C) is the quintessential lymphangiogenic growth factor that is required for the development of the lymphatic system and is capable of stimulating lymphangiogenesis in adults by activating its receptor, VEGFR-3. Although VEGF-C is a major candidate molecule for the development of prolymphangiogenic therapy for defective lymphatic vessels in lymphedema, the stability of lymph vessels generated by exogenous VEGF-C administration is not currently known. We studied VEGF-C-stimulated lymphangiogenesis in inducible transgenic mouse models in which growth factor expression can be spatially and temporally controlled without side effects, such as inflammation. VEGF-C induction in adult mouse skin for 1 to 2 weeks caused robust lymphatic hyperplasia that persisted for at least 6 months. VEGF-C induced lymphangiogenesis in numerous tissues and organs when expressed in the vascular endothelium in either neonates or adult mice. Very few or no effects were observed in either blood vessels or collecting lymph vessels. Additionally, VEGF-C stimulated lymphangiogenesis in embryos after the onset of lymphatic vessel development. Strikingly, a strong angiogenic effect was observed after VEGF-C induction in vascular endothelium at any point before embryonic day 16.5. Our results indicate that blood vessels can undergo VEGF-C-induced angiogenesis even after down-regulation of VEGFR-3 in embryos; however, transient VEGF-C expression in adults can induce long-lasting lymphatic hyperplasia with no obvious side effects on the blood vasculature.     

Monoclonal antibody D2-40, a new marker of lymphatic endothelium, reacts with Kaposi's sarcoma and a subset of angiosarcomas.

There is controversy over the histogenesis of Kaposi's sarcoma (KS) from lymphatic or blood vessel endothelium. D2-40 is a novel monoclonal antibody to an Mr 40,000 O-linked sialoglycoprotein that reacts with a fixation-resistant epitope on lymphatic endothelium. We sought to establish the selectivity of D2-40 for lymphatic endothelium in normal tissues and compare its reactivity with the expression of the widely used vascular endothelial marker CD31 in a series of 62 formalin-fixed and paraffin-embedded vascular lesions including KS. In normal tissues, D2-40 stained the endothelium of lymphatic channels but not of blood vessels, including arteries and capillaries defined by reactivity with the blood vessel endothelial marker PAL-E. In our series of vascular lesions, D2-40 stained lymphangiomas (10/10), benign tumors of undisputed lymphatic origin, but not benign neoplasms or tumorlike lesions of blood vessel origin, including hemangiomas (0/10), glomus tumors (0/3), angiolipomas (0/2), pyogenic granulomas (0/2), vascular malformations (0/2), hemangiopericytoma (0/1), or hemangioendothelioma (0/1). D2-40 stained all cases of cutaneous KS (24/24) at all stages of progression, including patch, plaque, and nodular stages, supporting the concept that this disease originates from a cell type capable of undergoing lymphatic differentiation. D2-40 also stained three of seven angiosarcomas, indicating that a subset of these tumors can undergo at least partial differentiation along the lymphatic endothelial lineage and could be classified as lymphangiosarcomas. In comparison, CD31 was expressed in all benign and malignant vascular lesions, except for glomus tumors (0/3) and 5/10 lymphangiomas, in which staining was absent. We conclude that D2-40 is a new selective marker of lymphatic endothelium in normal tissues and vascular lesions and is valuable for studying benign and malignant vascular disorders in routinely processed tissue specimens.     

B lymphocyte-specific c-Myc expression stimulates early and functional expansion of the vasculature and lymphatics during lymphomagenesis

Expression of the c-myc proto-oncogene is deregulated in many human cancers. We examined the role of c-Myc in stimulating angiogenesis and lymphangiogenesis in a highly metastatic murine model of Burkitt's lymphoma (E micro -c-myc), where c-Myc is expressed exclusively in B lymphocytes. Immunohistochemical analysis of bone marrow and lymph nodes from young (preneoplastic) E micro -c-myc transgenic mice revealed increased growth of blood vessels, which are functional by dye flow assay. Lymphatic sinuses also increased in size and number within the lymph nodes, as demonstrated by immunostaining for with a lymphatic endothelial marker 10.1.1. The 10.1.1 antibody recognizes VEGFR-2- and VEGFR-3-positive lymphatic sinuses and vessels within lymph nodes, and also recognizes lymphatic vessels in other tissues. Subcutaneously injected dye traveled more efficiently through draining lymph nodes in E micro -c-myc mice, indicating that these hypertrophic lymphatic sinuses increase lymph flow. Purified B lymphocytes and lymphoid tissues from E micro -c-myc mice expressed increased levels of vascular endothelial growth factor (VEGF) by immunohistochemical or immunoblot assays, which could promote blood and lymphatic vessel growth through interaction with VEGFR-2, which is expressed on the endothelium of both vessel types. These results indicate that constitutive c-Myc expression stimulates angiogenesis and lymphangiogenesis, which may promote the rapid growth and metastasis of c-Myc-expressing cancer cells, respectively.     

血管内皮生长因子受体3和Podoplanin在人结肠癌组织中的表达

目的:观察血管内皮生长因子受体3(vascular endothelial growth factor receptor-3,VEGFR-3)和Podoplanin在人结肠癌组织中的表达,以探讨二者标记淋巴管的特异性。方法:选择55例人结肠癌组织标本,应用免疫组织化学法观察VEGFR-3和Podoplanin在人结肠癌组织中的表达。结果:Podoplanin主要表达于淋巴管内皮细胞上,微血管极少着色;VEGFR-3主要表达于淋巴管内皮细胞上,另外在小血管内皮也有较丰富的表达。结论:Podoplanin在淋巴管内皮细胞的表达具有较高特异性,可以用来标记淋巴管。     

Lymphangiogenic growth factor responsiveness is modulated by postnatal lymphatic vessel maturation

Lymphatic vessel plasticity and stability are of considerable importance when attempting to treat diseases associated with the lymphatic vasculature. Development of lymphatic vessels during embryogenesis is dependent on vascular endothelial growth factor (VEGF)-C but not VEGF-D. Using a recombinant adenovirus encoding a soluble form of their receptor VEGFR-3 (AdVEGFR-3-Ig), we studied lymphatic vessel dependency on VEGF-C and VEGF-D induced VEGFR-3 signaling in postnatal and adult mice. Transduction with AdVEGFR-3-Ig led to regression of lymphatic capillaries and medium-sized lymphatic vessels in mice under 2 weeks of age without affecting collecting lymphatic vessels or the blood vasculature. No effect was observed after this period. The lymphatic capillaries of neonatal mice also regressed partially in response to recombinant VEGFR-3-Ig or blocking antibodies against VEGFR-3, but not to adenovirus-encoded VEGFR-2-Ig. Despite sustained inhibitory VEGFR-3-Ig levels, lymphatic vessel regrowth was observed at 4 weeks of age. Interestingly, whereas transgenic expression of VEGF-C in the skin induced lymphatic hyperplasia even during embryogenesis, similar expression of VEGF-D resulted in lymphangiogenesis predominantly after birth. These results indicate considerable plasticity of lymphatic vessels during the early postnatal period but not thereafter, suggesting that anti-lymphangiogenic therapy can be safely applied in adults.     

Vascular endothelial growth factor receptor-3 (VEGFR-3): a marker of vascular tumors with presumed lymphatic differentiation, including Kaposi's sarcoma, kaposiform and Dabska-type hemangioendotheliomas, and a subset of angiosarcomas.

Recently, a novel monoclonal antibody to vascular endothelial growth factor receptor 3 (VEGFR-3), a tyrosine kinase receptor expressed almost exclusively by lymphatic endothelium in the adult, has been shown to react with a small number of cases of Kaposi's sarcoma (KS) and cutaneous lymphangiomas. We sought to extend these studies to a large number of well-characterized vascular neoplasms to evaluate diagnostic uses of this antibody and to determine whether it defines them in a thematic fashion. Formalin-fixed, paraffin-embedded sections from 70 vascular tumors were immunostained with antibodies to VEGFR-3 von Willebrand factor (vWF), and CD31. Anti-VEGFR-3 was positive in 23 of 24 KS, 8 of 16 angiosarcomas (AS), 6 of 6 kaposiform hemangioendotheliomas, 4 of 4 Dabska tumors, and 2 of 13 hemangiomas. Positively staining angiosarcomas were characterized either by a prominent lymphocytic component, a hobnail endothelial cell similar to that encountered in the Dabska tumor, or spindled areas resembling KS. No VEGFR-3 expression was noted in any cases of epithelioid hemangioendothelioma, pyogenic granuloma, littoral angioma, or stasis dermatitis. vWF expression was seen in 10 of 13 KS; 13 of 14 AS; 4 of 5 kaposiform hemangioendotheliomas; and all Dabska tumors, hemangiomas, lymphangiomas, epithelioid hemangioendotheliomas, vascular malformations, stasis dermatitis, and splenic littoral angiomas. CD31 expression was present in 12 of 13 KS, 13 of 14 AS, and in all other cases. Expression of VEGFR-3 is a very sensitive marker of KS, kaposiform, and Dabska-type hemangioendotheliomas, suggesting that all show at least partial lymphatic endothelial differentiation. Expression of VEGFR-3 does not reliably discriminate KS from AS. However, the expression of VEGFR-3 by certain AS having Kaposi-like areas, a prominent lymphocytic infiltrate, or hobnail endothelium may define subset(s) having phenotypic, if not pathogenetic and biologic, differences.     

血管内皮生长因子C在小鼠碱烧伤角膜内的表达及意义

目的观察血管内皮生长因子C(VEGF-C)在小鼠角膜碱烧伤后不同时间段角膜组织内的表达情况,探讨VEGF-C在小鼠角膜碱烧伤后新生淋巴管形成过程中的作用。方法制作小鼠角膜碱烧伤模型,分别于碱烧伤后1d、3d、5d、7d、12d和18d取材。采用免疫组化法(SP),观察VEGF-C在正常角膜和碱烧伤后不同时间段角膜组织内的表达情况。应用淋巴管内皮透明质酸受体(LYVE-1)标记淋巴管,观察小鼠碱烧伤角膜内新生淋巴管的形成情况。结果在正常小鼠角膜组织内,VEGF-C表达于角膜上皮层和内皮层。在碱烧伤角膜内,VEGF-C主要表达于角膜基质内入侵的炎性细胞和角膜上皮层细胞,并且表达增高,于碱烧伤后3d,VEGF-C的表达达到高峰(P<0.01)。碱烧伤后7d,VEGF-C的表达下降至正常水平,可见阳性表达LYVE-1的处于开放状态的新生淋巴管。结论VEGF-C可能参与小鼠角膜碱烧伤后角膜新生淋巴管形成过程。     

Vascular endothelial growth factor C is required for sprouting of the first lymphatic vessels from embryonic veins

Lymphatic vessels are essential for immune surveillance, tissue fluid homeostasis and fat absorption. Defects in lymphatic vessel formation or function cause lymphedema. Here we show that the vascular endothelial growth factor C (VEGF-C) is required for the initial steps in lymphatic development. In Vegfc-/- mice, endothelial cells commit to the lymphatic lineage but do not sprout to form lymph vessels. Sprouting was rescued by VEGF-C and VEGF-D but not by VEGF, indicating VEGF receptor 3 specificity. The lack of lymphatic vessels resulted in prenatal death due to fluid accumulation in tissues, and Vegfc+/- mice developed cutaneous lymphatic hypoplasia and lymphedema. Our results indicate that VEGF-C is the paracrine factor essential for lymphangiogenesis, and show that both Vegfc alleles are required for normal lymphatic development.     

The lymphatic endothelium of the avian wing is of somitic origin.

It has recently been shown that there are lymphangioblasts in the early avian wing bud, but fate map studies on the origin of these cells have not yet been performed. The lymphatics in the wings of 10-day-old chick and quail embryos are characterized by both the position along with all major blood vascular routes and by the Vascular Endothelial Growth Factor Receptor-3 (VEGFR-3) expression. In the quail, the endothelium of both blood vessels and lymphatics can be marked with the QH1 antibody. We have grafted the dorsal halves of epithelial somites of 2-day-old quail embryos homotopically into chick embryos. The grafting was performed at the wing level and the host embryos were reincubated until day 10. The chimeric wings were studied with the QH1 antibody alone and with double staining consisting of VEGFR-3 in situ hybridization and QH1 immunofluorescence. Our results show that in the wing the endothelium of both the blood vessels and the lymphatics is derived from the somites. QH1-positive endothelial cells form the vasculature of the chimeric wings. Chimeric lymphatics of the wing can be identified because of their typical position and their VEGFR-3 and QH1 double-positivity. This shows that not only the blood vascular cells but also the lymphatic endothelial cells of the avian wing are born in the paraxial/somitic mesoderm.     

Localization of vascular endothelial growth factor-D in malignant melanoma suggests a role in tumour angiogenesis

Expression of angiogenic and lymphangiogenic factors by tumours may influence the route of metastatic spread. Vascular endothelial growth factor (VEGF) is a regulator of tumour angiogenesis, but studies of the inhibition of solid tumour growth by neutralizing anti-VEGF antibodies indicated that other angiogenic factors may be involved. VEGF-D may be an alternative regulator because like VEGF it is angiogenic and it activates VEGF receptor-2 (VEGFR-2), an endothelial cell receptor which is a key signalling molecule in tumour angiogenesis. This study reports the generation of monoclonal antibodies to the receptor-binding domain of VEGF-D and the use of these antibodies to localize VEGF-D in malignant melanoma. VEGF-D was detected in tumour cells and in vessels adjacent to immunopositive tumour cells, but not in vessels distant from the tumours. These findings are consistent with a model in which VEGF-D, secreted by tumour cells, activates endothelial cell receptors and thereby contributes to the regulation of tumour angiogenesis and possibly lymphangiogenesis. In addition, VEGF-D was detected in the vascular smooth muscle, but not the endothelium, of vessels in adult colon. The endothelium of these vessels was negative for VEGFR-2 and VEGFR-3. As VEGF receptors can be up-regulated on endothelium in response to vessel damage and ischaemia, these findings of a specific localization of VEGF-D in smooth muscle of the blood vessels suggest that VEGF-D produced by vascular smooth muscle could play a role in vascular repair by stimulating the proliferation of endothelial cells.     

Vascular growth factors and lymphangiogenesis

Blood and lymphatic vessels develop in a parallel, but independent manner, and together form the circulatory system allowing the passage of fluid and delivering molecules within the body. Although the lymphatic vessels were discovered already 300 years ago, at the same time as the blood circulation was described, the lymphatic system has remained relatively neglected until recently. This is in part due to the difficulties in recognizing these vessels in tissues because of a lack of specific markers. Over the past few years, several molecules expressed specifically in the lymphatic endothelial cells have been characterized, and knowledge about the lymphatic system has started to accumulate again. The vascular endothelial growth factor (VEGF) family of growth factors and receptors is involved in the development and growth of the vascular endothelial system. Two of its family members, VEGF-C and VEGF-D, regulate the lymphatic endothelial cells via their receptor VEGFR-3. With the aid of these molecules, lymphatic endothelial cells can be isolated and cultured, allowing detailed studies of the molecular properties of these cells. Also the role of the lymphatic endothelium in immune responses and certain pathological conditions can be studied in more detail, as the blood and lymphatic vessels seem to be involved in many diseases in a coordinated manner. Discoveries made so far will be helpful in the diagnosis of certain vascular tumors, in the design of specific treatments for lymphedema, and in the prevention of metastatic tumor spread via the lymphatic system.     

Correlation of vascular endothelial growth factor-D expression and VEGFR-3-positive vessel density with lymph node metastasis in gastric carcinoma

Lymph node metastasis is an important prognostic factor in gastric cancer. Vascular endothelial growth factor-D (VEGF-D) is a lymphangiogenic growth factor that activates VEGF receptor (VEGFR)-3, a receptor expressed in the lymphatic endothelium. We investigated the clinical value of VEGF-D expression and VEGFR-3 positive vessel density in gastric carcinoma with regard to lymphangiogenesis. Immunohistochemical staining was used to determine the expression of VEGF-D and VEGFR- 3 in specimens from 104 cases of resected gastric cancer. VEGF-D expression was observed in 62.5% of the gastric cancers and in 9.6% of the non-neoplastic gastric tissue. The VEGFR-3-positive vessel density was significantly greater in the VEGFD positive group than the negative group. VEGF-D expression was significantly associated with lymph node metastasis, increased serum CEA levels, and the nonsignet ring cell type. The VEGFR-3-positive vessel density was correlated with tumor size, lymphatic invasion, and lymph node metastasis. The VEGF-D expression and high VEGFR-3-positive vessel density were significant poor prognostic factors for relapse-free survival. These results suggest that VEGF-D and VEGFR-3-positive vessel density are potential molecular markers that predict lymphatic involvement in gastric carcinoma.     

Expression of vascular endothelial growth factor-C and its receptor in invasive micropapillary carcinoma of the breast

Invasion to lymphatic vessels and metastasis to lymph nodes are frequent complications in invasive micropapillary carcinoma (IMPC) of human breast cancer. Vascular endothelial growth factor-C (VEGF-C) and its receptor, VEGFR-3 have been implicated as the important factors in the formation of lymphatic vessels and recent experimental evidence strongly suggests that lymphangiogenesis in tumor promotes lymphatic metastasis. To clarify the mechanism of its occurrence, the expression of VEGF-C, VEGFR-3 and lymphatic vessel density (LVD) was examined in 40 cases of IMPC (pure and mixed type) and in 40 cases of pseudo-IMPC. Cytoplasmic expression of VEGF-C and VEGFR-3 were more frequent in tumor cells of IMPC compared to those of pseudo-IMPC. A significant positive correlation was found between the expression of VEGF-C and VEGFR-3 in both IMPC and pseudo-IMPC. The expression of VEGF-C was also significantly associated with higher peritumoral LVD, lymphatic invasion and number of lymph node metastasis in IMPC. These findings suggest that VEGF-C promotes the proliferation of peritumoral lymphatic vessels and that lymphatic invasion and metastasis to lymph nodes are frequently induced in IMPC of breast.