Distinct molecular composition of blood and lymphatic vascular endothelial cell junctions establishes specific functional barriers within the peripheral lymph node

Lymph nodes are strategically localized at the interfaces between the blood and lymphatic vascular system, delivering immune cells and antigens to the lymph node. As cellular junctions of endothelial cells actively regulate vascular permeability and cell traffic, we have investigated their molecular composition by performing an extensive immunofluorescence study for adherens and tight junction molecules, including vascular endothelium (VE)-cadherin, the vascular claudins 1, 3, 5 and 12, occludin, members of the junctional adhesion molecule family plus endothelial cell-selective adhesion molecule (ESAM)-1, platelet endothelial cell adhesion molecule-1, ZO-1 and ZO-2. We found that junctions of high endothelial venules (HEV), which serve as entry site for naive lymphocytes, are unique due to their lack of the endothelial cell-specific claudin-5. LYVE-1(+) sinus-lining endothelial cells form a diffusion barrier for soluble molecules that arrive at the afferent lymph and use claudin-5 and ESAM-1 to establish characteristic tight junctions. Analysis of the spatial relationship between the different vascular compartments revealed that HEV extend beyond the paracortex into the medullary sinuses, where they are protected from direct contact with the lymph by sinus-lining endothelial cells. The specific molecular architecture of cellular junctions present in blood and lymphatic vessel endothelium in peripheral lymph nodes establishes distinct barriers controlling the distribution of antigens and immune cells within this tissue.

Vascular endothelial growth factors, angiogenesis, and survival in human ileal enterochromaffin cell carcinoids

BACKGROUND AND AIMS: Well-differentiated neuro-endocrine ileal carcinoids are composed of serotonin-producing enterochromaffin (EC) cells. Life expectancy is determined by metastatic spread to the liver because medical treatment options are still very limited. Selective inhibition of angiogenesis or lymphangiogenesis might prevent tumour growth and metastatic spread. We examined the role of the vascular endothelial growth factors (VEGFs) A, B, C, D, and their receptors (VEGFRs) 1, 2, 3 in angiogenesis and lymphangiogenesis of ileal EC cell carcinoids with and without liver metastases. METHODS: The expression of various VEGFs and VEGFRs was determined by quantitative real-time RT-PCR in healthy mucosa, primary tumour, lymph node metastases and liver metastases of 25 patients with ileal EC cell carcinoids. Microvessel density (MVD) was determined by CD-31 staining in primary tumours and lymphatic vessel density (LVD) by LYVE-1 staining. VEGF expression levels, MVD, LVD, and patients' survival time were correlated using logistic regression and Kaplan-Meier survival analysis. RESULTS: VEGF-A was highly expressed with no difference between normal mucosa and tumours. VEGF-B and -D as well as VEGFR-1 and -2 expression levels were significantly increased in the tumours when compared to normal mucosa. Patients with liver metastasis, however, had a significantly lower expression of the factors A, B, and C and the receptors 2 and 3. MVD in primary tumours positively correlated with the expression of VEGF ligands and their receptors, except for VEGF-D. LVD did not correlate with any VEGF ligand or receptor. Interestingly, low expression levels of VEGF-B were associated with poor survival. CONCLUSION: Patients with more aggressive metastatic spreading had relatively decreased expression levels of VEGF ligands and receptors. Thus, anti-angiogenic therapy may not be a suitable target in metastatic ileal EC cell carcinoids.