Characterization of endothelial cells of lymphatic vessels

Mancardi, Sabrina (2001). Characterization of endothelial cells of lymphatic vessels. PhD thesis The Open University.



Endothelial cells form the inner lining of blood and lymphatic vessels. In mice only tumours of the blood vessel endothelium (haemangiomas) have been thus far reported. In the first part of this thesis is described a highly reproducible method for the induction of benign tumours of the lymphatic endothelial cells (lymphangioma) in mice, by intraperitoneal injection of incomplete Freund's adjuvant. Different criteria have been used in order to establish the nature of the induced lesion. Morphological and histophatological studies of the tumour developed in the peritoneal cavity revealed the presence of cells at various levels of vascular development. Expression of the endothelial markers PECAM/CD31, ICAM-l/CD54, ICAM 2/CDI02 as well as the vascular endothelial growth factor (VEGF) receptor Flk-I, the endothelial cell specific receptors Tie-I, Tie-2, and the lymphatic endothelial specific Flt-4 was identified. When the lesion was induced in ~- galactosidase knock-in Flt-4+/- mice, the tumour endothelia could be stained blue in a number of tumour cells. Tumour-derived cells were propagated in vitro where they spontaneously differentiated, forming vessel-like structures. This evidence leads to the conclusion that this is the first experimental protocol for the induction of a lymphatic endothelium hyperplasia in mice peritoneum.

The second part of this thesis describes the use of this model system to investigate the profile of chemokine expression in murine lymphangiomas and in lymphangioma-derived lymphatic endothelial primary cultures. Chemokines are a superfamily of small, secreted chemoattractant molecules that plays a key role in the immune cell trafficking. Although production of chemokines by vascular endothelial cells has been extensively documented, there is much less information regarding the lymphatic endothelium. The reported results are the first detailed analysis of chemokine production by lymphatic endothelial cells. Chemokines belonging to all three subfamilies (CXC, CC and C), were found to be expressed in lymphangioma. Among these molecules is remarkable the identification of CIO, a molecule previously identified only in the bone marrow.

The molecular as well as functional assays performed provide an indication of the signals that mediate the recruitment of leukocytes into lymphatic vessels.

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