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