Lymphatic network and lymphangiogenesis in the gastric wall.

A family of growth factors highly specific for endothelial cells was identified more than 10 years ago, in which the receptor of vascular endothelial growth factor C (VEGFR-3) is implicated in the regulation of lymphatic development and regeneration. Comparative studies on the lymphatic network and lymphangiogenesis have been done mainly using combined 5'-nucleotidase (5'-Nase) enzyme and VEGFR-3 immunohistochemical approaches in adult and fetal gastric walls. Developing lymphatic networks represented fewer blind ends and branches than mature networks in whole-mount preparations. Many circular lymphatic-like structures exhibited VEGFR-3 expression and weak 5'-Nase activity in the early embryonic stage, showing visible morphological properties in the lymphatic endothelium. These newly formed lymphatics showed an obvious accumulation in the submucosa and serosa and a variation in the intensity of VEGFR-3 binding to endothelial cells among samples. A reaction product for anti-VEGFR-3 was found on the luminal surface of endothelial cells and on the membrane of some organelles and intraluminal lymphocytes. These findings indicate that an active proliferating feature of the clustered developing lymphatics may create a favorable environment for their sprouting and growth, which may serve as a functional requirement for lymph drainage in the region.