Morphological analysis of the intracolonic lymphatic vessels with reference to the mechanism of lymphatic metastasis

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Previously, we investigated the fine structure and distribution of the lymphatic networks in several mammalian tissues using an enzyme-histochemical method with 5'-nucleotidase (5'-Nase) -alkaline phosphatase (ALPase) double staining to distinguish lymphatics and blood capillaries. Our new histochemical technique clearly demonstrated precise distribution of the lymphatic networks.In the present study, the fine distribution and structure of intramucosal lymphatics in the colon of the Japanese monkey (Macacafuscata) and human were examined mainly enzyme-histochemically with light and electron microscopy. Whole mount preparations of each tissue layer pealed from the colonic wall and cryostat sections were stained with 5'-Nase-ALPase double staining and immunostaining (LYVE-.1, D2-40).5'-Nase-positive lymphatics appeared extensive networks in the lamina propria mucosae (LPM), lamina submucosae (MS), muscularis propria (MP) and subserosal layers, and some of them were found to be closely as … More sociated with ALPase-positive blood vessels. Double-layered lymphatic networks were locally observed near the inner and outer surfaces of lamina muscularis mucosae (LMM). Numerous slender lymphatics without valve-like structures which coursed vertically, were seen in the intercryptal region. All the lymphatics were originated from horizontal networks in the deep LPM. In general, they had scarcely any communicating branch in the superficial layer of LPM except in the cecum and recto-sigmoid colon. In the cecum and recto-sigmoid colon, fine dense lymphatic networks were locally observed in the most superficial layer of LPM. On the other hand, lymphatic networks of the deep LPM were characterized by a regular mesh-like network on a basis of the penetrating point on the LMM. These lymphatic networks closely communicated with a irregular horizontal one which consisted of tubulo-saccular lymphatics and directly located under the LMM via the penetrating branch. The latter showed a lymphatic network with obvious valve-like structures and had numerous enlarged blind-endings.The present study has first demonstrated enzyme-histochemically the precise distribution of 5'-Nase-positive and/or LYVE-1 -positive initial lymphatics by using whole mount preparations in the laminar layer of the monkey and human colons. Our findings suggest that rich initial lymphatics in LPM may play an important role in absorption of the tissue fluid and various free cells. Less