Immunoelectron microscopic study of PECAM-1 expression on lymphatic endothelium of the human tongue

The expression of platelet-endothelial cell adhesion molecule-1 (PECAM-1) o n lymphatic and blood vessels of the human tongue was examined with fluores cence and transmission electron microscopy (TEM), The study used anti-desmo plakins antiserum for light microscopic identification of the lymphatic ves sels, plus a pre-embedding immunogold electron microscopic technique for TE M observations. Before making TEM observations, cryostat serial sections we re immunostained with anti-desmoplakins or anti-PECAM-l and then embedded. Semithin sections from each cryostat section were photographed under a ligh t microscope and compared in order to identify the lymphatic vessels expres sing PECAM-1. In fluorescence microscopy, PECAM-1 expression on lymphatic v essels was weaker than that on blood vessels, TEM observations showed that PECAM-1 expression on the blood vessels was observed only on the luminal su rface of the endothelium. In lymphatic vessels, PECAM-1 expression was foun d both on the luminal and abluminal surfaces of the endothelium. The densit y of the PECAM-1 reaction products was lower in lymphatic vessels than in b lood vessels. The density of PECAM-1 reaction products on the luminal surfa ce of lymphatic vessels was higher than on the abluminal surfaces. The resu lts suggest that blood vessels are more active than lymphatic vessels in le ukocyte migration. The expression of PECAM-1 on the abluminal surface of ly mphatic endothelium may allow leukocytes to adhere to the endothelium and i nteract in their migration from tissue into lymphatic vessels. (C) 2001 Har court Publishers Ltd.