The usefulness of immunostaining with anti-desmoplakin antibody for light microscopic identification of lymphatic vessels was examined in cryostat sections of the human tongue. The results were compared with laminin, 5'-nucleotidase (5'-Nase), and factor VIII staining. Immunoelectron microscopic observation was also performed to confirm that the vessels reacting with anti-desmoplakin were lymphatic vessels. Under the immunoelectron microscopic, the vessels reacting with anti-desmoplakin showed ultrastructural features characteristic of lymphatic vessels: thin endothelial walls, no or incomplete basal lamina, open junctions, and overlapping endothelium. In general, lymphatic vessels identified by anti-desmoplakin reacted strongly with 5'-Nase, but showed weak or no reactivity with anti-laminin and anti-factor VIII. Blood vessels showed no reactivity with anti-desmoplakin, but reacted strongly with anti-laminin and anti-factor VIII. However, some blood and lymphatic vessels showed intermediate reactivity with anti-laminin, anti-factor VIII, and 5'-Nase. It was difficult to identify these as blood or lymphatic vessels only by the reactivity differences. The results indicate that anti-desmoplakin antibody specifically distinguishes lymphatic vessels and is useful for studying the fine distribution of lymphatic vessels under light microscopy. (C) 2000 Academic Press.