Enzyme-histochemical method for identification of lymphatic capillaries.

Using 5'-nucleotidase (5'-Nase)-alkaline phosphatase (ALPase) double staining, lymphatic capillaries and blood capillaries were distinguished histochemically on cold glycol methacrylate (JB-4) sections of monkey intestines, on the basis of both enzyme characteristics. The specificity of the 5'-Nase reaction was obtained by inhibiting nonspecific ALPase in the 5'-Nase incubation medium including L-tetramisole. This double staining method demonstrated satisfactory isolated visualization of 5'-Nase activity in lymphatic capillaries and of ALPase activity in blood capillaries under light microscopy. The intensity and localization of 5'-Nase activity on the walls of lymphatic capillaries were also determined by the lead-based method under transmission electron microscopy. The intense reaction products of 5'-Nase activity were predominantly deposited on the outer surface of the plasma membrane of the lymphatic endothelial cells.