An ultrastructural study of alkaline phosphatase activity in normal and neoplastic human salivary glands

Alkaline phosphatase activity of normal human parotid and submandibular glands and four benign mixed tumours of the parotid gland was investigated by ultrastructural cytochemistry in order to identify myoepithelial cells and the extent of their participation in the histogenesis of such tumours. The results indicated that myoepithelial cells in the normal salivary glands were negative for alkaline phosphatase activity and, therefore, enzyme localization as a marker for identification of such cells in mixed tumours was not reliable. Occasional neoplastic cells in the more glandular parts of the tumours displayed surface membrane associated alkaline phosphatase reactivity. In addition, the luminal microvilli of some neoplastic cells were positive for the enzyme, thereby suggesting a resorptive or absorptive function for cells which were formerly secretory in nature.