Abstract
The localization of human placental alkaline phosphatase (HPALP) was demonstrated by both conventional enzyme-histochemistry and immuno-histochemistry of the indirect peroxidase-labeled antibody method at light and electron microscopic levels. The location of the HPALP was exclusively confined to the microvilli of syncytiotrophoblastic cells by both methods. In early gestational ages, the distribution of the enzyme reaction positive villi was not uniform. At full term, all the syncytiotrophoblastic cells of chorionic villi uniformly showed the most intense staining for the alkaline phosphatase. On tissue sections of the chorionic villi, the HPALP was distinguished from the isoenzymes of small intestine and kidney by the bio-, physico- and immunochemical properties, e.g.: the sensitivity to the stereospecific inhibitor, the L-phenylalanine (0.05M), heat stability (65°C), and the specific reactivity to the anti-HPALP. The specificity and validity of the immunohistochemical staining at the surfaces of the chorionic villi, especially at an ultrastructural level, are throughly discussed. It is suggestive of the usefulness of this im-munohistochemical staining method for the investigation of Megan type isoenzyme produced in certain malignant tumors.
