ULTRASTRUCTURAL LOCALIZATION OF CHORIONIC GONADOTROPIN IN HUMAN TERM PLACENTA

Abstract

Human chorionic gonadotropin (HCG) was localized in human placenta at the ultrastructural level by an immunocytochemical method which linked the antigen HCG to a peroxidase label through the antigen-antibody reactions of an immunoglobulin-peroxidase bridge. Material on the maternal surface of the apical plasma membrane and in the cisternae of rough endoplasmic reticulum of the syncytiotrophoblast displayed strong immunostaining for HCG and the outer surface of the basal plasma membrane appeared equivocally immunoreactive. Lamellae and vesicles of the Golgi complex of the syncytium lacked electron-opaque reaction product indicative of immunostaining for HCG. Deposits of peroxidase reaction product in the large variety of cytoplasmic dense granule varied from negligible to abundant in immunostained and in control specimens alike and, accordingly, the large granules appeared to contain intrinsic peroxidase but not HCG. The question of the immunoreactivity of the small variety of cytoplasmic dense granule was not conclusively settled, but the occurrence of reactive and unreactive small granules in both immunostained and control specimens weighed against the presence of HCG in these rather infrequent granules. The cytotrophoblast lacked evidence of immunoreactivity.