Abstract
Human chorionic gonadotropin (HCG) was proved to exist on the cell surface of a syncytiotrophoblast by the immuno-electron microscopic technique. The cell surface, including microvilli and micropinocytosis vesicles, was positive. Two types of HCG were observed; one loosely and the other tightly connected to the cell surface. The latter was closely related to the acid mucopolysaccharide of the cell surface coat, revealed by ruthenium red staining. These ultrastructural findings suggest that HCG acts as a local immunosuppressant on the syncytiotrophoblast cell surface, preventing partial maternal immunological reactions against the fetus.
