Immunocytochemical localization of human choriogonadotropin in human malignant trophoblast. Model for human choriogonadotropin secretion.

Human choriogonadotropin (HCG) and its subunits have been studied immunocytochemically using a recently developed unlabeled antibody method. Factors influencing the antigenicity of HCG and its subunits were explored, and optimum conditions were determined. HCG has been successfully localized at the cellular level using paraffin-embedded tissues. Several antibodies to HCG or its subunits were evaluated for specificity using rigorous immunologic controls. This methodology was applied to placental tissue, in vitro choriocarcinoma, and in vitro breast carcinoma. HCGbeta and HCGalpha were localized in the syncytial trophoblast of first trimester placenta with cytotrophoblast cell islands and Langhans' cells being negative. Conditions of stimulated and unstimulated HCG production have been explored in the BeWo line of malignant trophoblast. Stimulation was accomplished by treatment with dibutyryl cyclic AMP and theophylline for varying periods of time. Only 6 per cent of the cells could be shown to be producing HCGbeta and HCGalpha in the unstimulated condition. Stimulation increased this percentage to 70 and 18 per cent, respectively, after 24 hours of treatment. Ultrastructural localization has shown that the mechanism of synthesis and secretion of HCG follows a pathway that is not as extensively developed as that of the pituitary hormones.