An immunohistochemical study of a series of plasma proteins in the early human conceptus.

A 20-day-old human conceptus was studied by the indirect immunoperoxidase technique for the presence of a series of plasma proteins: prealbumin (PA), albumin (ALB), alpha-fetoprotein (AFP), alpha 1-antitrypsin (A1AT), carcioembryonic antigen (CEA), immunoglobulin G (IgG), ferritin (FER), transferrin (TR), fetal haemoglobin (HbF), human chorionic gonadotropin (HCG), human placental lactogen (HPL) and pregnancy specific beta 1-glycoprotein (SP1). In the embryo only FER and TR were found. The yolk sac was positively stained for several proteins: PA, ALB, AFP, A1AT, IgG, FER, TR and HbF were demonstrated in the endodermal cells and PA, ALB, IgG and TR in the mesothelial cells. The syncytiotrophoblast of the chorionic villi were heavily stained for all the placental proteins. HCG and HPL were additionally demonstrated in the cytotrophoblast. The Hofbauer cells of the chorionic and villous stroma stained positively for A1AT and FER. TR appeared as a characteristic band on the apical surface of the syncytiotrophoblast. The findings indicate that the yolk sac is the principle source of some of the plasma proteins also in the very early conceptus and the assumption that the yolk sac is the functional antecedent of the liver is supported. The distribution of the various placental proteins is in accordance with the present knowledge that the syncytiotrophoblast is the major site of synthesis of these proteins. Finally correlation of functional aspects of embryonic structures and germ cell tumours is recommended.