Distribution of Human Placental Antigens and their Age-Associated Changes

Abstract

To study the correlation between the development of placenta and its functional changes, immunoflourescent and immuno-histochemical analyses of the distribution of cell- surface antigens of chorionic cells and their age-associated changes were performed, using placentas ranging from 5 gestational weeks to the period of delivery. Monoclonal antibody (MAb) Trop 1 which had been raised against the human chori ocarcinoma cell-line BeWo, reacted with cytotrophoblast, but not with syncytiotrophoblast and non-villous trophoblast, in the first trimester. However, this antigen gradually disappeared after 16 gestational weeks and was negative on the cytotrophoblast of the placentas more than 28 gestational weeks. A very weak expression of Trop 1 was noted on the cytotrophoblast in the case oh intra-uterine fetal death which occurred before 16 gestational weeks. Therefore, Trop 1 seems to be an important functional molecule on the cytotrophoblast at an early phase of pregnancy. The stromal Hofbauer cells (placental macrophages) were also positive for Trop 1. These cells were distinguished by thier morphological characteristics and the expression of HLA class I, HLA-DR and LeuM 3 antigens. Trop 2 antigen, the antigen detected by another MAb raised against BeWo cells, was also distributed only on the cytotrophoblast. The expression of this antigen did not change during the development of the placenta. In contrast to Trop 1 and Trop 2 the transferrin receptor was located on syncytiotrophoblast and partially on the non-villous trophoblast, and was expressed throughout the pregnancy. Thus, this molecule appears to play a role in the basic metabolism of the placenta throughout the pregnancy. Studies of HLA antigens showed that both Class I and Class II antigens were not expressied on the chorionic villous epithels. However, the Class I antigen was positive on the non-villous trophoblast. The lack of HLA antigens on the villous trophoblasts appears to be advantageous against the maternal immune response to the fetus.