Comparative studies on the distribution of binucleate cells in the placentae of the deer and cow using the monoclonal antibody, SBU-3.

A monoclonal antibody SBU-3 raised against an antigen expressed by the binucleate cells in the trophoblast of the sheep placentome crossreacts with an antigen expressed by binucleate cells in the placenta of the deer and the cow. This monoclonal antibody has been used to study the distribution of this subpopulation of binucleate cells in the deer and cow during fetal development. In the deer at less than 30 days of gestation, SBU-3-positive binucleate cells were observed in the trophoblast of the chorionic villi and in the trophoblast at the interplacentomal areas. With the advancement of pregnancy, the placentome increased in size and SBU-3-positive binucleate cells were observed to localise mainly at the tips of the chorionic villi and were arranged in clusters. There was evidence of SBU-3-positive binucleate cell migration into the epithelium of the caruncular crypt, but there was no fusion of migrated cells to form a syncytial layer. Such a pattern of SBU-3-positive cell distribution was seen up to 95 days of gestation, the oldest placenta available for study. In the cow at 28-34 days of gestation, SBU-3-positive binucleate cells were seen in the trophoblast located in close apposition to the caruncular epithelium. From 35-240 days, there was an increase in the number of SBU-3-positive binucleate cells in the placentomal trophoblast. As in the deer, SBU-3-positive binucleate cells migrated into the epithelium of the caruncular crypt, and these cells did not fuse to form a syncytial layer. By 241-283 days, SBU-3-positive binucleate cells present in the placentomal trophoblast were stained less intensely. Many of the binucleate cells which had migrated into the epithelium of the caruncular crypts had pyknotic nuclei and scanty cytoplasm containing weakly stained SBU-3-positive product. It is concluded that the monoclonal antibody SBU-3 recognises an antigen common to ruminants which is expressed only by binucleate cells in the placenta. In the deer and the cow, granule transfer seems to be the primary function of binucleate cell migration. The histological classification of the mature placenta of the deer and the cow is epitheliochorial.