Site-directed differences in the immune response to the fetus.

Major differences in the maternal immune response to the fetus were observed in the placentomes and in the interplacentomal regions of the pregnant sheep uterus. Firstly, fewer lymphocytes were detected in the placentomes compared to the interplacentomal regions and to non-pregnant uterine tissue (Lee, Gogolin-Ewens & Brandon, 1988). Secondly, a large population of CD45R+ granulated lymphocytes was uniformly distributed in the interplacentomal uterine epithelium throughout pregnancy but never in the syncytial layer of the placentomes. Thirdly, monoclonal antibodies specific for the CD5 antigen consistently stained the endothelium of blood vessels within the placentomes but never blood vessels in the interplacentomal areas. Finally, OLA class I antigens were present on the interplacentomal uterine epithelial cells and on the maternal stromal cells, but no staining of the trophoblast or syncytium was observed. These observations suggest that different mechanisms to prevent immune rejection of the fetus may operate in the placentomes where trophoblast invasion of the maternal tissue occurs compared to the interplacentomal regions.