HUMAN PLACENTATION - TRANSPLANTATION OR T UMOR-MODEL

In human placentation, anchoring villi develop to attach the placenta to the wall of the uterus. This attachment is brought about by extensi ve infiltration of the maternal tissue by cytotrophoblast cells of fet al origin. As trophoblast cells do not express classical histocompatib ility antigens (HLA antigens), increasing doubt has been cast upon the ''transplantation'' model of pregnancy. However, more recently discov ered, previously unknown HLA antigens on the invasive cytotrophoblast cells could lead to maternal immune responses similar to those observe d following organ transplantation. Nevertheless, the biological behavi our of the invasive cytotrophoblast cells suggests more parallels with the processes of invasion and metastasis seen in malignant rumours, a lthough there is regulation of the timing and extent of cytotrophoblas t invasion of the uterus in normal pregnancy. In this survey, findings relating to the control of infiltration by the cytotrophoblast are re viewed, with particular reference to immunology and tumour biology. Po ssible effects on pregnancy and parturition due to failure of the regu latory processes involved in placentation are discussed.