Immunological aspects of human implantation.

The immunological relationship between the mammalian fetus and its mother during pregnancy has been considered similar to that between a transplanted allograft and its recipient. Hence, it has been assumed that implantation of the fetal placenta in the uterus would be controlled in a similar way by a maternal immune response mediated by T cells recognizing paternally derived alloantigens expressed by the placenta. However, recent evidence indicates that implantation might involve predominantly a novel allogeneic recognition system based on natural killer cells rather than T cells. The cellular and molecular basis of this local immune interaction between the fetal placenta and maternal uterus is the focus of intense research interest. As aberrant implantation can cause a variety of clinical problems including miscarriage, intrauterine growth retardation and pre-eclampsia, an understanding of the immunological mechanism by which this process is controlled could lead to the development of regimens to improve fetal growth and development.