MATERNAL RECOGNITION OF PREGNANCY

Maternal recognition of pregnancy reflects the various ways in which t he mother responds to the presence of a conceptus within her reproduct ive tract. A part of the biochemical information she senses may be irr elevant to pregnancy outcome, but some reflects the attempts by the co nceptus to gain some measure of control over corpus luteum function, u terine blood supply, the mother's immune system, and other aspects of maternal physiology. Most probably as a result of ongoing genetic conf lict between the mother and the conceptus, a bewildering range of plac ental structures and trophoblast signaling mechanisms are encountered in eutherian mammals despite the fact that the uterus and conceptus sh are a common interest, which is the successful outcome of the pregnanc y. Here we review some of the ways that such mammals maintain luteal f unction in early pregnancy and briefly discuss the related topics of e mbryonic loss and maternal monitoring of conceptus fitness. We next ad dress the view that the conceptus is an intruder, recognized as foreig n by the mother, that likely survives by using strategies analogous to those employed by successful parasites. In this context, we describe the pregnancy-associated glycoproteins, multiple isoforms of which are released at the trophoblast-endometrial interface during pregnancy of ungulate species. These molecules, which are structurally related to pepsin, are proposed to bind and sequester antigenic peptides, thereby serving an immunoprotective role.