Trophoblast interferons in early pregnancy of domestic ruminants.

A type I interferon (IFN) secreted by the trophoblast of early sheep and cow embryos is thought to be responsible for the maternal recognition of pregnancy. The expression of trophoblast IFN is tissue specific and temporally controlled. However, the isolated bovine trophoblast IFN promoter did not confer tissue specificity on the expression of a bacterial chloramphenicol acetyl transferase (CAT) reporter gene, and could not be induced by virus, unlike other type I IFNs. Trophoblast IFN acts locally within the uterus to prevent luteolysis and prolong progesterone secretion. Endometrial IFN receptors are present, and trophoblast IFN decreases expression of endometrial oxytocin receptor and increases expression of endometrial beta 2-microglobulin, MHC class I antigens and Mx (a mediator of IFN antiviral activity) only in the pregnant horn of pregnant ewes with a transected uterus. The primary effect of trophoblast IFN during early pregnancy appears to be an inhibition of oxytocin receptor expression, although studies in ovariectomized ewes suggest that luteal oxytocin may be required to facilitate the inhibition of prostaglandin F secretion by trophoblast IFN. An investigation of the isolated oxytocin receptor promoter should confirm its critical role in the maternal recognition of pregnancy.