INTERFERON-TAU AND PREGNANCY

A type I interferon known as IFN-tau is expressed massively by the out er epithelium (trophectoderm) of the preimplantation trophoblast of ru minant ungulate species, such as cattle and sheep, for a few days duri ng early pregnancy. They signal to the mother that she is pregnant and indirectly prevent regression of the corpus luteum so that progestero ne production is maintained and normal ovarian cyclicity avoided. Desp ite their clear roles as reproductive hormones, the IFN-tau have the t ypical antiviral, antiproliferative, and immunomodulatory activities o f other type I IFN. They are most closely related to the 172 amino aci d IFN-omega. Unlike other type I IFN, they are not virally inducible a nd appear to be produced constitutively as the trophectoderm first for ms during the development of the blastocyst. The discovery of the IFN- tau illustrates the diverse activities of interferons and their likely involvement in the normal embryonic development of mammals. The diver sity of mechanisms different groups of mammals use to prolong the func tional life span of the corpus luteum in early pregnancy is probably t he consequence of genetic conflict between the genes of the mother and her offspring, which has led to remarkably high rates of change in pl acental structure and trophoblast signaling mechanisms.