IFN-tau: A novel subtype I IFN1. Structural characteristics, non-ubiquitous expression, structure-function relationships, a pregnancy hormonal embryonic signal and cross-species therapeutic potentialities

IFN-tau (IFN-tau) constitutes a new class of type I IFN which is not virus- inducible, unlike IFN-alpha and IFN-beta, but is constitutively produced by the trophectoderm of the luminant conceptus during a very short period in early pregnancy. It plays a pivotal role in the mechanisms of maternal reco gnition of pregnancy in ruminants and it displays high antiviral and antipr oliferative activities across species with a prominent lack of cytotoxicity at high concentrations in vitro in cell culture and possibly in vivo. It e xhibits high antiretroviral activity against HIV and exhibits immunosuppres sive activity in a multiple sclerosis model and reduces embryo and fetal mo rtality by stimulation of IL-10 production. In this review all the biochemi cal and para-hormonal properties of this novel IFN-tau are described in det ail: structural characteristics of proteins and genes, trophoblast expressi on, regulation of its expression, structure of its gene promoter, its absen ce in human species and in non-ruminant animals, the evolution of the IFN-t au genes, its structure-function relationships with its three-dimensional s tructure, structural localization of biological activities, its lack of cyt otoxicity and its receptor. Surprisingly, for an IFN, IFN-tau is also a pre gnancy-embryonic signal with paracrine antiluteolytic activity. In order to maintain luteal progesterone secretion, IFN-tau inhibits PGF-2 alpha pulsa tile secretion and oxytocin uterine receptivity in early pregnancy. It is b elieved to suppress pulsatile release of endometrial PGF-2 alpha by prevent ing oxytocin and estrogen receptor expression. Additionally, it directly re gulates prostaglandin metabolism and possibly the PGE:PGF-2 alpha ratio. (C ) Societe francaise de biochimie et biologie moleculaire/Elsevier, Paris.