Bioscientifica Proceedings

In several ungulate species, the preimplantation trophoblast, among various secretions, produces large amounts of antiviral activity that was identified as interferon (IFN). IFNs (types I and II) are pleiotropic cytokines, which in addition to a potent antiviral activity, exert multiple effects on cell growth and differentiation, in particular on the cells of the immune system. In ruminants, trophoblastic IFN, or trophoblast protein-1 (TF-1), was found to consist of a multigenic family related to type I IFN-ω These IFNs exert hormone-like effects through receptors present on the endometrium, leading to the prolongation of luteal lifespan and hence to sustained progesterone secretion. In pigs, a species in which the maternal recognition of pregnancy is controlled by conceptus-derived oestrogens, two IFNs have been found in the preimplantation trophoblast. The major species is IFN-γ (type II), that so far had been found only in activated T lymphocytes and natural killer (NK) cells. Transcription of the IFN-γ gene in the pig trophoblast differs from that in mature lymphocytes, since two mRNAs are present. The other component with antiviral activity is a novel type I IFN; distant in sequence from IFN-α, β, ω, and containing seven cysteines in its deduced mature protein. These two unrelated IFNs are temporally co-induced, with maximal secretion at day 16 of pregnancy. Specific receptors for both IFNs have been found on endometrial epithelial cells, but not on the preimplantation trophoblast, suggesting a paracrine effect on the uterus. Different hypotheses as to their role(s) in the establishment or maintenance of implantation are discussed. Whereas an indirect anti-infectious (antiviral) protection of the conceptus by IFNs cannot be ruled out, arguments are presented that do not favour a role in the immune tolerance of the conceptus.

© 1993 Journals of Reproduction & Fertility Ltd