Interferons at the placental interface

The antiluteolytic factors secreted by sheep and cattle conceptuses are closely related structurally to alpha-interferons (IFN-alpha s). They are known as ovine and bovine trophoblast protein-1 (oTP-1 and bTP-1), respectively. The mRNAs for oTP-1 and bTP-1 are transcribed from multiple genes and are the major translatable messages of Day 13-17 sheep conceptuses and Day 15-20 cattle conceptuses. The proteins belong to the 172-amino acid IFN-alpha II (or IFN-omega) subfamily and have the typical antiviral and antiproliferative properties of the 166-residue IFN-alpha Is. These embryonic interferons also bind to the IFN-alpha receptor, which is present in uterine endometrium in high concentrations, and can influence the production of prostaglandin F-2 alpha and the pattern of protein secretion in that tissue. Through use of in-situ hybridization procedures on tissue sections and Northern and dot blot analyses of extracted conceptus RNA, ovine oTP-1 mRNA has been shown to increase markedly around Day 13 and to decrease after about Day 15 of pregnancy. The mRNA is confined entirely to cells of the trophectoderm. Significant induction of mRNA that hybridizes to an oTP-1 cDNA occurs in response to exposure to polyI:polyC in Day 11 sheep blastocysts which normally have low levels of oTP-1 expression. However, the basis for induction in the normal progression of embryonic development remains unclear. The fact that preimplantation conceptuses of other species, e.g. pig, release substances with antiviral activity suggests that IFNs may have an important role in pregnancy that extends beyond the domestic ruminants.