Part J: Placental Interferons, Implantation and Pregnancy

Interferons have antiviral, antiproliferative and immunomodulatory effects on immune responses to defend the body against viral infections and malignant cells. The type I interferon family includes interferons alpha (IFNA1-IFNA10, IFNA13, IFNA14, IFNA16, IFNA17 and IFNA21), interferon beta (IFNB), interferon delta (IFND), interferon epsilon (IFNE), interferon kappa (IFNK), interferon tau (IFNT) and interferon omega (IFNW1-IFNW3). Interferon gamma (IFNG) is the only known type II interferon. Of the type I interferons, IFNT is expressed by mononuclear trophectoderm cells of ruminant conceptuses and IFND is expressed by equine and porcine conceptuses to affect pregnancy recognition and the uterine environment at the peri-implantation stage.

The pig conceptus also secretes IFNG during the peri-implantation period, but its role is not known. It is clear that interferons secreted by conceptus trophectoderm and/or immune cells recruited to the site of implantation of blastocysts during early pregnancy affect mechanisms for establishing the window of implantation as well as uterine acceptance of the conceptus, and placentation in many, if not all, species of mammals. This conserved trait of the mammalian peri-implantation period involves secretion of type I and/or a type II IFNs by trophectoderm cells which induces and/or enhances the expression of interferon stimulated genes in a cell-specific (spatial) fashion. Ruminant IFNT is the sole interferon so far identified as a signal of early pregnancy. But interferons produced by the conceptus or uterine immune cells of other species likely affect the peri-implantation uterus as well as endometrial decidualisation, and placental growth and development critical to successful outcomes of pregnancy. This review will highlight current knowledge of interferons that may affect pregnancy outcomes in humans, domestic animals and rodents.

Keywords: Interferons, pregnancy, uterus, implantation, placentation.