Differences in lymphocyte-regulatory activity among variants of ovine IFN-tau

Interferon-tau (IFN-tau) is secreted from trophectoderm of the ruminant preimplantation conceptus and functions during pregnancy to prevent luteolysis. In addition, IFN-tau can inhibit proliferation of peripheral blood lymphocytes (PBL) and other cells. Several distinct ovine IFN-tau (OvIFN-tau) gene variants exist; three of these (IFN-tau4, IFN-tau6d, IFN-tau11) differ in their ability to prevent luteolysis (IFN-tau4 > IFN-tau6d > IFN-tau11), inhibit growth of Daudi cells (IFN-tau4 > IFN-tau6d > IFN-tau11), and induce an antiviral state (IFN-tau4 > IFN-tau6d = IFN-tau11). The present objective was to compare variants for differences in ability to inhibit proliferation of phytohemagglutinin-stimulated PBL. At equal concentrations, IFN-tau4 was more inhibitory than IFN-tau6d, IFN-tau11, or an IFN-omega control. Similar differences in potency were seen when IFN-tau variants were tested at equal antiviral concentrations. Thus, the sheep trophectoderm secretes variants of IFN-tau that differ in ability to regulate lymphocyte function. The nature of the effect of the trophectoderm on endometrial lymphocytes may depend on the relative amount of each variant produced.