Expression of interferon receptor subunits, IFNAR1 and IFNAR2, in the ovine uterus.

Interferon-tau (IFN-tau) is the antiluteolytic factor released by concepti of ruminant ungulate species prior to implantation. All type I interferons, including IFN-tau, exert their action through a common receptor, which consists of two subunits, IFNAR1 and IFNAR2c, but the distribution of the two polypeptides in uterine endometrium has not been examined. In situ hybridization and immunohistochemistry on sections from pregnant and nonpregnant ovine uteri at Days 14 and 15 after estrus and mating showed that both IFNAR1 and IFNAR2 mRNA and protein were strongly expressed in endometrial luminal epithelium (LE), superficial glandular epithelium (GE), and stromal cells, within but not outside caruncles. Similar staining patterns were noted in pregnant and nonpregnant uteri for both subunits. Western blot analysis of membrane fractions from cell lines derived from endometrial LE, GE, and stromal cells, and affinity cross-linking experiments with radioactively labeled IFN-tau performed on crude endometrial membranes indicated the presence of both high ( approximately 110 kDa) and low (75-80 kDa) molecular mass forms of the two receptor subunits. To localize where IFN-tau binds when it is introduced into the uterine lumen, immunohistochemistry with an antiserum against IFN-tau was performed on sections of uteri from Day 14 nonpregnant ewes whose uteri had previously been infused with IFN-tau. Staining was concentrated on the LE and superficial GE cells, and was absent from the deeper regions of the glands and from the stromal tissues. These studies demonstrate the heavy concentration of IFNAR1 and IFNAR2 in cells of the LE and superficial GE, which appear to be the main targets for IFN-tau.