Interferon-tau (IFN ) acts locally on the endometrium to suppress estrogen and oxytocin receptor expression and block luteolysis in ruminants. Systemic administration of conceptus homogenates or recombinant ovine IFN does not block luteolysis or enhance pregnancy rates in sheep or cattle, respectively. However, IFN up-regulates expression of the antiviral protein Mx throughout the entire uterine wall during early pregnancy. These studies determined if conceptus-derived IFN also up-regulates Mx expression in components of the circulating immune system that migrate through the endometrial wall. In experiment one, peripheral blood mononuclear cells (PBMC) were isolated from ewes at D26 post-artificial insemination (AI) and Mx mRNA levels examined by Northern and slot-blot hybridization. Pregnancy resulted in a two-fold increase in Mx mRNA levels compared to bred, non-pregnant ewes at D26. In experiment two, PBMC were isolated from ewes at AI, and every three days from D9 to D30. Results showed a four-fold increase in Mx mRNA levels in PBMC from pregnant versus bred, non-pregnant ewes at D15. Increased Mx mRNA, which remained elevated through D30, was accompanied by increased levels of Mx protein. These results show that pregnancy recognition signaling rapidly induces Mx gene expression in PBMC, and are the first to suggest that IFN activates gene expression in components of the circulating immune system.

Interferon stimulated gene 17 (ISG17) and Mx are up-regulated in the ruminant uterus in response to interferon-tau (IFN ) during early pregnancy. Recent evidence strongly indicates that expression of ISGs occur only in stroma (ST) and glandular epithelium (GE) during this time as a result of transcriptional repression by interferon regulatory factor two (IRF-2) expression in the LE. The present report tested this hypothesis by examining mRNA and protein expression of ISG17 and Mx in serial uterine cross-sections obtained from cyclic and early pregnant ewes. In situ and immunocytochemical analysis revealed that ISG17 mRNA and protein were low to undetectable, whereas Mx mRNA was expressed in the lumenal (LE) and superficial GE at all days of the estrous cycle examined. Both ISG17 and Mx mRNA increased in the stratum compactum ST between Days 11 and 13, and expression extended into the deep GE and stratum spongiosum ST on Days 15 through 17 in pregnant ewes. Interestingly the Mx gene continued to be strongly expressed in LE and superficial GE through Day 17 of pregnancy, whereas ISG17 remained low to undetectable in these cells. Collectively, this study highlights the complexity of the uterine environment by unequivocally illustrating differential temporal and spatial expression of the IFN-responsive genes ISG17 and Mx.