It was interesting to note that p3, as well as its truncated counterpart, were at least 200-fold more potent in antiproliferative activity than were ovine and bovine IFN-ts tested previously. Their activities approached those of huIFN-a2 and huIFN-w in the same assay, presumably because ovIFN-т-рЗ possesses a much higher affinity for the human type I IFN receptors than do other IFN-ts. However, binding constants for ovIFN-ts on human cells have not been defined. The slight, but significant, increase in antiproliferative activity of the truncated form of ovIFN-t p3 suggests that the 3-nm tail might interfere with binding to the human receptor or destabilize the complex in some way. flovent inhaler
Serum progesterone concentrations above 1 ng/ml have previously been maintained in ewes with as little as 100 (xg/day of either conceptus-derived or recombinant ovIFN-т. Extensions of CL function have also been induced in cattle by conceptus-derived and recombinant boIFN-т in amounts as low as 70 (xg/day and 200 (xg/day, respectively. In the present study, 60 (xg/day of either p3 or its truncated counterpart provided a dose effective for luteal maintenance in ewes. In addition, the extension in luteal function was sufficient to alter uterine physiology to a state similar to that during pregnancy, as expression of uterine serpin was induced in ewes with extended luteal life spans. These quantities of IFN-т are well within the range of the estimated daily amounts secreted by ovine concep-tuses in culture during peak IFN-т production and should be considered physiological. In this and earlier studies, CL life span was extended well beyond the time that the endometrium was exposed to IFN-т. In sheep, this period of pseudopregnancy can last for several weeks, although only rarely does it approach that of a normal gestation. In cattle, by contrast, IFN-т treatment rarely provides an extension of more than 10 days. Why such a species difference occurs is unclear.