The present study lends support to our previous hypothesis built on data obtained with in vitro experiments, that IFN-т stimulates both COX-2 and GM-CSF in the endometrium. However, a few differences were observed. In vitro, IFN-т induced the expression of COX-2 in both epithelial and stromal cells and up-regulated GM-CSF in stromal cells and leukocytes.
In vivo, the effect on immune cells could not be verified because their GM-CSF expression was not intense enough to allow exact discrimination between intraepithelial leukocytes and epithelial cells and between stromal leukocytes and capillaries or fibroblasts. On the other hand, the expression pattern of the two proteins in the LE in vivo followed the window of IFN-т synthesis and contrasted with an absence of correlation in the stroma. Moreover, in cows treated with IFN-т, COX-2 and GM-CSF were increased only in the LE, not in the stroma. These differences could be explained in part because, usually, epithelial and stromal cells are cultured separately in vitro, whereas they are free to interact in vivo where the LE is also exposed to higher concentrations of mediators from the conceptus, compared with the stroma.