However, COX-2 itself does not discriminate between PGF2a and PGE2 because it catalyzes the transformation of arachidonic acid into the same precursor for both PGF2a and PGE2, PGH2, which is rapidly converted by PGF-synthase or PGE-synthase, among others. It is notable that in many species, endometrial expression of COX-2 is stimulated during the attachment period. Granulocyte-mac-rophage colony-stimulating factor (GM-CSF) is another important factor expressed in the uterine epithelium of the mouse, human, and ruminants because it is known to promote the survival and growth of embryos in these species.
We have previously demonstrated, with cultured bovine endometrial cells and lymphocytes, that IFN-т or PGE2 enhance the secretion of PGE2 via COX-2 stimulation and the expression of GM-CSF. In the present study, immunohistochemistry (IHC) was used to localize both COX-2 and GM-CSF in the bovine endometrium. Regulation of these two proteins during the estrous cycle and early pregnancy, and after intrauterine infusions of IFN-т, was assessed by image analysis. The results suggest that the conceptus, via its production of IFN-т, up-regulates COX-2 and GM-CSF during the peri-implantation period, thus delaying luteolysis and redirecting the maternal response to its advantage, favoring its own growth and escaping immune rejection.