Cytokines in implantation

The endometrium of most species is now recognized as an important site of p roduction of cytokines and their receptors. The cellular origin of the cyto kines varies but many predominate in the uterine glandular or luminal epith elium or in the decidualized stromal cells. From studies in genetically mod ified mice if is clear that implantation of the blastocyst can proceed in t he absence of most individual cytokines, although leukemia inhibitory facto r and interleukin-ll have indisputable roles in this process. In other case s, such as CSF-I, GM-CSF, IL-I, and IL-6, the numbers of implantation sites or litter sizes are reduced when the cytokine is absent. The same cytokine s that are implicated in implantation in mice are generally maximally expre ssed in human endometrium with maximal production in the secretory phase, p articularly during the "window of implantation," but functional studies of their role in implantation in women and other primates are still required.