Uterine monocytes and macrophages: New insight into their pivotal homeostatic inflammatory role during reproductive life.

The repeated (menstrual) cycles of tissue proliferation, differentiation, degradation and shedding in the lining of the uterus (endometrium) make this arguably the most dynamic tissue of the body in the steady state. Many of the tissue processes involved resemble those occurring during wound repair, in which there is a wealth of knowledge regarding the contributions of macrophages to tissue remodelling in other tissues. In addition, several inflammatory events also regulate tissue integrity in the uterus including apoptosis, alongside numerous inflammatory myeloid-specific cytokines peaking during the window for embryo implantation. We discuss the key roles that both monocytes and the macrophages that they differentiate into play in regulating tissue integrity in the uterus during the menstrual cycle, and the relevance to reproductive physiology. We describe inflammatory and repair processes, which monocyte or macrophage subsets may be responsible, and at which point of the menstrual cycle. An understanding of macrophage biology in the uterus and their contributions to tissue physiology is essential for understanding the pathophysiology of reproductive diseases that contribute to infertility and pregnancy complications.