Immune aspects of endometriosis: relevance of the uterine mucosal immune system.

Endometriosis is classically defined as the growth of endometrial cells at sites outside the uterus. It is a common disease characterized by infertility, chronic pain and adhesion formation. Immune dysregulation, evidenced by decreased clearance of endometrial cells and aberrant production of cytokines by peritoneal fluid leukocytes, has been proposed as a mechanism which allows implantation and growth of ectopic endometrium. Cytokines are primary components of intercellular signaling between uterine epithelial and stromal cells, leukocytes, and the developing conceptus. Because their production is regulated by sex hormones, cytokines are well-placed to play a key role in the extensive tissue remodeling required to accommodate menstruation, implantation and pregnancy. Understanding this specialized hormonally-responsive mucosal immune system within the uterus will be critical to understanding the potential importance of the immune system in the pathogenesis of endometriosis. In this review, highlights of studies describing leukocyte populations, cytokines and cytokine receptors in uterine and ectopic endometrium and their proposed role in the regulation of immune processes and endometrial growth are presented, followed by a review of current data on immune aspects of endometriosis. Studies directed at investigating the hormonal regulation of cytokine secretion by uterine and peritoneal cell populations, and the effect of cytokines on endometrial proliferation, should provide a more complete understanding of their potential role in normal uterine growth and in the pathogenesis of endometriosis.