Role of cytokines in progression of endometriosis

Peritoneal fluid in women with endometriosis contains an increased number of activated macrophages that secrete a variety of cytokines, including interleukin (IL)-6, IL-8, vascular endothelial growth factor, and tumor necrosis factor-alpha (TNF-alpha). Cytokines may be involved in the control of implantation and the growth of endometrial cells outside the uterus. In addition, several cytokines have been implicated in or directly associated with angiogenic activity in endometriosis. There could be a relationship between the levels of cytokines in the peritoneal fluid of patients with endometriosis and the status of the lesions in such patients. Peritoneal endometriosis can be classified as having red, black, or white lesions. Red lesions are known to be an active form of early endometriosis, because vascularization and mitotic activity are shown to be most prominent in these lesions. We found that the peritoneal fluid levels of TNF-alpha and IL-8 were significantly higher in patients with endometriosis, and correlated with the size and number of active lesions. In addition, TNF-alpha and IL-8 stimulated the growth of ectopic endometrial stromal cells. These cytokines with angiogenic activity may therefore have significant roles in the pathogenesis of endometriosis.