Toll-like receptor system and endometriosis.

Endometriosis is an estrogen-dependent chronic inflammatory condition associated with variable degrees of pelvic pain and infertility. Studies have showed that the growth and progression of endometriosis continue even in ovariectomized animals. This indicates that besides ovarian steroid hormones, the growth of endometriosis can be regulated by the innate immune system in the pelvic environment. As a component of innate immune system, increased infiltration of macrophages has been described in the intact tissue and peritoneal fluid of women with endometriosis. Different immune cells and dendritic cells express Toll-like receptors (TLR) and exhibit functional activity in response to microbial products. In this review article, we discuss the role of the TLR system in endometrium and endometriosis and outline the involvement of cytokines/endotoxin in causing adverse reproductive outcome. In the first part of this review article, the fundamentals of innate immune system, functional characteristics of TLR and signaling pathways of TLR4 are discussed for easy understanding by the readers.