Toll-Like Receptor System in the Human Endometrium

The mucosal surface of the uterine cavity is a complex biosystem, which provides a barrier against the outside world and participates in both innate and acquired immune defense systems. This mucosal compartment has adapted to a dynamic, non-sterile environment challenged by a variety of antigenic/inflammatory stimuli associated with sexual intercourse and endogenous vaginal microbiota. Thus, the epithelial cells, fibroblasts, lymphocytes, macrophages, and dendritic cells associated with the human endometrium possess unique features that enable them to adapt to this dynamic milieu. Rapid innate immune defenses against microbial infection usually involve the recognition of invading pathogens by specific pattern-recognition receptors recently attributed to the family of Tolllike receptors (TLRs). TLRs recognize conserved pathogen-associated molecular patterns (PAMPs) synthesized by microorganisms, but not by the host. Members of the TLR family, which includes 10 human TLRs identified to date, recognize distinct PAMPs produced by various bacterial, fungal, and viral pathogens. The available literature regarding the innate immune system of the endometrium during human reproductive processes was reviewed in order to identify studies specifically related to the expression and function of TLRs under normal as well as pathological conditions. Increased understanding of these molecules in the endometrium may provide insight into site-specific immunoregulatory mechanisms in the female reproductive tract.