Toll-like receptors and pregnancy: trophoblast as modulators of the immune response.

During normal pregnancy, the decidua is populated by a variety of leucocytes; however, cells of the innate immune system seem to dominate this tissue. Their presence suggests that the innate immune system is not indifferent to the fetus and has been associated with a response of the maternal immune system to the 'semi-allograft' fetus. New evidences, however, indicate that these immune cells are critical for decidual and trophoblast development rather than induction of tolerance. We hypothesized that during implantation, an inflammatory environment is necessary for the attachment and invasion of the blastocyst. The existence of an 'inflammatory-mediated embryo implantation' condition is dependent on the proper 'education' of the innate immune system which we propose is mediated by the trophoblast. Here we postulate that trophoblast cells successfully orchestrate their inflammatory environment and regulate immune cells differentiation and activation through Toll-like receptors (TLR). We will describe potential functions of TLR in trophoblast cells, their recognition and response to microorganisms, and their involvement in innate immunity.