Toll-like receptor-2 expression in normal and pathologic human placenta.

Toll-like receptors (TLRs) are important components of the innate immune system and are expressed by trophoblast in normal full-term placenta. At present, not much is known about the role of TLRs during normal pregnancy and in pregnancy complicated by infection. In this study, we have used immunohistochemistry to investigate the expression of TLR2 in 58 placentas from second and third trimester with chorioamnionitis and 25 full-term placentas from uncomplicated pregnancies without chorioamnionitis. TLR2 was found to be localized to the cyto- and syncytio-trophoblast cell layer and to decidual stromal cells. The expression of TLR2 in placentas with chorioamnionitis was significantly lower than in placentas without chorioamnionitis. Furthermore, there was a significantly higher expression in placentas from liveborn children than in placentas from stillborn/aborted fetuses and also a higher expression in second- than in third-trimester placentas. These data suggest that TLR2 expression in the trophoblast could be involved in the response to infectious pathogens in the placenta.