Innate immune responses to pathogens at the maternal–fetal interface

During pregnancy, the maternal immune system must navigate a balance between fetal tolerance and a response to acquired microbial infections. Cells at the maternal–fetal interface coordinate this response throughout gestational stages in a dynamic manner, integrating endocrine, developmental, inflammatory and metabolic cues. Although many maternal and fetal cell types activate innate immune signalling pathways in response to infections, excessive inflammation can disrupt tolerance, affect placental function and impair fetal development, leading to congenital disease and other pregnancy complications. In this Review, we discuss the mechanisms of pathogen recognition in the maternal and fetal compartments of the placenta and the consequences of these responses to pregnancy outcomes.