Placental immunity is critical for fetal health during pregnancy, as invading pathogens spread from the parental blood to the fetus through this organ. However, inflammatory responses in the placenta can adversely affect both the fetus and the pregnant person, and the balance between protective placental immune response and detrimental inflammation is poorly understood.

Placental immunity is critical for fetal health during pregnancy, as invading pathogens can be transmitted from the maternal blood to the fetus through this organ. However, inflammatory responses in the placenta can adversely affect both the fetus and the pregnant mother, and the balance between protective placental immune response and detrimental inflammation is poorly understood. Extracellular vesicles (EVs) are membrane-enclosed vesicles that play a critical role in placental immunity. EVs produced by placental trophoblasts mediate immune tolerance to the fetus and to the placenta itself, but these EVs can also activate detrimental inflammatory responses. The regulation of these effects is not well-characterized, and the role of trophoblast EVs (tEVs) in the response to infection has yet to be defined. The Gram-positive bacterial pathogen Listeria monocytogenes (Lm) infects the placenta, serving as a model to study tEV function in this context. We investigated the effect of Lm infection on the production and function of tEVs, using a trophoblast stem cell (TSCs) model. We found that tEVs from infected TSCs were immunostimulatory, activating macrophages to a pro-inflammatory state. Surprisingly, this activation made RAW 264.7 macrophages more susceptible to subsequent Lm infection. Increased susceptibility to infection has not previously been reported as an effect of EVs. Proteomic analysis and RNA sequencing revealed that tEVs from infected TSCs had altered cargo compared to those from uninfected TSCs. Together, these results suggest an immunomodulatory role for tEVs during prenatal infection.