Trophoblast stem cells and syncytiotrophoblasts lack inflammatory responses to LPS but retain robust interferon-mediated antiviral immunity.

ABSTRACT: Early pregnancy requires a tightly regulated pro-inflammatory environment shared between the primitive placenta and decidua. While immune balance supports successful implantation and placental invasion, disruptions in immune signaling during this period can impair implantation and lead to embryo loss. In this study, we investigated the molecular mechanisms underlying immune imbalance during implantation using a trophoblast stem cell (TSC) model. TSCs were cultured in either stem cell or syncytiotrophoblast (STB) differentiation medium and treated with either lipopolysaccharides (LPSs) or interferon beta (IFNB). RT-qPCR and western blotting revealed that LPS failed to induce a pro-inflammatory cytokine response in TSCs or STBs. In contrast, IFNB triggered a strong antiviral response in both TSCs and STBs. RNA sequencing of IFNB-treated TSC and STB 3D spheroids revealed subtle differences between the TSC and STB responses to interferons. Both TSC and STB IFNB-treated spheroids mount an interferon-mediated antiviral response; however, STB spheroid genes associated with the type I interferon response, viral RNA/DNA sensing, and antigen processing were upregulated. We also compared the interferon response between the CT27 (female) and CT29 (male) TSCs and STBs. While STBs showed minimal differences, the CT29 TSCs exhibited a markedly stronger interferon response than the CT27 TSCs. Collectively, these findings suggest that the primitive placenta is selectively responsive to interferon signaling rather than direct pathogen-associated stimuli. This implies that maternal immune activation, rather than microbial invasion, likely drives that placental immune response and embryo success at this stage. Understanding these dynamics underscores the importance of the maternal immune balance in early pregnancy success.

LAY SUMMARY: The maternal immune system has a direct influence on the success of embryo implantation. If that balance is disturbed, the placenta can fail to invade into the uterus and implantation can fail, leading to embryo mortality and pregnancy loss. In our study, we used stem cells from the placenta to explore how they respond to different kinds of immune signals (i.e. signals from bacteria versus signals from the mother's immune response). We found that placental stem cells do not respond to signals from bacteria. However, they do react strongly to signals that resemble a viral infection in the mother. These data suggest that the early placenta is more sensitive to the mother's immune signals than to direct infection, which highlights the critical role of maternal immune health in early pregnancy.