CX3CR1 regulates the immune microenvironment in the placenta

The immune environment at the maternal-fetal interface is highly regulated and changes depending on the stage of pregnancy. Any dysregulation or imbalance of the pro- and anti-inflammatory stages can disrupt placental development and can lead to various obstetric disorders, such as miscarriage, preterm birth, and preeclampsia. Several inhibitors interfering with inflammatory pathways have been tested to treat dysregulated inflammation during pregnancy, but they were associated with adverse responses to mother and child. Therefore, understanding factors regulating immune responses at the maternal-fetal interface could lead to the discovery of novel therapeutic targets that prevent detrimental pregnancy outcomes caused by inflammation without risks to mother and child. The fractalkine receptor CX3CR1 is crucially involved in inflammatory processes. Additionally, accumulating evidence has indicated a contribution of CX3CR1 in the pathogenesis of obstetric disorders, including preeclampsia and miscarriage. In this study, we investigated the immune regulatory role of CX3CR1 at the maternal-fetal interface. Our results demonstrate widespread expression of CX3CR1 in placental/decidual immune cells but most prominently on maternal and fetal macrophages and monocytes. Moreover, this study demonstrates a crucial role of CX3CR1 in regulating the immune cell environment and highlights an importance in the formation of maternal sinusoids within the placental labyrinth zone. Combined, our data demonstrate an important immunoregulatory role of CX3CR1 at the maternal-fetal interface. Therefore, the CX3CL1/CX3CR1 axis could be a potential therapeutic target used to prevent detrimental pregnancy outcomes resulting from a dysregulated immune environment.