IL-18 produced by pregnant uterus promotes essential inflammatory responses and fetoplacental growth.

Placental insufficiency affects fetomaternal health throughout life. Although the interaction between the maternal uterine immune milieu and fetus-derived cells plays a crucial role in placental formation, several aspects remain unclear. Therefore, we conducted this study to investigate the effects of interleukin (IL)-18, a distinctive cytokine with both proinflammatory and anti-inflammatory properties, on the uterine immune milieu and placental development. Our results identified pregnant uterine smooth muscle cells as an important source of IL-18, which supports homeostatic type 1 immune responses. IL-18 facilitates appropriate placental development through uterine vascular remodeling and placental angiogenesis. Smooth muscle cell-specific Il18 knockout dam mice exhibited excessive cytotoxicity of uterine natural killer (NK) cells, impaired fetoplacental growth, and elevated maternal blood pressure, reflecting preeclampsia-like phenotypes. Their offspring demonstrated a tendency toward excessive weight gain and delayed neurodevelopment. Overall, this study emphasizes the essential role of IL-18 in placental formation and its wider implications for fetomaternal health.