In a healthy pregnancy, a finely tuned maternal immune response prevents the mother's body from rejecting the growing fetus. But in some pregnancies, this response goes haywire, leading to a potentially dangerous complication known as chronic placental inflammation. To understand what drives this inflammation, researchers led by Nardhy Gomez-Lopez, Ph.D., a professor of obstetrics and gynecology and of pathology and immunology at WashU Medicine, used spatial and single-cell gene and protein expression profiling to map the immune cell landscape of the placenta in mothers who developed chronic placental inflammation, down to individual cells at the junction connecting the mother and fetus.