An atlas of around 70,000 cells from first trimester placentas provides novel insights into cellular organization and communication during the early stages of human pregnancy, reports a paper published in this week’s Nature. These findings explore the mechanisms that maintain the physiologically stable environment vital to successful pregnancy.

During early human pregnancy, the fetal placenta implants into the uterine lining (decidua), where placental trophoblast cells mingle with maternal cells. This relationship is critical to successful pregnancy, yet the cell-cell interactions in the decidua during early pregnancy are poorly understood. International research initiatives such as the Human Cell Atlas are working to identify cell types involved in development, health, and disease.

As part of this effort, Sarah Teichmann and colleagues profiled the transcriptomes (the set of RNA molecules that control the expression of genes) of around 70,000 cells from human first-trimester (6-14 weeks) placentas with matched maternal blood and decidual cells. They studied the molecular interactions between fetal and maternal cells at the placental-decidual interface, and used these data to develop a novel statistical tool (CellPhone) to predict possible specific cell-cell interactions. The authors uncover specialized functions of individual subsets of cells, and identify regulatory interactions that could help minimize damaging maternal immune responses. Additionally, the authors identify three main subsets of decidual natural killer (dNK) cells. They suggest that contact between cells from one of these subsets, dNK1, and particular placenta cells during a first pregnancy may prime dNK1 cells to respond more effectively to placental implantation in subsequent pregnancies.

These findings provide an essential resource for understanding early pregnancies, and could have implications for improving the diagnosis and treatments of pregnancy-related disorders.