Identification of endometrial CD169+ macrophages essential for Treg cell accumulation and implantation.

Successful pregnancy requires coordinated regulation between the innate and adaptive immune systems. Regulatory T (Treg) cells are essential for establishing maternal immune tolerance to the semi-allogeneic fetus, but the innate immune cells that modulate this process remain poorly defined. Here, we identify CD169+ macrophages in the endometrium as critical regulators of Treg cell recruitment and implantation. These CD169+ macrophages are endometrial localized, exhibit an anti-inflammatory phenotype, and secrete chemokines that attract Treg cells to the endometrium. We also identified CD169+ macrophages in the human endometrium that express chemokines involved in Treg cell recruitment. Our findings identify endometrial CD169+ macrophages as key orchestrators of Treg cell accumulation at the maternal-fetal interface, providing mechanistic insight into implantation and conceptus development.