Natural killer 1.1⁺ αβ T cells in the periimplantation uterus

When the developing embryo implants into the uterine wall, resident maternal immune cells may encounter antigens present on the fetal tissues. The nature and constituents of the ensuing maternal immune response, and its regulation, are of considerable interest in understanding normal and abnormal pregnancy. Here, we report the presence of natural killer (NK)1.1⁺ αβ T cells in the murine periimplantation uterus. These cells account for a large portion of both the T-cell and natural killer cell populations in early pregnancy, while their numbers in the non-pregnant uterus and later in pregnancy are greatly reduced. Phenotypically, these NK1.1⁺ αβ T cells belong to a previously described subset of cells that bear a Vα14-Jα281-encoded T-cell receptor. Unlike other organs, where both CD4⁺ and CD4^-/CD8^- NK1.1⁺ αβ T cells are found, the placental/decidual population appears to be entirely CD4^-/CD8^-. The Vβ repertoire of the placental/decidual population is also altered from that of other organs, with a majority of cells expressing Vβ3. Together, these features suggest the possibility of local development. NK1.1⁺ αβ T cells are known to recognize the class I-like CD1 molecule. Consistent with this association, we demonstrate CD1 expression by tissues within the pregnant uterus. Our findings define an additional organ-specific immune environment where NK1.1⁺ αβ T cells may play a role, and continue to demonstrate the specialized nature of the maternal intrauterine immune system during pregnancy.