The role of decidual immune cells on human pregnancy

The maternal-fetal interface undergoes dynamic changes to allow the fetus to grow and develop in the uterus, despite being recognized by the maternal immune cells. Within the innate immune system, decidual natural killer cells and antigen presenting cells (including macrophages and dendritic cells) that comprise a large proportion of the decidual leukocyte populations play an important role in modulating trophoblast invasion, angiogenesis and vascular remodeling. On the other hand, within the adaptive immune system, CD8(+) T cells, effector CD4(+) T cells, Foxp3(+) regulatory T cells and CD4(+)HLA-G(+) suppressor T cells are identified as potential players in maintaining immune tolerance toward the semi-allogeneic fetus. This review discusses how these key immune cells contribute to pregnancy outcome and the complex interactions between the innate and adaptive immune system during human pregnancy.