Human pregnancy: the role of chemokine networks at the fetal-maternal interface.
Chemokines are multifunctional molecules initially described as having a role in leukocyte trafficking and later found to participate in developmental processes such as differentiation and directed migration. Similar events occur in pregnancy during development of the fetal-maternal interface, where there is extensive leukocyte trafficking and tissue morphogenesis, and this is accompanied by abundant chemokine expression. The relationship between chemokines, leukocytes and placental development is beginning to be delineated. During pregnancy a specialised population of maternal leukocytes infiltrates the implantation site. These leukocytes are thought to sustain the delicate balance between protecting the developing embryo/fetus and tolerating its hemiallogeneic tissues. A network of chemokine expression by both fetal and maternal components in the pregnant uterus functions in establishing this leukocyte population. Intriguingly, experiments investigating immune cell recruitment revealed the additional possibility that chemokines influence aspects of placental development. Specifically, cytotrophoblasts, the effector cells of the placenta, express chemokine receptors that can bind ligands found at key locations, implicating chemokines as regulators of cytotrophoblast differentiation and migration. Thus, as in other systems, at the fetal-maternal interface chemokines might regulate multiple functions.