Cytokines and chemokines during human embryo implantation: Roles in implantation and early placentation

The complex processes of embryo implantation and early placentation require a plethora of locally acting molecules, which are themselves tightly regulated. Among these are cytokines (including chemotactic chemokines), which are synthesized by several cell types at the maternal-fetal interface. Those produced by endometrial epithelium may be secreted apically into the uterine lumen, where they affect blastocyst development, migration, and attachment, or basally with effects on the transformation of the underlying stroma. Decidualized stromal cells, which subsequently form a major component of the decidua of pregnancy, also produce cytokines that act to drive the decidualization process and chemokines that are chemoattractants both for leukocytes such as uterine natural killer cells and macrophages, and for trophoblast migration. Activated leukocytes within the developing decidua also contribute regulatory cytokines to the local microenvironment. Disturbances in the production of individual cytokines have been demonstrated in the endometrium of some infertile women and in those with recurrent miscarriage. It is important to establish whether a signature of endometrial cytokines may provide a clinically useful indication of women who will experience difficulty in establishing a viable pregnancy.