Chemokine ligand and receptor expression in the pregnant uterus: reciprocal patterns in complementary cell subsets suggest functional roles.

During human pregnancy, the uterus is infiltrated by a population of maternal leukocytes that co-exist with fetal cytotrophoblasts occupying the decidua and uterine blood vessels. These immune cells, termed "decidual granulated leukocytes," are composed predominantly (70%) of the CD56(bright) subset of natural killer cells, accompanied by T cells (15%) and macrophages (15%). The mechanisms underlying the recruitment of these cells are unknown, but by analogy to other systems, chemokines are likely to be involved. We examined the expression patterns of 14 chemokines in the decidualized uterine wall by in situ hybridization, and the expression of chemokine receptors on decidual leukocytes by RNase protection. The striking concordance between the expression of chemokines in the uterus and their receptors on decidual leukocytes allowed us to identify numerous receptor-ligand pairs that may recruit the latter cells to the uterus during pregnancy. Additionally, chemokine expression patterns suggested other, nonimmune functions for these molecules, including a role in cytotrophoblast differentiation. Together, our results imply that chemokine networks serve important functions at the maternal-fetal interface.