The development of strategies to prevent preterm birth and other complications of human pregnancy has been greatly hindered by our current lack of understanding of underlying pathogenic mechanisms. In particular, little is known about the intrinsic inflammatory characteristics of the decidua, the specialized uterine stromal tissue that surrounds the fetus and placenta. This proposal is based upon recent work from my laboratory on the molecular pathways that control decidual inflammation and leukocyte trafficking in the pregnant mouse uterus. We have found that the differentiation of endometrial stromal cells (ESCs) into decidual stromal cells (DSCs) entails the epigenetic silencing of select inflammatory chemokine genes through their promoter accrual of the H3K27me3 repressive histone mark. This novel developmental program dramatically reduces the potential of the decidua to manifest an inflammatory response and accumulate activated T cells. In unpublished data, we have found that DSC differentiation also entails the silencing of Cxcl12 encoding the multifunctional chemokine CXCL12, and Csf1 encoding the macrophage growth factor CSF-1. Together, these findings raise the question of whether an analogous decidual gene silencing program is active in human DSCs, and suggest that dysregulation of this program may underlie a variety of placental/decidual pathologies. The proposal is divided into three Specific Aims. Aim I seeks to gain greater insight into the breadth, molecular characteristics, and functional significance of decidual gene silencing, again using mice as a model organism. These experiments will establish a foundation for evaluating decidual gene silencing in human pregnancy, and for considering its potential significance with regards to human pregnancy complications. Aim II, which constitutes the bulk of the proposal, employs fresh first trimester decidual specimens and a number of biochemical techniques to determine whether decidual gene silencing is a feature of human pregnancy. Aim III develops a novel histone mark immunostaining/DNA fluorescence in situ hybridization (DNA-FISH) protocol for detecting the decidual gene silencing program at the single cell level so that potential dysregulation of this program can ultimately be detected in archived placental/decidual pathological specimens.