Nguyen N, et al. – Here, researchers look to comprehend the local immune microenvironment of the uteroplacental interface (UPI) to identify the critical factors mediating maintenance of maternal – fetal tolerance. The dramatic differences in cell type proportions, phenotypes and functionality they found between lymphocytes at the UPI vs peripheral blood (PB) indicate a specific local immune microenvironment that develops at the UPI. The signals – and mechanisms that attract and retain lymphocytes at the UPI are unknown but likely important for the understanding of how the necessary tolerogenic environment for a successful pregnancy is established and maintained.