MHC mediated immunoregulation at the fetal–maternal interface

Abstract

During pregnancy maternal lymphocytes at the fetal–maternal interface play a key role in the immune acceptance of the allogeneic fetus. Decidual NK cells contain immune modulatory properties and facilitate trophoblast invasion into maternal tissue. More recently, CD4+CD25bright regulatory T cells have shown to be concentrated in decidual tissue where they are able to suppress fetus-specific and non-specific responses. Immunogenetical analyses showed that a fetal-maternal HLA-C mismatch is crucial for both activation of CD4+ T cells and induction of functional CD4+CD25 bright regulatory T cells. However, decidual CD8+ T cells form the largest fraction of T cells at the fetal-maternal interface. Phenotypic analysis of the decidual and peripheral CD8+ T cell pool showed that decidual CD8+ T cells mainly consist of differentiated Effector-Memory cells while unprimed naive cells are almost absent. Unlike peripheral blood Effector-Memory CD8+ T cells, the decidual Effector-Memory CD8+ T cells do not express perforin and have a reduced expression of granzyme B. Apparently, the functional features of decidual CD8+ T cells do not correspond their matching phenotype in peripheral blood. These data show that decidual CD8+ T cells may pursue alternative means of effector cell differentiation and indicate that not only CD4+ regulatory cells but also decidual CD8+ T cell differentiation and regulation may play a crucial role in maternal immune tolerance to the fetus.