During pregnancy several maternal a

During pregnancy several maternal and fetal mechanisms are established to prevent a destructive immune response against the allogeneic fetus. Despite these mechanisms, fetus specific T-cells persist throughout gestation but little is known about the regulation of these T-cells. Recently, CD4+CD25+ regulatory T-cells have been identified in human decidua. Human decidua forms the maternal part of the fetal–maternal interface and is subdivided in two distinct regions: the decidua (d.) basalis and the decidua (d.) parietalis. The aim of this study was to determine the distribution of specific T-cell subsets in d. basalis and d. parietalis in early and term pregnancy, with a special emphasis on the presence of CD4+CD25bright (regulatory) T-cells and CD8+CD28− (suppressor) T-cells. In addition, we compared phenotypic characteristics of decidua derived T-cell subsets with maternal peripheral blood (mPBL) T-cells and T-cells from non-pregnant controls. We identified significantly higher percentages of CD4+CD25bright and CD8+CD28− T-cells in decidua compared to peripheral blood suggesting an important role for these T-cell subsets locally at the fetal–maternal interface. The major differences in T-cell subset distribution and the presence of additional phenotypic differences between T-cells in d. basalis, d. parietalis and mPBL may reflect specific immunomodulatory functions of these T-cell subsets at these different sites during pregnancy.