CD4+CD25high regulatory T cells in human pregnancy

Although both human and mouse CD4+CD25+ Treg have potent regulatory properties, surface phenotypes of human CD4+CD25+ Treg cells are not exactly the same as those of mouse CD4+CD25+ Treg cells. Murine CD4+CD25+ T cells are homogenous and exhibit regulatory function. On the other hand, CD4+CD25high T cells are the only cells which exhibit regulatory function in humans. Humans CD4+CD25low cells have no ability for immunosuppression. CD4+CD25high T cells inhibit the immunostimulation of conventional T cells through cell-to-cell contact or immunosuppressive cytokines such as interleukin 10 and transforming growth factor-β. As another mechanism of immunosuppression, CTLA-4 on CD4+CD25+ regulatory T cells up-regulate indoleamine 2,3-dioxygenase (IDO) expression in dendritic cells which play important roles for immunosuppression. Here, we review the differences between humans and mouse Treg cells and the role of CD4+CD25+Treg during pregnancy.