Normal human pregnancy is associated with an elevation in the immune suppressive CD25+ CD4+ regulatory T-cell subset

CD4(+) CD25(+) T regulatory cells (T-Reg), suppress antigen-specific immune responses and are important for allograft tolerance. During pregnancy the mother tolerates an allograft expressing paternal antigens (the fetus) requiring substantial changes in immune regulation over a programmed period of time. We analysed whether immune-suppressive T-Reg cells were altered during pregnancy and therefore might play a part in this tolerant state. The presence of T-Reg cells was assessed in the blood of 25 non-pregnant, 63 pregnant and seven postnatal healthy women by flow cytometry. We observed an increase in circulating T-Reg cells during early pregnancy, peaking during the second trimester and then a decline postpartum. Isolated CD25(+) CD4(+) cells expressed FoxP3 messenger RNA, a marker of T-Reg cells, and suppressed proliferative responses of autologous CD4(+) CD25 T cells to allogeneic dendritic cells. These data support the concept that normal pregnancy is associated with an elevation in the number of T-Reg cells which may be important in maintaining materno-fetal tolerance.