Proportion of peripheral blood and decidual CD4⁺ CD25 ^bright regulatory T cells in pre-eclampsia

CD4⁺ CD25^bright regulatory T (T_reg) cells have been identified as a principle regulator of tolerance during pregnancy. In the setting of pre-eclampsia, however, little is known about the dynamics of these cells. In the current study, we determined CD4⁺ CD25 ^bright T_reg cells in the peripheral blood using flow cytometry and forkhead box P3 (FoxP3⁺) cells at the placental bed using immunohistochemical staining. Peripheral blood mononuclear cells (PBMC) of 38 pre-eclamptic cases (17 cases Japanese, 21 cases Polish), 40 normal late pregnancy subjects (20 subjects Japanese, 20 subjects Polish), and 21 non-pregnant healthy controls (10 subjects Japanese, 11 subjects Polish) were included. We found the percentage of CD25^bright cells within the CD4⁺ T cell population in PBMC was reduced significantly in both Japanese and Polish pre-eclamptic cases than in normal pregnancy subjects (P < 0.001) and non-pregnant healthy controls (P < 0.001). Also, the percentage of FoxP3⁺ cells within CD3⁺ T cells in the placental bed biopsy samples of pre-eclamptic cases were decreased compared to those in normal pregnancy subjects. These findings suggest that a decreased number of T_reg cells was present in pre-eclampsia, and these changes might break the maternal tolerance to the fetus.