Summary CD4+ CD25 bright regulatory T (Treg) 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 Treg 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 Treg cells was present in pre-eclampsia, and these changes might break the maternal tolerance to the fetus.

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The increased levels of T CD4(+)45RO(+) and T CD8(+) CD25(+) cells can suggest the activation of CD4(+) and CD8(+) T lymphocytes in pre-eclampsia. It seems possible that the activation of T lymphocytes is associated with the deficiency of T regulatory cells in PE.

These results suggest that in patients with preeclampsia there is Th1/Th2 imbalance, with predominant Th1 immunity.