The unique pathophysiology of early-onset severe preeclampsia: role of decidual T regulatory cells

Immunological mechanisms play a pivotal role in the pathophysiology of preeclampsia. T regulatory cells (Treg cells, FoxP3+) suppress the cytotoxic T cell (CD8+) and natural killer (NK) cell response, thereby promoting immunological tolerance to the fetus. In peripheral blood, Treg cells are elevated during pregnancy, decrease throughout gestation, and are decreased in preeclampsia. To determine their role at the implantation site, we characterized the proportion of decidual Treg and CD8+ cells, and compared these with placental histology, villous sFlt expression, and chorionic trophoblast apoptotic index in normal and preeclamptic pregnancies. Decidua from first (n = 5) and second (n = 4) trimester terminations and chorioamniotic membranes, containing decidua, from term deliveries (n = 14), early-onset (≤34 weeks) (n = 12), and late-onset (>34 weeks) (n = 14) severe preeclampsia were evaluated. Immunohistochemistry for CD3, CD8, and FoxP3 was performed: CD8+ and FoxP3+ cells were calculated as a proportion of CD3+ cells. Placental tissue was evaluated for villous hypermaturity and sFlt staining. Chorioamniotic membranes were evaluated, via TUNEL assay, for chorionic trophoblast apoptosis. Decidual Treg cells were seen to peak in second trimester and decrease with advancing gestational age and were lower in early-onset (0.46%) compared with late-onset severe preeclampsia (3.34%) and term pregnancies (5.21%). The proportion of CD8+ cells was higher in cases of severe preeclampsia. Early-onset severe preeclamptic cases had the highest sFlt score, placental insufficiency score, and apoptotic index. Our data suggest that early-onset severe preeclampsia has a unique pathophysiology involving defective immunoregulatory pathways, potentially causing vascular and trophoblast damage at the implantation site.