Preeclampsia (PE) is a poorly understood pregnancy complication. It has been suggested that changes in the maternal immune system may contribute to PE, but evidence of this remains scarce. Whilst PE is commonly experienced prepartum, it can also occur in the postpartum period (postpartum PE-PPPE), and the mechanisms involved are unknown. Our goal was to determine whether changes occur in the maternal immune system and placenta in pregnancies complicated with PE and PPPE, compared to normal term pregnancies. We prospectively recruited women and collected blood samples to determine the circulating immune profile, by flow cytometry, and assess the circulating levels of inflammatory mediators and angiogenic factors. Placentas were collected for histological analysis. Levels of alarmins in the maternal circulation showed increased uric acid in PE and elevated high-mobility group box 1 in PPPE. Analysis of maternal immune cells revealed distinct profiles in PE vs PPPE. PE had increased percentage of lymphocytes and monocytes whilst PPPE had elevated NK and NK-T cells as well. Elevated numbers of immune cells (CD45+) were detected in placentas from women that developed PPPE, and those were macrophages (CD163+). This work reveals changes within the maternal immune system in both PE and PPPE, and indicate a striking contrast in how this occurs. Importantly, elevated immune cells in the placenta of women with PPPE strongly suggest a prenatal initiation of the pathology. A better understanding of these changes will be beneficial to identify women at high risk of PPPE and to develop novel therapeutic targets.

Summary Sentence

Antepartum and postpartum preeclampsia have distinct immune profiles, and analysis of the placenta suggests a prenatal initiation of the postpartum pathology.