**3. Summary and Conclusions**

Compared to other pregnancy complications, PE is the main cause of maternal morbidity and mortality. For several decades, researchers have been trying to understand the causes of PE, considering the disorder from different points of view. An important aspect of PE development is the response of maternal innate immunity to various proinflammatory stimuli from the placenta. Normally, the maternal organism adapts to the presence of the fetus; however, at PE, a pronounced inflammatory process occurs. The consequences of this process are manifested in the increased monocyte numbers and altered subset composition, including changes in counts and polarization of placental macrophages. The recent examples of observations listed in this review sugges<sup>t</sup> that monitoring of blood composition and phenotyping of monocytes over the course of pregnancy might be considered as screening tests for PE. However, such tests must be used in combination with other PE prognostic markers because the symptoms of some other complications and conditions (e.g., stress, infections or cancer) occasionally could mimic the PE-associated monocyte changes [8]. Monocytes and tissue macrophages are the extremely important cell types involved in PE pathogenesis. Their possible application as PE predictors and/or therapeutics agents holds grea<sup>t</sup> promise.

**Author Contributions:** Writing—original draft preparation, P.V., A.E., T.F.; writing—review and editing, T.F., G.S.; supervision, T.F., G.S.; project administration, G.S.

**Funding:** This research was funded by President Grant for Government Support of Young Russian Scientists No. 075-15-2019-1120, P.V. was supported by the President's Scholarship (SP-4132.2018.4).

**Acknowledgments:** We are very grateful to Priluchnyi Vlad for the help in illustration of the article.

**Conflicts of Interest:** The authors declare no conflict of interest.
