Scoping Review of Maternal Monocytes and the Syncytiotrophoblast: Bi-Directional Communication in the Intervillous Space

The relationship between maternal monocytes and the placenta is crucial for successful pregnancy. As existing reviews focus on the research on decidual macrophages or Hofbauer cells (fetal macrophages), we conducted a scoping review of literature studies examining the relationship between circulating maternal monocytes and the villous trophoblast. The goal of this review was to outline existing research within the field, disseminate further information, and to identify current knowledge gaps within the field. We searched the PubMed (MEDLINE) database for relevant articles published since 1995 that studied human tissue or cell lines. Our results showed clear trends in the type of monocyte and placental primary tissues and cell lines used. Further classification of these articles revealed four primary categories of monocyte-trophoblast interaction research: monocyte presence or recruitment to the placenta, monocyte phenotype in the intervillous space, monocyte-placental adhesion, and monocyte interaction with syncytiotrophoblast-derived extracellular vesicles (STBEVs). Although limited in scope and number, these studies implicate the importance of monocyte-trophoblast interactions, and their significant roles in maternal disease.