Monocytes and macrophages in pregnancy: The good, the bad, and the ugly*

Abstract

A successful human pregnancy requires precisely timed adaptations by the maternal immune system to support fetal growth while simultaneously protecting mother and fetus against microbial challenges. The first trimester of pregnancy is characterized by a robust increase in innate immune activity that promotes successful implantation of the blastocyst and placental development. Moreover, early pregnancy is also a state of increased vulnerability to vertically transmitted pathogens notably, human immunodeficiency virus (HIV), Zika virus (ZIKV), SARS‐CoV‐2, and Listeria monocytogenes. As gestation progresses, the second trimester is marked by the establishment of an immunosuppressive environment that promotes fetal tolerance and growth while preventing preterm birth, spontaneous abortion, and other gestational complications. Finally, the period leading up to labor and parturition is characterized by the reinstatement of an inflammatory milieu triggering childbirth. These dynamic waves of carefully orchestrated changes have been dubbed the “immune clock of pregnancy.” Monocytes in maternal circulation and tissue‐resident macrophages at the maternal‐fetal interface play a critical role in this delicate balance. This review will summarize the current data describing the longitudinal changes in the phenotype and function of monocyte and macrophage populations in healthy and complicated pregnancies.

Isolation of Decidual Macrophages and Hofbauer Cells from Term Placenta—Comparison of the Expression of CD163 and CD80

“…Their number is variant depending on the week of pregnancy and is reduced in term placenta compared to first trimester placenta. Hofbauer cells are located in the chorionic villi nearby the villous vessels, their contribution varies between term and first trimester placenta [ 36 , 61 ]. Thomas et al was able to differentiate distinct macrophage populations in first trimester placenta by using CD45 and CD14 as main markers to identify placental macrophages.…”

Introduction to the immunology of pregnancy

“…This function depends upon the innate immune system's capacity to coordinate cell migration for surveillance, and to recognize and respond to invading microorganisms. During normal pregnancy, the human decidua contains a high number of immune cells, the majority innate immune cells, such as macrophages, dendritic cells (DCs), natural killer (NK) cells, and adaptive immune cells such as CD4 + T cells, CD8 + T cells and regulatory T cells (Treg) 13 . These cells are not indifferent from the presence of the fetus and interact with the cellular component of the placenta, the trophoblast.…”

“…Sun et al immune cells such as CD4 + T cells, CD8 + T cells and regulatory T cells (Treg). 13 These cells are not indifferent from the presence of the fetus and interact with the cellular component of the placenta, the trophoblast. Additionally, their presence was used as evidence of immune sequestration; however, work from us and many others has proved that immune cells at the decidua are a fundamental component for the success of the pregnancy.…”

“…Additionally, their presence was used as evidence of immune sequestration; however, work from us and many others has proved that immune cells at the decidua are a fundamental component for the success of the pregnancy. [13][14][15][16][17][18][19][20] These cells play a unique role maintaining the balance between tolerance to paternal antigens, support of the developmental process of fetal growth and the protection against pathogens that could endanger the success of pregnancy. The role of NK cells, macrophages, and T cells is extensively reviewed in this issue.…”

“…The role of NK cells, macrophages, and T cells is extensively reviewed in this issue. 7,8,13,21 From an immunological point of view, pregnancy was considered a monolithic process where the function of immune cells and the immunological environment are the same in the first, second and third trimester. However, we observed that dendritic cells are essential for the preparation of the endometrium for implantation by creating an inflammatory environment 22,23 leading us to change the concept that pregnancy is only an anti-inflammatory environment.…”