Placental macrophages: Origin, heterogeneity, function and role in pregnancy-associated infections

Abstract

Placental macrophages are a heterogenous population of immune cells present throughout pregnancy. They are essential for maintenance of the homeostatic placenta environment and host defense against infections. The characterization of placental macrophages as well as their activation have been limited for a long time by the lack of convenient tools. The emergence of unbiased methods makes it possible to reappraise the study of placental macrophages. In this review, we discuss the diversity and the functions of placental macrophages to better understand their dysfunctions during placental infections.

Molecular Pathology Analysis of SARS-CoV-2 in Syncytiotrophoblast and Hofbauer Cells in Placenta from a Pregnant Woman and Fetus with COVID-19

“…Generally believed to be of fetal origin, Hofbauer cells are more abundant during the 1st and early 2nd trimester of pregnancy than in later gestation. The physical location of Hofbauer cells in close proximity to chorionic villus vessels, as well as the trophoblast layer, is significant in cases of potential transfer of substances and microbial agents across the maternal-placental interface [ 20 , 24 , 25 , 26 ].…”

“…Hofbauer cells are implicated in a number of infectious diseases that affect pregnant women, and have been identified as targets for some viruses, protozoans, and other pathogens [ 20 , 28 , 29 ]. Hofbauer cells have also been found to be increased in number, and in some cases proliferate, in cases of intrauterine placental infection caused by a variety of TORCH agents, as well in placentas having villitis, an inflammatory abnormality of the chorionic villi having a number of different etiologies [ 24 , 25 , 28 , 29 , 30 , 31 , 32 , 33 ].…”

“…Hofbauer cells are a morphologically and antigenically heterogeneous group of macrophages that reside in the stroma of the chorionic villi throughout pregnancy. These villous macrophages have been implicated in the pathogenesis of several pathogens (termed TORCH agents) capable of intrauterine transplacental transmission, including Zika virus, human immunodeficiency virus (HIV), Trypanosoma cruzi , and others [ 20 ]. In order to better understand the potential mechanisms of SARS-CoV-2 transplacental transmission, we utilized molecular pathology techniques to evaluate viral distribution within chorionic villi of a placenta having extensive syncytiotrophoblast infection from a maternal-fetal dyad testing positive for the virus, with particular attention to Hofbauer cell involvement, and discuss the findings in terms of mechanisms of intrauterine transmission.…”

From Coxiella burnetii Infection to Pregnancy Complications: Key Role of the Immune Response of Placental Cells

“…The anatomopathological examination of animal placentas reveals significant damage to the tissue (Table 1). Inflammatory response and some injury as a consequence are identified in C. burnetii-positive placenta from goats, ewes and cows [42,45,47]. Necrosis yellow/brownish exudates are found in C. burnetii-positive placentas from abortions and non-abortive pregnancies [5].…”

“…The examination of infected placentas from goats, cows, or mice using immunochemistry reveals the presence of C. burnetii organisms in this tissue (Table 1). A direct detection of C. burnetii using the polymerase chain reaction technique has confirmed the presence of bacteria in the placental tissue of goats, cows, ewes, calves, and mice [1,21,22,[42][43][44]]. The bacterium is found at the extracellular level, mainly in necrotic areas, or in placental cells through immunohistochemistry [43,44].…”