Isolation and characterization of Hofbauer cells from human term placentas

Hofbauer cells (HBCs) are macrophages of fetal origin present in the human placenta that play a key role in maintaining a healthy pregnancy. They are the most abundant immune cells (> 90%) in the placental villi. They have been implicated in various complications of pregnancy, though their role in these pathologies remains rudimentary. In addition, despite being discovered over a century ago, there is no consensus on the specific time window between delivery and placental sample processing for HBCs isolation, the site of biopsy sampling, and isolation protocol. In previous studies, mechanical disintegration, enzymatic digestions, density gradient separation, homogenization, adherence, rosetting, and immune selection techniques have been used to isolate HBCs for immunological studies. Here we review current knowledge on HBCs isolation methods, their role in healthy and pathologic pregnancy, and the impact of pregnancy complications on HBCs population and phenotype. A literature search was conducted on Scopus, PubMed, and Google Scholar databases using specific keywords, including "Isolation of Hofbauer cells, Hofbauer cells and infectious diseases, Hofbauer cells on immune function, and Hofbauer cells and maternal autoimmune pathology." No restrictions were placed on the year of publication or author affiliation during the selection process. Developing a standardized and harmonized HBCs isolation technique(s) will allow comparative studies across laboratories, research groups studying HBCs. These standardized approaches will provide the necessary impetus for studies on HBCs and their functionality in healthy and placental pathologies.