DC-sign+ CD163+ macrophages expressing hyaluronan receptor LYVE-1 are located within chorion villi of the placenta.

The purpose of this study was to investigate with immunohistochemical methods antigen presenting cells and their relationship to blood and lymphatic vessels in human term placenta. Fetal placental antigen presenting cells, historically also known as Hofbauer cells, were located in the chorionic villi below the syncytiotrophoblast and in the vicinity of fetal capillaries. DC-SIGN/CD209 expression was observed on CD163+, CD68+, CD45+, HLA-A,B,C+, DC-LAMP/CD208-, CD86-, Langerin/CD207-, FXIIIa-, CD1a- cells consistent with the macrophage nature of these cells. These fetal DC-SIGN+ cells lack HLA-DR, -DP, -DQ expression. Moreover, we show for the first time that they co-express the hyaluronan receptor LYVE-1. In contrast, no LYVE-1+ vessel structures, i.e. lymphatic vessels, were detected. Human term decidua hosted a variety of CD45+ cells, further phenotyped as CD163+, DC-SIGN+, CD68+, HLA-DR+, HLA-A,B,C+. Mature dendritic cells were never observed in human term placenta. In summary, human term placenta is an immunoprivileged organ without lymphatic drainage and with numerous DC-SIGN+ macrophages within the chorionic villi. We hypothesize that these cells may fulfil a function in innate responses against pathogens as well as be involved in the homeostasis of hyaluronan metabolism in the rapidly differentiating placenta.