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HLA-DR is absent in primitive macrophages through epigenetic silencing of master regulator CIITA

ABSTRACT: The earliest macrophages are generated during embryonic development from erythro-myeloid progenitors (EMPs) via primitive haematopoiesis. This process is poorly understood in humans and in the mouse is thought to be spatially restricted to the yolk sac. Human fetal placental macrophages, Hofbauer cells (HBC), arise during the primitive haematopoietic wave at ~18 days post conception. Here we identify a population of placental erythro-myeloid progenitors (PEMPs) in the early human placenta that give rise to HBC. PEMP are fetal CD34+CD43+ progenitors found exclusively at early gestational timepoints. Transcriptomic analyses reveal that PEMP have conserved features of primitive yolk sac EMPs, including the lack of HLF expression. Using in vitro single-cell culture experiments we show that PEMP generate HBC-like cells that completely lack HLA-DR expressionÃ‚Â and demonstrate that this is a conserved feature of all macrophages generated by primitive haematopoiesis in humans. Finally, we demonstrate that the class II transactivator, CTIIA, the master regulator HLA-DR expression, is epigenetically silenced during primitive haematopoiesis, leading to HLA-DRneg macrophages. These findings demonstrate that HBC are derived locally from PEMP and establish the human placenta as an additional site of primitive haematopoiesis.

PROVIDER: EGAS00001006981 | EGA |

REPOSITORIES: EGA

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Project description:A major population of placenta macrophages represented throughout the pregnancy consists of CD14+ macrophages, but their characteristics remain badly understood. Here we purified from placentas at term CD14+ macrophages using positive selection. The phenotyping of CD14+ macrophages performed using flow cytometry revealed that placenta CD14+ macrophages expressed a series of markers distinct of those of circulating monocytes monocyte-derived macrophages. Placenta CD14+ macrophages spontaneously matured in multinucleated giant cells (MGCs) as demonstrated by size, number of nuclei display and specific cytoskeleton organization. Placenta CD14+ macrophages and MGCs were phagocytic cells but the potential of MGCs to mount an inflammatory response was lower than that of their precursors. Placenta CD14+ macrophages and MGCs stimulated with interferon and interleukin-4 were not polarized into typical M1 or M2 profiles. Placenta macrophages exhibited specific activation transcriptional programs. Indeed, principal component analysis and hierarchical clustering show that placental macrophages formed a distinct group from circulating monocytes and monocyte-derived macrophages. Among placenta macrophages, it was also possible to distinguish CD14+ macrophages and MGCs. In addition, networks based on gene interactions were clearly different in CD14+ macrophages and MGCs. Finally, the microenvironment of placenta CD14+ macrophages governs their differentiation into MGCs because CD14+ macrophages incubated with trophoblasts exhibited exarcerbated characteristics of MGCs and because the co-incubation of circulating monocytes from working women with trophoblast supernatants resulted into the formation of MGCs whereas monocytes from non-pregnant women incubated with trophoblast supernatants did not differentiate into MGCs. Taken together, these results clearly demonstrated specific feaures of placenta CD14+ macrophages. Three replicates of each of the following: 1. Placental macrophages just after isolation (CD14+ macrophages) 2. Placental macrophages after 9 days in culture (MGCs) 3. CD14+ cells isolated from PBMC which are extracted from the whole human blood of healthy donors (Monocytes) 4. Macrophages derived from monocytes (MDMs)

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HLA-DR is absent in primitive macrophages through epigenetic silencing of master regulator CIITA

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