Abstract
The present investigation has been made to elucidate a possible origin of the human placental macrophages. On the 6th week of gestation, ultrastructurally identifiable blood cells in the vascular lumen are almost exclusively primitive erythroblasts, among which there are only a small number of mononuclear cells with poorly developed organelles, large nucleo-cytoplasmic ratio and several microvilli on the cell surface. On immunoelectron microscopy, these cells are positive for FMC 32 monoclonal antibody. In the same stage, numerous macrophages have already appeared in the stroma, most of which stain prominently with the monoclonal antibody. With the lapse of gestation, they gradually become to show positive reactions for HLe-1, PHM 2, PHM 3 and anti-S-100 protein α chain monoclonal antibodies.
Electron microscopically, immature mononuclear cells are observed in the vascular lumen of chorionic plate of mouse placenta on 10 days of gestation, while similar cells are confirmed in the yolk sac on 9 days of gestation. On 11 days of gestation, mature macrophages are found in the stroma of chorionic plate. Immunoelectron microscopy has revealed that faintly positive reaction products for F4/80 monoclonal antibody are localized on the cell surface of immature mononuclear cells, whereas the mature macrophages are intensely positive for F4/80 monoclonal antibody. Furthermore, CFU-C assay with LP3-conditioned medium discloses the occurrence of macrophage precursors in the placenta a day after the development of immature macrophages in the yolk sac. These results suggest that the macrophages, including Hofbauer cells, within the stroma of chorionic villi in the early stage of gestation are derived from macrophages or their precursor cells originating in the yolk sac hematopoiesis.
