A morphological and immunohistochemical study on the relationship between central macrophage of erythroblastic islands and sinusoidal macrophages in the mouse fetal and neonatal liver *
To clarify the relationship between fetal macrophages in hematopoietic liver and resident macrophages, Kupffer cells, in the sinusoids of postnatal livers, an immunohistochemical study with rat anti-mouse macrophage monoclonal antibody F4/80 and histochemical staining for iron as well as electron microscopic observations were carried out. There was a rapid increase in the number of F4/80-positive cells per unit area (1 mm2) fromll days of gestation, but then there was a significant decrease between 4 and 13 days after birth (p<0.0l). At ll days of gestation, liver anlages contained a few F4/80-positive cells in primitive sinusoidal lumina. The macrophages showed active phagocytosis as scavengers, and contained Fe-positive phagosomes. In the livers at 13 days of gestation, F4/80-positive cells were identified among hepatic cell cords as central macrophages of erythroblastic islands in the hematopoietic foci. The central macrophages contained phagosomes derived from extruded nuclei of definitive erythroblasts and Fe-positive inclusions. At 19 days of gestation, F4/80-positive cells were observed in hematopoietic foci, and a few F4/80-positive cells without hematopoietic cells also appeared among hepatocytes. Although the majority of F4/80-positive cells among hepatocytes contained Fe-positive inclusions, a few small F4/80-positive but Fe-negative mononuclear cells also appeared. A few large macrophages underwent cell death not only through classical apoptosis but also through a process called "dark cell formation." At 13 days of age, F4/80-positive reactions were identified only in sinusoidal macrophages, and F4/80-positive cells were Fe-negative. Some of primitive macrophages derived from the yolk sac underwent cell death and disappeared from the liver shortly after birth. The small F4/80~positive but Fe-negative mononuclear cells in early postnatal livers could be considered as a candidate for a precursor of hepatic resident macrophages of Kupffer cells. (Accepted on September 19, 2003)
