Membrane-bound glycoconjugates of fetal mouse erythropoietic cells with special reference to phagocytosis by hepatic macrophages
Two forms of mononuclear cells were seen in the liver sinusoids of an 11-day mouse embryo. They were qualitatively and cytometrically examined by light and electron microscopy. The first form consisted of free macrophages which possessed erythrophagosomes in the cytoplasm, many cytoplasmic extensions on their cell surface and clear vesicles singly or in groups in the cell periphery. The average cell diameter of macrophages was 10.4 +/- 1.6 microns and the nuclear-cytoplasmic (N-C) ratio 0.36 +/- 0.11. The second form of mononuclear cells in the sinusoids was free from large heterophagosomes. The majority of them ranged from 7 to 12 microns in cell diameter and had a larger N-C ratio than the first form. The cytometrical results showed that the two types of mononuclear cells contained in the sinusoids of the 11-day embryo are similar in properties to the mononuclear cells in extraembryonic and yolk sac vitelline vessels before the start of liver hemopoiesis. The origins of sinusoidal mononuclear cells of these two forms are discussed in relation to the yolk sac ones.