Experimental study on the fine structure of chicken liver parenchyme with special references to extrasinusoidal macrophages and sinusoidal blood cells. Part 1. Sinusoidal cells and macrophages in the normal and India ink-perfused livers.

The chicken livers were electron microscopically observed under a normal condition and after an intravenous India ink perfusion. Kupffer cells and sinusoidal endothelial cells commenced to endocytose India ink particles in the earliest stages (15 min) after perfusion. The attachment of the particles to the cell surface occurred only in the Kupffer cells, which actively took up the particles with coated caveolae. In the endothelial cells the particles were ingested by pinocytosis in the perikaryon and deposited in the macropinocytic vacuoles of Wisse. In Kupffer and endothelial cells, the particles were stored most abundantly at 30 min and 4 hr after perfusion, respectively. At 48 hr, the vacuoles containing the particles were decreased in number and size, while mitotic figures were revealed in the Kupffer cells. Ito cells occasionally ingested in later stages (4 and 48 hr) a few carbon particles; they underwent no mitotic division. Extrasinusoidal macrophages scattered in the parenchyme and phagocytic reticular cells (macrophages) in the lymphoid tissues exhibited phagocytic activity only in later stages (1-4 hr). In 48 hr after the perfusion both cells began to store amounts of the particles in their vacuoles. This delayed phagocytic activity may be ascribed to the location of the cells separated from the sinusoid by the endothelium. Some solitary macrophages projecting a long process into the sinusoid took up the particles at earlier stages. At 48 hr, several mitotic divisions took place in the phagocytic reticular cells of the lymphoid tissue, while no mitotic divisions were found in the solitary macrophages in the parenchyme. After the ink perfusion, migration of solitary macrophages into the sinusoid was accelerated and images indicating their transformation into Kupffer cells were frequently detected. It was concluded that the Kupffer cells maintain their necessary number not only by their self-proliferation but also by replenishment from the extrasinusoidal solitary macrophages scattered in the hepatic parenchyme, which in turn are replenished from the phagocytic reticular cells in the lymphoid tissue capable of mitotic proliferation.