MATURATION OF RAT DENDRITIC CELLS DURING INTRAHEPATIC TRANSLOCATION EVALUATED USING MONOCLONAL-ANTIBODIES AND ELECTRON-MICROSCOPY

Specific populations of hepatic sinusoidal cells were stained with mon oclonal antibodies that recognize monocytes/macrophages (ED1), tissue macrophages (Kupffer cells) (ED2), MHC class II (Ia) antigen (MRC OX6) , and dendritic cells/gamma,delta T-cells (MRC OX62) and analyzed by l ight and electron microscopy. The majority of ED1(+) and/or ED2(+) cel ls were localized to the hepatic parenchyma, whereas OX6(+) and/or OX6 2(+) cells were more densely distributed within Glisson's sheath than in the hepatic parenchyma. Double-immunoperoxidase staining of normal liver for ED1, ED2, and OX6 identified dendritic cells (DC) of two dif ferent phenotypes, ED1(+)ED2(-)OX6(+) and ED1(-)ED2(-)OX6(+). DC can b e classified into three different types based on ultrastructural chara cteristics. The first type (type I) is characterized by one or more lo ng cytoplasmic processes and a well-developed lysosomal system. The se cond type (type II) has an inconspicuous lysosomal system, abundant hy aloplasm, and characteristic short cytoplasmic processes. The third ty pe (type I-II) has cytologic features intermediate between those of ty pe I and type II DC. At the electron-microscopic level, these three ce ll types are found in the sinusoidal lumen, whereas the majority of ty pe II DC are located in the space of Disse and Glisson's sheath. Furth ermore, some OX6-labeled elongated DC appeared to traverse the lumen o f sinusoids through endothelial pores to enter the space of Disse. One hour after intravenous injection of latex particles (0.81 mu m in dia meter), numerous latex-laden dendritic cells (ED1(+)OX6(+), type I and type I-II) were detected in the lumen of hepatic sinusoids, but not i n the space of Disse or Glisson's sheath. These findings suggest that normal rat liver contains resident dendritic cells which downregulate phagocytic activity and mature into potent accessory cells during migr ation from the portal vein toward the central vein. These DC then trav erse the sinusoidal lumen to the hepatic lymph system via the space of Disse.