Abstract
The uptake of formalin-denaturated homologous albumin (FDA) by rat liver sinus-lining cells was studied using ultrastructural, cyto-chemical, and immunocytochemical techniques. Three minutes after intra-venous injection of: 1) FDA, 2) peroxidase-coupled FDA (HRP-FDA), 3) ferritin-labeled FDA (FE-FDA), 4) colloidal gold-labeled FDA (CG-FDA), or 5) 0.85 % NaCl, livers were fixed by perfusion with two different fixatives. Liver sections were processed to cytochemical, immunocytochemical, or immunoelectron microscopical procedures. By light microscopic immuno-cytochemistry (groups 1 and 5), discrete granular staining was seen in endo-thelial cells, Kupffer cells, and parenchymal cells. Whereas the staining in endothelial cells and Kupffer cells was much weaker in group 5 than in group 1, no difference was noted in parenchymal cells between the two groups. By immunoelectron microscopy, albumin was localized in coated pits, coated ve-sicles, endosomes, and phagosomes of endothelial cells and Kupffer cells. In parenchymal cells, however, albumin was confined exclusively to the secretory apparatus. In group 2 (HRP-FDA) the reaction product was localized only in coated pits, vesicles, and endosomes of endothelial cells and Kupffer cells, but not in parenchymal cells. Similarly, in animals injected with FE-FDA and CG-FDA, the ferritin and gold particles were found exclusively in the same intracellular compartments of the sinus-lining cells. The results strongly suggest that FDA is internalized by endothelial cells and Kupffer cells through a receptor-mediated endocytosis.
