Uptake of formalin-denaturated albumin by the sinus-lining cells of rat liver: an immunocytochemical and cytochemical study.

The uptake of formalin-denaturated homologous albumin (FDA) by rat liver sinus-lining cells was studied using ultrastructural, cytochemical, and immunocytochemical techniques. Three minutes after intravenous 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 immunocytochemistry (groups 1 and 5), discrete granular staining was seen in endothelial 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 vesicles, 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.