Binding sites for endotoxic lipopolysaccharide on the plasma membrane of isolated rabbit hepatocytes

The in vitro fixation of bacterial lipopolysaccharide (LPS) on the plasma membrane of mechanically or enzymatically isolated hepatocytes from rabbits was studied by immunofluorescence technique. Antisera against LPS from E. coli 026:B6 and 0111:B4 were induced in rabbits. Antibody titers up to 1:1024 were determined by the passive hemagglutination test. There was no immunologic cross reactivity between the two antisera. IgG and IgM were prepared from anti-LPS as well as from normal rabbit serum and conjugated with fluorescein-isothiocyanate. The antibody activity against LPS was localized in the IgM fraction. Hepatocytes were isolated by a perfusion technique without enzymes and with collagenase. LPS binding to the hepatocellular plasma membrane increased proportionally with the LPS concentration in a range between 0.01 and 1.0 mg per ml. The fluorescence pattern of the membrane fixed IgM anti-LPS-antibody at the surface of LPS coated hepatocytes was coarse granular. The in vitro reaction of LPS with hepatocytes was not influenced by the presence of complement. The demonstration of binding sites for LPS on the hepatocellular plasma membrane supports the hypothesis that not only Kupffer cells but also parenchymal liver cells are involved in the hepatic clearance activity for endotoxin.