Liver Cell Uptake and Degradation of Soluble Immunoglobulin G Immune Complexes In Vivo And In Vitro In Rats

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Abstract
Immune complexes were formed between dinitrophenylated human serum albumin (DNP–HSA) and polyclonal rabbit immunoglobulin G (IgG) anti–DNP antibodies at antibody excess. The antigen was labelled with isotope (125I–tyramine–cellobiose) or fluorochrome, (6–[fluorescein–5–(and–6)–carboxamido] hexanoic–acid, succinimidyl ester). The radiolabelled antigen, native or antibody complexed, was given intravenously to rats. Radioactivity was measured in various organs at 1 hour following injection. The liver was the main site for removal of the antigen as well as of the immune complexes. Within the liver, immune complexes were mainly associated with nonparenchymal liver cells, the total recovery from Kupffer cells being about 10 times greater than from the liver endothelial cells. The uncomplexed radiolabelled antigen was readily degraded by both cells types. After IgG complexing, the degradation decreased, both in Kupffer cells and in liver endothelial cells. In vitro experiments with isolated liver cells, showed that IgG complexing increased antigen uptake to about the same extent in Kupffer cells and in liver endothelial cells. The degradation of both antigen and immune complexes was less efficient in vitro than in vivo . Immune complex uptake in vitro was shown also by confocal fluorescence microscopy in Kupffer cells and in liver endothelial cells. Also in vitro , only minor uptake was found in the hepatocytes. We conclude that both liver endothelial cells and Kupffer cells are involved in the hepatic handling of soluble IgG immune complexes, but we found no evidence for substantial uptake by hepatocytes.