Anti-liver-kidney microsome antibody is a marker for the rat hepatocyte endoplasmic reticulum.

Human sera, containing anti-liver-kidney microsome antibody as demonstrated by indirect immunofluorescence, were obtained from a subgroup of young patients with autoimmune chronic hepatitis. The anti-liver-kidney microsome antibody-positive sera were used to study the localization of the liver-kidney microsome antigen in hepatocytes. Immunoblot analysis of microsomal subfractions, lysosomal membranes, plasma membranes, mitochondria and purified ribosomes obtained from rat liver demonstrated that this antibody recognizes a protein of 50 kD present only in endoplasmic reticulum membranes. Immunogold labeling of ultrathin frozen sections and immunoperoxidase staining of 11 to 15 micron cryostat sections were used to detect the liver-kidney microsome antigen in rat liver tissue. The anti-liver-kidney microsome antibody binds to antigenic domains on the cytoplasmic face of smooth and rough endoplasmic reticulum membranes of hepatocytes. No labeling was observed of the Golgi apparatus, peroxisomes, mitochondria, lysosomes, nuclei or plasma membranes. Not only was the antigen recognized by the anti-liver-kidney microsome antibody specific for endoplasmic reticulum membranes, but it was also specific for the endoplasmic reticulum of hepatocytes only, since no labeling was observed in any organelle of Kupffer or endothelial cells. Therefore, the anti-liver-kidney microsome antibody can be considered as a marker for endoplasmic reticulum in rat hepatocytes.