Liver membrane antibodies (LMA) recognize a 26-kD protein on the hepatocellular surface

Sera from 82 patients with chronic inflammatory liver diseases and from patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and Hashimoto's thyroiditis were studied by immunoblotting against purified liver plasma membranes (LPM) and soluble liver protein (SLP) fractions from different species after previous separation by SDS-PAGE. Eighteen of 19 sera with LMA of IgG type in immunofluorescence assay and six LMA-negative sera (three sera from patients with RA) showed antibodies of the IgG or IgM classes against a protein with a molecular weight of 26 kD which was present in LPM and SLP fractions from rats, rabbits, pigs and humans. The reaction with 26-kD liver protein did not correlate with other known autoantibody-antigen systems. All sera were negative in the 26-kD region with liver mitochondria, liver microsomes and soluble proteins of kidney (with one exception), heart and gut from the rat. The 26-kD protein was purified by affinity chromatography on immobilized anti-26-kD protein antibodies from patients, eluted from the 26-kD band of immunoblots. Studies with purified 26-kD liver protein and with SLP as antigens after separation in two-dimensional electrophoresis confirmed that patient serum and experimental rabbit antiserum react with the same protein. Eluted patient antibodies and rabbit antisera showed a linear fluorescence pattern on isolated hepatocytes from rat and rabbit. The data indicate that one of the target antigens of LMA is a species-nonspecific 26-kD protein located on the hepatocellular surface.