Antibody to liver membrane antigens in chronic active hepatitis. IV. Exclusion of specific reactivity to polypeptides and glycolipids by immunoblotting

Asialoglycoprotein receptor (ASGPR) as target autoantigen in liver autoimmunity: lost and found

Asialoglycoprotein receptor (ASGPR) has attracted the attention of liver immunologists for many years. This liver-specific lectin was found to be a major B and T cell autoantigenic target in patients with autoimmune liver diseases, and in particular in autoimmune hepatitis (AIH). This review discusses the biological significance of ASGPR and its relevance to the pathogenesis of autoimmune and virus-triggered liver diseases. We also discuss emerging data on the diagnostic and clinical relevance of anti-ASGPR antibodies in light of recent reports based on commercially available anti-ASGPR enzyme-linked immunosorbent assays. Finally, we critically revisit the data reporting on disease-specific cellular immune responses against ASGPR and their relevance in relation to the pathogenesis of AIH.

Hepatoimmunology: a perspective

Premises for the subspecialty of hepatoimmunology include the recognition that the liver is a lymphoid organ with unique immunological properties. These properties ensure efficient innate defence against intestinal microbes and toxins, confer a particular capacity for induction of tolerance, and provide for apoptotic disposal of redundant lymphocytes. Pathological responses within the liver are elicited when: (i) hepatotropic viruses (hepatitis virus B and C) escape immune elimination and reside in hepatocytes; (ii) the liver becomes the site of autoimmune responses directed against either hepatocytes (autoimmune hepatitis) or biliary ductules (primary biliary cirrhosis); or (iii) the liver in the course of disposal of drugs generates neoantigens that provoke adverse allergic responses. Recent advances in the understanding of the immunopathogenesis of these entities are reviewed.

Xenogeneic antibodies against hepatocyte plasma membranes suppress bile secretion in rats

The action of xenogeneic antibodies against rat hepatocyte plasma membranes which were injected into the portal vein in the dose of 40 mg of protein per kg of body mass on the bile secretion and on the ultrastructure of the liver were studied. It was shown that these antibodies suppressed the bile flow, the secretion of bile acids and cholesterol and decreased the bile salt-independent bile flow. The action of antibodies was accompanied by ultrastructural damage of sinusoidal and lateral plasma membranes of some hepatocytes and by a decrease in the Na+, K(+)-ATPase activity. It was concluded that the decrease of Na+, K(+)-ATPase activity in the plasma membranes was the most important mechanism responsible for a decrease in the bile flow.

Hepatocyte plasma membrane glycosphingolipid reactive with sera from patients with autoimmune chronic active hepatitis: its identification as sulfatide

Sera from patients with autoimmune chronic active hepatitis were found to contain IgG-class antibody to the acidic glycosphingolipid fraction from rabbit hepatocyte plasma membrane by solid-phase enzyme-linked immunosorbent assay. Using serum positive for the antibody as a probe, we isolated the target antigen by Iatrobeads column chromatography. Analysis by thin-layer chromatography and negative ion fast atom-bombardment mass spectrometry revealed that the antigen was sulfatide. The presence of antisulfatide antibody was also confirmed by immunoblotting. The reactivity of the serum with sulfatide was diminished by preincubation of the serum with galactosylceramide-6-sulfate and sulfatide, indicating that the antibody reacted with sulfated galactosylceramide regardless of the position of the sulfate residue. The antibody was found in 92.3%, 42.9%, 15.8%, 14.2%, 0% and 0%, respectively, of patients with autoimmune chronic active hepatitis, primary biliary cirrhosis, cirrhosis, systemic lupus erythematosus, chronic active hepatitis and chronic persistent hepatitis. Thus antisulfatide antibody was characteristic of autoimmune-type chronic liver diseases. Antisulfatide antibody was absorbed by rabbit hepatocyte plasma membrane. Preincubation of sera with sulfatide immobilized on Sepharose decreased their reactivities with not only sulfatide but also rabbit plasma membrane and rat hepatocytes. Therefore sulfatide may be a target antigen of the antibody to hepatocyte surface membrane.

Auto-immune (lupoid) hepatitis: an entity in the spectrum of chronic active liver disease

The concept of auto-immune hepatitis as a disease entity evolved from the descriptions of 'chronic active hepatitis' (CAH) in the 1950s. Several types of CAH are distinguished by disease-specific features. The distinctive (but not exclusive) markers for auto-immune CAH include: a negative test for HBsAg; female; Northern European ethnic background; multisystem disease expression; histological CAH with large areas of periportal piecemeal necrosis and plasmacytosis; pronounced hypergammaglobulinaemia; serum auto-antibodies the HLA B8-DR3 phenotype; responsiveness to corticosteroid therapy; and rarity of supervening hepatocellular carcinoma. Much weight is attached to the serological marker auto-antibodies to nuclear or smooth muscle (actin) antigens (ANA, SMA). However, these auto-antibodies do not have an absolute association with auto-immune CAH: the serological reactions are not yet standardized; titres decrease with remission of disease; and other auto-antibodies mark variant forms of auto-immune hepatitis. A more confident acceptance of auto-immune hepatitis as an entity requires detection of a liver-specific antigen, a valid experimental disease model in animals, and a better understanding of immune-mediated damage to liver cells.

Autoantibodies to isolated human hepatocyte plasma membranes in chronic active hepatitis. II. Specificity of antibodies

The fine specificity of autoantibodies to human hepatocyte plasma membranes in autoimmune chronic active hepatitis was determined by one-dimensional immunoblotting. Sera from 12 patients with "classical" autoimmune chronic active hepatitis contained autoantibodies recognizing many human hepatocyte plasma membrane polypeptides in the 15 to 220 kD range. Many of these autoantibodies titrated beyond 1:80,000 and some may be potentially "pathological." In particular, one band with an apparent molecular weight of 60 kD was a dominant and consistent finding in all patients with autoimmune chronic active hepatitis by immunoblotting. Serum absorption studies showed this band to be predominantly liver-specific. Control sera from patients with chronic persistent hepatitis, nonhepatic autoimmune disease and normal healthy subjects possessed low titer reactivity that most likely represented "natural" autoantibodies. Anti-human hepatocyte plasma membranes in autoimmune chronic active hepatitis consisted of all three immunoglobulin isotypes (G,M and A) and their presence was not caused by nonspecific reactions as a consequence of hypergammaglobulinemia. Autoantibodies were shown to be specific by virtue of their absorption and exhaustion on titration. Many were directed at species nonspecific determinants, however, some autoantibodies recognized human-specific polypeptides. The majority of anti-human hepatocyte plasma membranes appeared to be organ-specific as sera from patients with autoimmune chronic active hepatitis reacted only weakly with polypeptides of kidney plasma membranes. Of the activity detected, few bands corresponded with those obtained using polypeptides of human hepatocyte plasma membranes. Our results show that patients with autoimmune chronic active hepatitis possess an array of liver-specific autoantibodies to polypeptide subunits of human hepatocyte plasma membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoantibodies to human asialoglycoprotein receptor in autoimmune-type chronic hepatitis

Autoantibodies to the human asialoglycoprotein receptor (anti-h-ASGPR) were studied with a solid-phase ELISA in the sera of 421 patients with inflammatory liver diseases, 288 patients with various other disorders and 31 controls. Anti-h-ASGPR were found predominantly in autoimmune chronic active hepatitis (44 of 88, 50%) and were closely related to inflammatory activity. In a subpopulation of these patients with untreated, biopsy-proven active disease or relapse, 15 of 17 were positive (88%). In contrast, only 11 of 204 patients (5.3%) with viral hepatitis were anti-h-ASGPR receptors-positive (chi 2 analysis; p less than 0.001). We also compared the occurrence of anti-h-ASGPR with antibodies to rabbit and rat asialoglycoprotein receptors in 352 sera. In contrast to the anti-human asialoglycoprotein receptor antibodies (3 of 107), anti-rabbit- or anti-rat-asialoglycoprotein receptor antibodies were found in 21 and 28 of 107 cases of viral hepatitis, indicating that different epitopes were recognized by these sera. In various other diseases anti-human asialoglycoprotein receptor antibodies were rarely found. Some sera from patients with connective-tissue diseases (8 of 73) and primary or secondary liver malignancies (6 of 55) exhibited anti-h-ASGPR. In autoimmune chronic active hepatitis the presence of anti-human asialoglycoprotein receptors did not correlate to other established autoantibody systems. Thus we conclude that anti-human asialoglycoprotein receptor antibodies can serve as diagnostic markers for inflammatory active cases of autoimmune chronic active hepatitis. Immune reactions to the asialoglycoprotein receptor, which is expressed on the hepatocellular membrane as a liver-specific antigen, might contribute to the pathogenesis of autoimmune chronic active hepatitis.

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.

Hepatic and biliary autoantigens

Chronic active hepatitis (CAH) and primary biliary cirrhosis (PBC) are two enigmatic liver diseases in which autoimmunity is implicated. Provisional criteria to separate the autoimmune type of CAH (A-CAH) from others are specified. Western immunoblotting using disease sera and antibody screening of a rat liver gene expression library were used to identify hepatic and biliary autoantigens relevant to the pathogenesis of A-CAH or PBC. With all reported putative liver-specific autoantigen preparations, serum reactivity in A-CAH and CAH due to infection with hepatitis B virus tends to be similar. In A-CAH, immunoblotting showed multiple reactivities with all liver preparations used, including hepatocyte membrane. In PBC, immunoblotting showed two disease-specific polypeptide antigens of MW 70 and 45 kD. A cDNA clone derived from a rat liver gene expression library was shown to encode the antigenic site of the 70 kD polypeptide. Recently published work in two other laboratories has established that the 70 kD autoantigen is the E2 component of the pyruvate dehydrogenase enzyme (PDH), and a proposed antibody-binding site (autoepitope) is a conserved decapeptide, corresponding to residues 83-92 of the deduced amino acid sequence of M2, which is the binding site of lipoic acid to the E2 component of PDH.