Liver cell damage caused by monoclonal antibody against an organ-specific membrane antigen in vivo and in vitro

Asialoglycoprotein receptor (ASGPR): a peculiar target of liver-specific autoimmunity

Asialoglycoprotein receptor (ASGPR) autoantibodies have been considered specific markers of autoimmune hepatitis (AIH). The exact mechanisms responsible for the development of these autoantibodies and leading to autoimmunity to this peculiar liver receptor remain elusive. Furthermore, loss of T cell tolerance to ASGPR has been demonstrated in patients with AIH, but it is poorly understood whether such liver-specific T cell responses bear a pathogenic potential and/or participate in the precipitation of AIH. Newly developed enzyme-linked immunosorbent assays have led to the investigation of the sensitivity and specificity of anti-ASGPR antibodies for AIH. The present review provides an overview of the diagnostic and clinical relevance of anti-ASGPR antibodies. A thorough investigation of the autoreactivity against ASGPR may assist efforts to understand liver autoimmunity in susceptible individuals.

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.

Pathogenesis of autoimmune hepatitis

Autoimmune hepatitis (AIH) is an idiopathic disorder affecting the hepatic parenchyma. There are no morphological features that are pathognomonic of the condition but the characteristic histological picture is that of an interface hepatitis without other changes that are more typical of other liver diseases. It is associated with hypergammaglobulinaemia, high titres of a wide range of circulating auto-antibodies, often a family history of other disorders that are thought to have an autoimmune basis, and a striking response to immunosuppressive therapy. The pathogenetic mechanisms are not yet fully understood but there is now considerable circumstantial evidence suggesting that: (a) there is an underlying genetic predisposition to the disease; (b) this may relate to several defects in immunological control of autoreactivity, with consequent loss of self-tolerance to liver auto-antigens; (c) it is likely that an initiating factor, such as a hepatotropic viral infection or an idiosyncratic reaction to a drug or other hepatotoxin, is required to induce the disease in susceptible individuals; and, (d) the final effector mechanism of tissue damage probably involves auto-antibodies reacting with liver-specific antigens expressed on hepatocyte surfaces, rather than direct T-cell cytotoxicity against hepatocytes.

Autoimmune hepatitis. Definition--classification--histopathology--immunopathogenesis

Autoimmune hepatitis (AIH) is a distinct form of acute and chronic inflammatory liver disease in which immune reactions against host antigens are found to be the major pathological mechanism. If left untreated it carries an unfavourable prognosis, and the diagnosis should be made as soon as possible. The diagnostic approach has been greatly facilitated by the establishment of a panel of marker autoantibodies, which do not define distinct therapeutic groups of AIH, but do allow a subgrouping based on differences in patient populations, some clinical features and prognosis. The characterization of organ-specific components of the liver cell surface as targets of cellular and humoral autoimmune reactions give new insights into the pathogenesis of the disease, even though the primary event triggering the disease remains to be defined. The most important disease-promoting factor seems to be a genetically determined background for autoimmunity. Without this different environmental factors, including viruses, toxins, cytokines and drugs, are only able to induce transient autoimmune phenomena and not autoimmune disease. The histopathology of AIH is in keeping with the present pathogenetic concept. Although there is no pathognomonic feature distinguishing this type of hepatitis from virus-induced forms, some distinct morphological lesions are regarded as characteristic. Clinical research on AIH has benefited greatly from observations of experimental AIH in mice. Recognition of the critical role of autoreactive T-lymphocytes in the pathogenesis and the observation of spontaneous recovery from AIH in the animal model associated with antigen-specific and antigen-non-specific T-cell suppression have made basic contributions to our improved understanding of the natural course of AIH in humans.

The human hepatic asialoglycoprotein receptor is a target antigen for liver-infiltrating T cells in autoimmune chronic active hepatitis and primary biliary cirrhosis

Autoantibodies to the human hepatic asialoglycoprotein receptor have been found in nearly 50% of the sera of patients with autoimmune chronic active hepatitis and in 15% of patients with primary biliary cirrhosis. In this study we demonstrate that the human hepatic asialoglycoprotein receptor is also a target antigen for T cell-mediated immune responses. Peripheral blood lymphocytes of 37% (7 of 19) of patients with autoimmune chronic active hepatitis and 33% (2 of 6) of patients with primary biliary cirrhosis showed a proliferative response to highly purified human hepatic asialoglycoprotein receptor, whereas no proliferation was found with peripheral blood lymphocytes of patients with chronic viral hepatitis (0 of 13) and healthy blood donors (0 of 4). Moreover, we isolated T-cell clones from liver biopsy samples of two patients with autoimmune chronic active hepatitis and two patients with peripheral blood lymphocytes. Between 2.8% and 14.3% of these clones showed a specific proliferative response to purified human hepatic asialoglycoprotein receptor. The response was restricted to autologous antigen-presenting cells and could be blocked by monoclonal antibodies against human leukocyte antigen-DR molecules. The response of T cells to the human hepatic asialoglycoprotein receptor did not require the lectinlike activity of the asialoglycoprotein receptor. Thus the human hepatic asialoglycoprotein receptor could be identified as a major target antigen of humoral and cellular immune reactions in autoimmune-mediated liver diseases.

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.

Antibodies against the hepatic asialoglycoprotein receptor perfused in situ preferentially attach to periportal liver cells in the rat

Autoantibodies reacting with the galactose-specific hepatic asialoglycoprotein receptor--a liver-specific component expressed on the surfaces of hepatocytes--are often found in patients with chronic active hepatitis of presumed autoimmune origin. As part of an investigation into whether these anti-asialoglycoprotein receptor antibodies might be involved in the development of periportal liver damage in chronic active hepatitis, livers of ether-anesthetized rats were perfused in situ with polyclonal guinea pig anti-rabbit asialoglycoprotein receptor or murine monoclonal anti-human galactose-specific hepatic asialoglycoprotein receptor antibodies in excess at less than 8 degrees C or, as a control, with guinea pig anti-human plasma protein antibodies or normal guinea pig serum. Rapid (1 min) antegrade (by way of portal vein) or retrograde (through hepatic veins by way of vena cava) perfusions were performed in a nonrecirculating (once-through) mode in Ca+(+)-free medium. Blocks of liver tissue were immediately snap-frozen and the distribution of the antibody examined in cryostat sections by using an avidin-biotin immunohistochemical technique. In all of the perfusions with anti-asialoglycoprotein receptor (six antegrade, seven retrograde), the antibodies were found to be prominently and almost exclusively deposited on liver cells in the periportal areas. No deposition of immunoglobulins was detected in livers perfused with the control guinea pig sera. The findings suggest that the asialoglycoprotein receptor is expressed at high density mainly on cells in zone 1 of the hepatic lobule, and this may have implications for the development of periportal liver damage in chronic active hepatitis.

Anti-HBs- and anti-HBc-containing plasma cells in livers of patients with chronic type B hepatitis

Plasma cells are commonly found in liver biopsies in acute and chronic type B hepatitis. Their specificities have not hitherto been examined. In this study, anti-HBs and anti-HBc were looked for in paraffin sections of liver biopsies from 16 patients with chronic type B hepatitis, all seropositive for HBeAg. The technique used was a reversed immunoperoxidase procedure in which purified antigens were applied to sections and detected by means of a further layer of the appropriate monoclonal antibody. Small numbers of plasma cells stained for anti-HBs and anti-HBc in 6 and 4 of 16 biopsies, respectively. Some plasma cells appeared to contain neither antibody. The two antibodies were detected together in only one biopsy. In spite of the small numbers of positive cells as revealed by the technique used, antiviral antibodies produced locally by plasma cells may play a part in the pathogenesis of viral hepatitis.