T-lymphocyte sensitization to hepatocyte antigens in autoimmune chronic active hepatitis and primary biliary cirrhosis. Evidence for different underlying mechanisms and different antigenic determinants as targets

Role of regulatory T cells in inflammatory liver diseases

The liver is the human body's largest digestive gland, which can participate in digestion, metabolism, excretion, detoxification and immunity. Chronic liver diseases such as metabolic dysfunction-associated fatty liver disease (MAFLD) or viral hepatitis involve ongoing inflammation and resulting liver fibrosis may ultimately lead to the development of hepatobiliary cancers (HCC). Inflammation is the coordinated reaction of different liver cell types to cell signals and death of inflammation, which are linked to injury pathways within the liver or external agents from the gut-liver axis and the circulation. Regulatory T (Treg) cells play a crucial role in controlling inflammation and are essential for maintaining immune tolerance and balance. In this review, we highlight the recent discoveries related to the function of immune systems in liver inflammation and discuss the role of Treg cells in the different liver diseases (including MAFLD, autoimmune hepatitis and others).

Regulatory T cells in autoimmune hepatitis: an updated overview

Regulatory T-cells (Tregs) are key players in the maintenance of immune homeostasis by preventing immune responses to self-antigens. Defects in Treg frequency and/or function result in overwhelming CD4 and CD8 T cell immune responses participating in the autoimmune attack. Perpetuation of autoimmune damage is also favored by Treg predisposition to acquire effector cell features upon exposure to a proinflammatory challenge. Treg impairment plays a permissive role in the initiation and perpetuation of autoimmune liver diseases, namely autoimmune hepatitis, primary biliary cholangitis and primary sclerosing cholangitis. In this Review, we outline studies reporting the role of Treg impairment in the pathogenesis of these conditions and discuss methods to restore Treg number and function either by generation/expansion in the test tube or through in vivo expansion upon administration of low dose IL-2. Challenges and caveats of these potential therapeutic strategies are also reviewed and discussed.

Regulatory T-cells in autoimmune diseases: challenges, controversies and--yet--unanswered questions

Regulatory T cells (Tregs) are central to the maintenance of self-tolerance and tissue homeostasis. Markers commonly used to define human Tregs in the research setting include high expression of CD25, FOXP3 positivity and low expression/negativity for CD127. Many other markers have been proposed, but none unequivocally identifies bona fide Tregs. Tregs are equipped with an array of mechanisms of suppression, including the modulation of antigen presenting cell maturation and function, the killing of target cells, the disruption of metabolic pathways and the production of anti-inflammatory cytokines. Treg impairment has been reported in a number of human autoimmune conditions and includes Treg numerical and functional defects and conversion into effector cells in response to inflammation. In addition to intrinsic Treg impairment, resistance of effector T cells to Treg control has been described. Discrepancies in the literature are common, reflecting differences in the choice of study participants and the technical challenges associated with investigating this cell population. Studies differ in terms of the methodology used to define and isolate putative regulatory cells and to assess their suppressive function. In this review we outline studies describing Treg frequency and suppressive function in systemic and organ specific autoimmune diseases, with a specific focus on the challenges faced when investigating Tregs in these conditions.

CD4+ CD25+ regulatory T cells: a therapeutic target for liver diseases

BACKGROUND

Regulatory T cells (Tregs) have been shown to play an important role in maintaining peripheral immune homeostasis by suppressing autoreactive and allergen-specific T cells and turning off the immune response after the pathogen has been cleared. However, in certain situations Tregs can impair effective immunity to some pathogens and tumour cells.

OBJECTIVE

To review the role of Tregs in liver pathology and to assess the potential to enhance or inhibit their function as applied to the treatment of liver disease.

METHODS

The literature was reviewed using standard indexing terms and incorporating publications up to and including those published in 2007.

RESULTS/CONCLUSIONS

Tregs are therapeutic targets for modulation in autoimmune disease and may provide new opportunities for application to human liver conditions.

Analysis of CD28 and bcl-2 Expression on Peripheral Blood and Liver-Infiltrating Mononuclear Cells in Patients with Autoimmune Hepatitis

Because the underlying mechanism of hepatocellular damages in autoimmune hepatitis (AIH) still remains unclear, analysis of CD28 and bcl-2 molecules, which are critical for T cell activation and survival, was performed in patients with AIH. The number of CD28(+)CD4(+) peripheral blood mononuclear cells (PBMC) in corticosteroid (CS)-treated patients was comparable to normal control individuals but decreased in untreated AIH patients. In contrast, the number of CD28(+)CD8(+) PBMC was decreased in both CS-treated and untreated AIH patients. Analysis of liver-infiltrating mononuclear cells (LIMC) showed that the number of CD28(+)CD4(+) and CD28(-)CD8(+) LIMC were positively correlated with the histology activity index score. Bcl-2(+)CD4(+) LIMC were observed in the portal area of the liver and the numbers fluctuated with disease activity during the time course after CS administration. By contrast, CD8(+) LIMC were shown not to express bcl-2. Taken collectively, these results suggest that bcl-2(+)CD28(+)CD4(+) and bcl-2(-)CD28(-)CD8(+) cells may play critical and distinct roles in hepatocellular damage in 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.

Immunohistochemical characterization of the lesions of feline progressive lymphocytic cholangitis/cholangiohepatitis

The histopathological features of liver biopsies from 20 cats with progressive lymphocytic cholangitis/cholangiohepatitis are reported. These biopsies were subject to immunohistochemical investigation for expression of CD3, CD79. Major Histocompatibility Complex (MHC) Class II molecules, and feline IgG, IgM and IgA. Livers from five normal cats, which were also examined showed constitutive expression of MHC Class II by sinusoidal Kupffer cells and bile duct epithelium, in addition to a population of portal, and bile duct inter-epithelial, CD3+ T lymphocytes. In liver biopsies from cats with the active phase of lymphocytic cholangitis/cholangiohepatitis (n = 11), the portal lymphocytes were predominantly CD3+ T cells that infiltrated bile duct epithelium and periportal hepatic parenchyma, CD79+ B lymphocytes formed distinct aggregates or follicles within the regions of T-cell infiltration. Low numbers of plasma cells were present, and these predominantly expressed IgA. MHC Class II was expressed by Kupffer cells, infiltrating T and B lymphocytes and macrophages. There was membrane and cytoplasmic Class II expression by bile duct epithelium, some vascular endothelium, and fibroblasts within areas of fibrosis. In liver biopsies from cats with chronic lymphocytic cholangitis/cholangiohepatitis (n = 9), there was less in flammation, but the composition of the infiltrates was similar to that in the active phase of disease. The findings provide further evidence for an immune mediated pathogenesis in progressive lymphocytic cholangitis/cholangiohepatitis.

Cell-mediated immune responses to liver membrane protein in canine chronic hepatitis

Peripheral blood mononuclear cells from dogs with chronic inflammatory liver disease and dogs with noninflammatory liver diseases were evaluated for proliferative responses to pokeweed mitogen and canine liver membrane protein. Dogs with chronic hepatitis were selected based on histopathological evidence of periportal lymphocytic infiltrates with or without neutrophilic infiltrates, fibrosis and necrosis. Incorporation of tritiated thymidine was assessed 72 hours after addition of liver membrane protein or pokeweed mitogen. Peripheral blood mononuclear cell proliferation in response to liver membrane protein was significantly higher in chronic hepatitis dogs compared to control dogs. Eight of 12 dogs with chronic hepatitis and 2 of 7 dogs with noninflammatory liver disease had proliferative responses to liver membrane protein greater than 2 standard deviations above the mean of the control group. These data support the hypothesis that immune-mediated processes are involved in canine chronic hepatitis, but did not determine whether this is a primary disorder or occurred secondary to liver destruction.

Immunoglobulin-A and the pathogenesis of schistosomal glomerulopathy

Several observations suggest that the evolution of schistosomal glomerulopathy into clinically overt and progressive disease may involve pathogenetic mechanisms other than simple glomerular deposition of parasitic antigens. In a previous study, IgA was suggested to be a mediator of late glomerular lesions in this disease. This issue is further addressed in this work. The study includes 32 patients with hepatosplenic schistosomiasis, of whom 16 had overt glomerular involvement, along with four control groups: (a) 15 healthy volunteers; (b) 15 patients with simple intestinal mansoniasis; (c) 17 patients with non-schistosomal chronic liver disease; and (d) 21 subjects with primary nephrotic syndrome not associated with schistosomiasis. Routine assessment was done for all subjects including confirmatory tests for schistosomal infection, liver and renal function tests, hepatitis viral markers and abdominal ultrasonography. The total serum concentrations of IgG, IgM, IgA were measured, as well as their respective circulating immune complexes, rheumatoid factors, anti-gliadin- and anti-DNA-antibodies. Liver and renal biopsies were obtained from the relevant groups and studied by light microscopy. Renal biopsies were also examined by immunofluorescence. Patients with simple intestinal schistosomiasis had a significant increase in IgM antigliadin antibodies. Those complicated with hepatosplenic involvement also had a significant increase in the mean IgG anti-gliadin antibodies, IgG rheumatoid factor and IgM anti-DNA activity. Cases further complicated by overt glomerular disease showed a distinct IgA predominance, mainly expressed in the serum anti-gliadin antibody pool and anti-DNA activity. This profile was essentially similar to that observed in control cirrhotics. There was a significant increase in the frequency of IgA glomerular deposits in renal biopsies obtained from patients with overt schistosomal glomerulopathy, in contrast to control nephrotics. The deposits were mainly mesangial, but were also encountered in subendothelial, subepithelial and peritubular locations. Their frequency was significantly higher with more advanced lesions as seen by light microscopy. The relevance of these data is discussed, leading to the following conclusions: (a) serum IgA-anti-gliadin and -anti-DNA antibodies, and glomerular IgA deposits are markers of significant renal involvement in patients with hepatosplenic schistosomiasis. (b) IgA may be involved in the pathogenesis of advanced glomerular pathology when superimposed on parasite-induced lesions. (c) There is a significant increase in serum auto-reactivity in hepatosplenic schistosomiasis, which may also have pathogentic implications. (d) Increased production by the inflammatory bowel lesions, impaired clearance by the fibrotic livers and probable switching of immunoglobulin synthesis are suggested to explain the observed IgA predominance in those who develop renal complications.

Cellular and humoral immune reactions against autoantigens and hepatitis C viral antigens in chronic hepatitis C

BACKGROUND/AIMS

Previous reports have suggested that the hepatitis C virus (HCV) may induce autoimmune hepatitis. The aim of this study was to examine this hypothesis by investigating humoral and cellular immune responses to HCV-related antigens and various autoantigens in patients with chronic HCV infections.

METHODS

Lymphoproliferative responses in vitro and/or circulating antibodies to an HCV core peptide, the putative autoantigen GOR, the liver-specific hepatic asialoglycoprotein receptor (ASGP-R), and other autoantigens were investigated in 27 adults with chronic hepatitis C.

RESULTS

Five patients with HCV (18.5%) showed cellular immune responses to ASGP-R and two others had antibodies to ASGP-R, whereas 6 of 14 patients (42.8%) showed cellular responses to GOR and 7 of 14 patients (50%) showed responses to HCV core. Other autoantibodies were detected in three patients (11%). Nine patients with autoimmune hepatitis studied concurrently for comparison showed cellular and/or humoral responses to ASGP-R but not to GOR. Only 2 of 11 patients with other chronic liver disorders showed immune responses to any antigen tested.

CONCLUSIONS

Specific immunocompetence against HCV-related antigens can often be shown in patients with chronic hepatitis C but is infrequently accompanied by autoreactions against liver-specific or nonspecific antigens. A reported association between T-cell responses to HCV core and lack of liver damage could not be confirmed.

T-cell receptor constant beta germline gene polymorphisms and susceptibility to autoimmune hepatitis

BACKGROUND/AIMS

Susceptibility to autoimmune hepatitis is associated with HLA A1-B8-DR3 and DR4. T-Cell antigen receptors (TCR) are candidates for genetic susceptibility to autoimmune diseases because they recognize peptide antigens in the context of HLA molecules. The aim of this study was to investigate the possible role of TCR germline polymorphisms in susceptibility to autoimmune hepatitis.

METHODS

TCR constant beta (C beta) region polymorphisms were investigated using restriction fragment length polymorphism analysis in 60 unrelated northern European White patients with autoimmune hepatitis and 190 racially and geographically matched healthy controls.

RESULTS

A significant increase in the frequency of homozygous status for the 10-kilobase/Bgl II of the TCR C beta was found in the patients compared with controls (42% vs. 21%; corrected P value [Pc] < 0.0075; relative risk [RR] = 2.8). This difference was more pronounced in patients without HLA-DR3 and DR4 (50% vs. 14%; Pc < 0.015; RR = 6.1). Furthermore, heterozygosity for TCR C beta was significantly decreased in early-onset patients presenting with HLA-DR3 before 30 years of age (12% vs. 48%; Pc < 0.03; RR = 0.16).

CONCLUSIONS

The present findings provide evidence that genetic susceptibility to AIH may be determined by both the TCR C beta genes and HLA genes and that the genotype of the TCR C beta may be one of the factors in influencing the age at onset of disease.

T and B cell responses to neutrophil cytoplasmic antigens in systemic vasculitis

The systemic vasculitides (SV) are characterized by the presence of autoantibodies to neutrophil cytoplasmic antigens (ANCA). The role of T cells in SV is uncertain. We studied human and murine T cell responses to human neutrophil cytoplasmic antigens in vitro. T cells from mice immunized with the neutrophil extract showed dose-dependent antigen-specific proliferation, restricted by the MHC class II E molecule. Myeloperoxidase (MPO) was not an important target antigen for murine T cells. Peripheral blood lymphocytes (PBLs) were obtained from 36 patients with SV, 31 before the start of immunosuppressive therapy, and from 11 healthy controls. T cell responses to the neutrophil extract in vitro did not differ between patients and controls: there were only low levels of antigen-specific proliferation, and this could not be amplified by in vitro selection. In 3 patients and 2 normals, PBLs were also tested after the depletion of CD8+ cells; this did not unmask T cell reactivity to neutrophil extract. The lack of demonstrable T cell reactivity to this antigen preparation may indicate that T cells do not play an important effector role in these diseases. A solid-phase spot ELISA was adapted to demonstrate autoantibody-producing B cells in vitro. Low numbers of ANCA-producing B cells could be demonstrated in the majority of patients. B cells producing antibody to MPO could be demonstrated in most patients and in three laboratory staff, but not in normals from outside the laboratory. In 2 patients, sequential B cell spot ELISAs were performed during the introduction of therapy, and autoantibody-producing B cells rapidly decreased in number. This assay may therefore be useful in monitoring the effects of treatment at the cellular level.

Liver-infiltrating T helper cells in autoimmune chronic active hepatitis stimulate the production of autoantibodies against the human asialoglycoprotein receptor in vitro

Autoantibodies against the human asialoglycoprotein receptor (ASGPR) occur in the sera of patients with autoimmune liver disorders. Liver-infiltrating T cell clones that specifically recognize the ASGPR have been described in patients with autoimmune chronic active hepatitis (AI-CAH) and primary biliary cirrhosis (PBC). Recently, we have shown that peripheral blood mononuclear cells (PBMC) from patients with AI-CAH or PBC but not chronic viral hepatitis secreted anti-ASGPR antibodies in vitro. In this study we characterized the influence of liver-infiltrating T cells on the secretion of ASGPR-specific autoantibodies by autologous B cells in cell culture supernatants. T cell clones from liver biopsies of three patients with chronic autoimmune liver disorders (one with AI-CAH, two with PBC) were isolated and investigated for their proliferative response to soluble ASGPR and their helper function provided to autoantibody-secreting B lymphocytes. PBMC from these patients secreted autoantibodies spontaneously in their cell culture supernatants and showed a proliferative response to ASGPR. T cell-depleted PBMC, however, lacked spontaneous antibody secretion. Four CD4+CD8- liver-infiltrating T cell clones showed a proliferative response to ASGPR and also induced spontaneous anti-ASGPR antibody production in cell culture supernatants when added to autologous T cell depleted PBMC. Activated supernatants of these T cell clones failed to induce antibody production. None of seven CD4+CD8- and two CD4-CD8+ T cell clones non-responding to ASGPR provided this help for antibody secretion. Anti-ASGPR secretion in vitro could not be inhibited by the addition of MoAbs raised against monomorphic determinants on HLA class II molecules. The addition of purified ASGPR or polyclonal-activating pokeweed mitogen showed no influence on the production of autoantibodies in these cultures. These data show that B lymphocytes require T cell help for the production of ASGPR-specific antibodies. This help can be provided by ASGPR-responsive T helper cells via cellular interactions.

Blood and liver-infiltrating lymphocytes in primary biliary cirrhosis: increase in activated T and natural killer cells and recruitment of primed memory T cells

We used two-color and three-color flow cytometric analysis to study phenotypical activation and functional subsets of T and natural killer cells in the blood and liver tissue of patients with primary biliary cirrhosis, other chronic liver diseases and the blood of healthy subjects. The changes in blood lymphocyte phenotype in patients with primary biliary cirrhosis and other chronic liver diseases were similar and comprised elevated relative or absolute numbers of activated human leukocyte antigen-DR + T subset (CD4+ and CD8+) cells and DR+ natural killer-like (CD16+) cells. B cell (CD19+) numbers were normal. In primary biliary cirrhosis a selective reduction in T cells of suppressor-inducer (CD45RA + CD4 + ) type was registered. The human leukocyte antigen-DR expression among CD4+ T cell subsets was investigated further in primary biliary cirrhosis and healthy controls using triple antibody flow cytometric analysis. Phenotypical cell activation was confined to helper T cells of the primed, memory (CD45RO + CD4+) type. The decrease in suppressor-inducer T cells in primary biliary cirrhosis was paralleled by a reciprocal increase in primed memory T cells. Several significant differences were observed when blood and liver-infiltrating cells from primary biliary cirrhosis patients were compared. In the liver tissue, the CD4/CD8 ratio was decreased, the relative activation of T-subset cells and NK cells was further increased, the suppressor-inducer T subset was further depressed and the primed memory T subset was increased. The cytotoxic T-cell subset (CD11b-) dominated within the CD8+ population. In liver tissue from other chronic liver disease subjects, a lower CD4/CD8 ratio was found compared with primary biliary cirrhosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Susceptibility to autoimmune chronic active hepatitis: human leukocyte antigens DR4 and A1-B8-DR3 are independent risk factors

After nearly 18 years of research, the association between human leukocyte antigens A1-B8-DR3 and autoimmune chronic active hepatitis still provokes debate. The principal reasons for this are disease heterogeneity and racial variation in the distribution of human leukocyte antigens between populations. The aim of the present study was to reexamine the relationship between these antigens and autoimmune chronic active hepatitis in a well-characterized series of patients. Ninety-six outpatients with autoimmune chronic active hepatitis and an additional 14 referred for liver transplantation with end-stage autoimmune chronic active hepatitis were studied. Human leukocyte antigen frequencies were compared with those of 100 racially and geographically matched controls. The A1-B8-DR3 haplotype was present in 38% of patients compared with 11% of controls (chi 2 = 20.6, p less than 0.0005). When all the DR3-positive patients were eliminated, there was a striking secondary association with DR4; 35 (80%) of 44 remaining patients were DR4 positive compared with 31 (39%) of 79 DR3-negative controls (Fisher's exact probability test p = 0.000031, pc = 0.0013). In addition patients with A1-B8-DR3 are seen at a significantly younger age than those without (39.75 yr vs. 48.21 yr, p less than 0.025), relapse more frequently (52% of patients with A1-B8-DR3 relapsed on one or more occasions compared with 34% of patients without this haplotype) and are more frequently referred for liver transplantation. These data indicate for the first time that two genes within the major histocompatibility complex closely linked to the DR3 and DR4 genes independently confer susceptibility to autoimmune chronic active hepatitis.

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.

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.

Immunohistochemical demonstration of the asialoglycoprotein receptor in rat liver by a sensitive avidin-biotin technique

An immunohistochemical technique for the detection of the hepatic asialoglycoprotein receptor (ASGP-R) in cryostat sections of liver by polyclonal and monoclonal anti-ASGP-R antibodies is described. The procedure is based on the alkaline-phosphatase-avidin-biotin complex (ABC-AP) system and important features include fixation of the sections with periodate-lysine-paraformaldehyde (with or without dichromate) and an absolute requirement for blocking of endogenous biotin activity. The sensitivity of the technique is such that binding to ASGP-R can be detected with femtomolar concentrations of monoclonal anti-ASGP-R antibodies and, with polyclonal antisera, approaches that of a radioimmunoassay.

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.

Production of murine monoclonal antibodies against a liver-specific, species cross-reactive antigen in the liver-specific lipoprotein (LSP) preparation

Previous attempts in several laboratories have failed to produce murine monoclonal antibodies (MAbs) against liver-specific, species-cross-reactive, cell surface-expressed antigens in the normal liver preparation known as liver-specific membrane lipoprotein (LSP). In the present study, BALB/c mice were pretreated with a single dose of cyclophosphamide (20 mg/kg), hyperimmunized with human LSP and hybridomas produced by fusion of spleen cells from these mice with murine myeloma (P3-NS1-Ag4-1) cells. To bias selection in favour of MAbs reacting with species cross-reactive epitopes, hybridoma supernatants were screened by ELISA against rabbit LSP. From 70 stable hybridomas, four MAbs were obtained that react with rabbit LSP. One is an IgM antibody and the other three are of IgG2a class. All four react with the hepatic asialo-glycoprotein receptor (HL), a liver-specific, species-cross-reactive component that is normally expressed on the surfaces of hepatocytes. Using a rapid screening technique (an 'additive' ELISA), preliminary evidence was obtained indicating that these four MAbs between them recognise three different epitopes on the HL molecule. The results suggest that this is a viable approach for the production of MAbs against autoantigens to which autoreactivity may normally be suppressed.

Sensitive avidin biotin based technique for identifying liver membrane antigens in tissue sections

An enzyme immunohistochemical technique for the localisation of liver membrane antigens in tissue sections by antisera raised in guinea pigs against the liver preparation known as "liver specific membrane lipoprotein (LSP)" was developed, based on the alkaline phosphatase avidin biotin complex (ABC AP) system. Of a wide range of fixatives and fixation conditions investigated, a short (five minute) exposure of cryostat sections to Bouin's fluid provided the most satisfactory results and--together with procedures to block endogenous biotin and alkaline phosphatase--yielded clear sections with no background staining or other artefacts to interfere with specific staining patterns. The sensitivity of the technique approaches that of a radioimmunoassay, as shown by the staining of the sinusoidal domains of hepatocellular plasma membranes by the guinea pig anti-LSP antisera at dilutions up to 1/50,000. Apart from its reliability and sensitivity the procedure offers additional advantages over techniques such as indirect immunofluorescence in that it provides a permanent preparation with well defined morphological details which can be seen by ordinary light microscopy.

Pathologic analysis of liver transplantation for primary biliary cirrhosis

A retrospective histopathologic review of all pathologic specimens from 394 adult liver transplant patients was undertaken with clinical correlation to determine if primary biliary cirrhosis has affected the posttransplant course compared to all other indications for liver transplantation and if recurrent primary biliary cirrhosis has occurred after liver transplantation. We also compared the histopathologic features seen in native livers with primary biliary cirrhosis to failed allografts with chronic rejection. One hundred six of the 394 adult patients transplanted during this time (1981 to July, 1986) fulfilled clinicopathologic criteria for a diagnosis of primary biliary cirrhosis. Neither the incidence nor any qualitative pathologic feature of histologically documented acute cellular rejection differentiated subjects transplanted for primary biliary cirrhosis vs. other diseases. No correlation between the titers of antimitochondrial antibody and the presence of posttransplant hepatic dysfunction based on liver enzyme profiles or the development of chronic rejection was seen in patients transplanted for primary biliary cirrhosis. Minor differences noted in the posttransplant course of primary biliary cirrhosis patients as compared to other conditions (higher incidence of chronic rejection as a cause of graft failure) was seen, but this did not significantly affect graft or patient survival. Recurrent primary biliary cirrhosis could not be diagnosed with certainty in any patient. A comparison of failed chronically rejected allografts vs. native hepatectomies obtained from patients with primary biliary cirrhosis revealed the presence of chronic obliterative vasculopathy, centrilobular cholestasis, and lack of granulomas, cirrhosis, cholangiolar proliferation, copper-associated protein deposition and Mallory's hyalin in specimens with chronic rejection.(ABSTRACT TRUNCATED AT 250 WORDS)

Serial study of liver-directed autoantibodies and autoreactive T-lymphocytes in acute viral hepatitis B

To explore the mechanisms underlying liver-directed autoimmune reactions in acute Hepatitis B Virus (HBV) infection, we followed five subjects who were identified in the early incubation phase (30-70 days before the first elevation of transaminases). We assessed serially cellular (using a T-lymphocyte migration inhibitory factor assay) and humoral (RIA) immunity to LSP (a macromolecular, liver-derived lipoprotein complex) and hepatic lectin (HL), the liver-specific receptor for desialylated glycoproteins, which appears to be a major target antigen for autoreactions in autoimmune chronic active hepatitis. Anti-LSP and anti-HL autoantibodies were found, at some stage during acute HBV infection, in 4/5 subjects, whereas cellular immunity to the same antigens was detected in only two patients. Sustained production of anti-HL antibodies was noted only in patients showing cellular immunity to this antigen and was apparently secondary to liver damage, whereas anti-LSP antibodies were first detected at the onset of liver injury when there was no evidence of T-cell immunity to the same antigenic complex. One explanation for this apparent dichotomy between cellular and humoral responses to LSP is that a helper T-cell response to the major envelope component of HBV, HBsAg, which precedes by 10-20 days the development of anti-LSP antibodies, promotes a humoral reaction to autoantigens contained in the LSP preparation, coexpressed with HBsAg, on the surface of infected hepatocytes.

Monoclonal antibodies identifying antigens on distinct domains of rat hepatocytes

To aid in evaluating the functional significance of various domains of the hepatocyte plasma membrane, we have developed monoclonal antibodies that react with three different antigens on the surface of rat hepatocytes. One antigen is present on the sinusoidal-lateral plasma membrane but is absent from the bile canalicular membrane. On the basis of apparent molecular weight and ability to bind a desialylated glycoprotein, this antigen may be the asialoglycoprotein receptor. It was also identified immunocytochemically on the sinusoidal-lateral plasma membrane of human hepatocytes. The second antigen is present only on the bile canalicular membrane, whereas the third is present on the entire cell surface of rat hepatocytes. Our monoclonal antibodies may be useful in investigations of the sorting mechanisms of hepatocyte membrane proteins and the pathogenesis of certain liver diseases.

Prospective study of cellular immunity to hepatitis-B-virus antigens from the early incubation phase of acute hepatitis B

Cellular immunity to hepatitis-B-virus (HBV) antigens was followed prospectively in five patients who were identified in the early incubation phase of acute HBV infection, between 30 and 70 days before the onset of liver damage. Cellular immunity to pre-S antigens was the first detectable immune response, appearing 30 days before the first rise in serum aminotransferases in every case. T-cell sensitisation to HBcAg followed, with IgM anti-HBc appearing 10 days later. A cellular immune response to HBsAg was the last to appear, 10 days before the onset of liver damage. These cellular immune responses are the earliest host responses to the virus infection and could be critical in initiating and directing the processes of liver damage and viral clearance.

T-cell inducers of suppressor lymphocytes control liver-directed autoreactivity

The sensitisation of helper T cells of patients with autoimmune chronic active hepatitis to a liver-cell membrane-expressed asialoglycoprotein receptor protein is shown to be associated with a defect of T cells that specifically induce suppressor lymphocytes. These lymphocytes are found in an activated state in the peripheral blood of healthy people and may form part of an immunoregulatory network which actively prevents autoimmunity.

Serum autoantibodies reacting with the hepatic asialoglycoprotein receptor protein (hepatic lectin) in acute and chronic liver disorders

Circulating autoantibodies reacting with affinity-purified, hepatic asialoglycoprotein receptor protein, hepatic lectin (HL), were detected by radioimmunoassay in 15 (83%) of 18 patients with autoimmune chronic active hepatitis (AI-CAH) who had active disease, at titres that showed a positive correlation (P less than 0.05) with severity of periportal inflammation assessed histologically. In contrast, 10 AI-CAH patients whose disease was in remission were all anti-HL seronegative. Anti-HL was also detected in 16 (73%) of 22 patients with hepatitis B virus-related CAH-a similar frequency to that in active AI-CAH but at significantly lower (P less than 0.005) titres. Only 1 of 8 patients with chronic active liver disease due to presumed non-A, non-B (NANB) viral infection and 5 (22%) of 23 with primary biliary cirrhosis were anti-HL seropositive (P less than 0.001 vs active AI-CAH and HBV-CAH) and there was no correlation with severity of periportal inflammation. Anti-HL antibodies were also found in sera from 7 (35%) of 20 patients with acute virus B hepatitis (AVH-B) but were not detected in 10 patients with AVH-A nor in 12 with AVH due to presumed NANB infection. Anti-HL was not found in sera of 12 patients with autoimmune thyroid disease. Hepatic lectin, a highly purifiable, liver-specific cell surface component, by analogy with the acetylcholine and thyrotropin receptors which are, respectively, targets of the pathogenetically-related autoimmune reactions in myasthenia gravis and autoimmune thyroid disease, may be an important target of autoreactions in liver disease.