Type II autoimmune hepatitis. What is the role of the hepatitis C virus?

Molecular mimicry and autoimmune liver disease: virtuous intentions, malign consequences

The pathogenesis of autoimmune liver disease and autoimmunity associated with chronic viral hepatitis remains poorly understood. One of the major hurdles to a deeper understanding of these pathological processes is the absence of clearly defined inductive mechanisms, which, if identified and characterised, could guide clinical strategies for their prevention or allow therapeutic intervention. Molecular mimicry leading to crossreactive autoimmune responses has gained strong experimental support in the past decade. A fundamental premise of this hypothesis is the involvement of a mimicking environmental trigger. In view of the numerous viral and bacterial agents epidemiologically linked to autoimmune liver diseases, we and others have proposed molecular mimicry to be an important mechanism in these diseases. We also propose similar crossreactive mechanisms to operate in the generation of autoimmunity in viral hepatitis. This review focuses on molecular mimicry at the level of the B-cell, as few data on T-cell crossreactivity in liver disease are thus far available.

Virus, liver and autoimmunity

The immune system's ability to distinguish self from nonself is essential for both host defence against microbial antigens and protection of self-antigens from autoimmune destruction. Such discrimination is complicated by extensive structural homology shared between micro-organisms and self-antigens, a condition known as molecular mimicry. Molecular mimicry provides the foundation for an immune response directed against an exogenous agent such as a virus to cross-react with mimicked host self sequences, leading to autoimmunity, and in some cases, tissue injury and autoimmune disease. In this review we analyse studies investigating the role of molecular mimicry and cross-reactive immunity in liver-related autoimmunity.

Overlapping but distinct specificities of anti-liver-kidney microsome antibodies in autoimmune hepatitis type II and hepatitis C revealed by recombinant native CYP2D6 and novel peptide epitopes

Anti-liver-kidney microsome antibodies (anti-LKM) occur in autoimmune hepatitis (AIH) type II and in a subset of patients with hepatitis C. Anti-LKM1 in AIH are directed against cytochrome P4502D6 (CYP2D6), but conflicting data exist concerning the specificity of anti-LKM in hepatitis C. The aim of this study was to evaluate binding specificities of anti-LKM antibodies in both diseases using novel test antigens as well as their inhibitory capacity on CYP2D6 enzyme activity. Sera from 22 patients with AIH type II and 17 patients with hepatitis C being anti-LKM-positive in the immunofluorescence test were investigated for binding to native recombinant CYP2D6 and liver microsomes by ELISA and immunoblotting, and to synthetic peptides covering the region 254-339 (254-273, 257-269, 270-294, 291-310, 307-324, 321-339, 373-389) as well as the novel peptide 196-218 by ELISA. Furthermore, all sera were tested for inhibition of CYP2D6-dependent bufuralol 1'-hydroxylase activity. Twenty of the 22 AIH type II sera (91%) and nine of the 17 hepatitis C sera (53%) were positive for CYP2D6 by ELISA and/or immunoblotting. The previously described major peptide epitope comprising CYP2D6 amino acids 257-269 was recognized by 16 of the 22 AIH sera but by only one hepatitis C serum. A further epitope, 196-218, could be defined for the first time as another immunodominant epitope for AIH because it was recognized by 15 of the 22 AIH (68%) but only three of the 17 hepatitis C sera (18%). With the exception of the peptide 254-273, the other peptides showed no significant reactivity. Analysing the inhibitory properties of anti-LKM antibodies it emerged that 95% of AIH sera and 88% of hepatitis C sera inhibited enzyme function. These data indicate that anti-LKM antibodies in AIH and hepatitis C react with CYP2D6, as shown by their inhibitory activity, and that besides the known epitope 257-269 a further immunodominant epitope exists on CYP2D6 which is recognized by sera from patients with AIH II but hardly by sera from patients with hepatitis C.

Clinical significance of autoantibodies to soluble liver antigen in autoimmune hepatitis

BACKGROUND/AIMS

Classification of autoimmune hepatitis (AIH) into different subgroups according to autoantibody status has been proposed: type I (ANA/SMA), type II (LKM-1) and type III (anti-SLA). However, whether type III AIH forms a clinically distinct disease entity remains controversial. The aim of this study was to evaluate the subclassification of AIH into ANA/SMA and anti-SLA positive patients with regard to clinical, biochemical and histologic differences.

METHODS

Ninety-seven consecutive patients with a well-documented long-term course of AIH with ANA/SMA and/or anti-SLA autoantibodies were studied. Clinical, biochemical and histological features of patients with ANA/SMA and/or anti-SLA autoantibodies were compared in a secondary analysis of data acquired prospectively.

RESULTS

Anti-SLA autoantibodies were found in 21.6% of patients. Anti-SLA-positive patients tended to have lower transaminases (mean: 153 vs. 247 IU/l), gamma-globulins (25 vs. 31%) and bilirubin (1.8 vs. 3.3 mg/dl) in comparison to ANA/SMA positive patients, but there was a large overlap. HLA-type A1 B8 was more frequent in anti-SLA positive patients, while there was no difference in HLA DR3 and DR4 allotype. Response to immunosuppressive therapy was excellent, but relapse occurred frequently. Diagnosis of anti-SLA positive AIH was often delayed (mean: 68 months from first elevation of transaminases) since testing for anti-SLA autoantibodies is currently not generally available.

CONCLUSIONS

ANA/SMA and anti-SLA positive patients share most clinical, biochemical, histologic and prognostic features. Distinction between type I and type III AIH is therefore clinically not helpful. However, testing for anti-SLA autoantibodies helps in the diagnosis of AIH in many patients who may otherwise be misdiagnosed.

A novel assay for detecting antibodies to cytochrome P4502D6, the molecular target of liver kidney microsomal antibody type 1

Liver Kidney Microsomal type 1 (LKM1) antibody, the diagnostic marker of autoimmune hepatitis type 2, is also found in a proportion of patients with hepatitis C virus infection (HCV). It is detected conventionally by the subjective immunofluorescence technique. Our aim was to establish a simple and objective enzyme-linked immunosorbent assay (ELISA) that measures antibodies to cytochrome P4502D6 (CYP2D6), the target of LKM1. An indirect ELISA using eukaryotically expressed CYP2D6 was designed. Absorbance values obtained against a reference microsomal preparation were subtracted from those obtained against a microsomal preparation over-expressing CYP2D6, thus removing the non-CYP2D6-specific reaction. Sera from 51 LKM1 positive patients (21 autoimmune hepatitis and 30 with HCV infection), 111 LKM1 negative patients with chronic liver disease (including 20 with HCV infection) and 43 healthy controls were tested. Of 51 patients positive by immunofluorescence, 48 were also positive by ELISA while all the 154 LKM1 negative subjects were also negative by ELISA. There was a high degree of association between IFL and ELISA as demonstrated by a kappa reliability value of 0.96. The absorbance values by ELISA correlated with immunofluorescence LKM1 titres both in autoimmune hepatitis (r = 0.74, p < 0.001) and HCV infection (r = 0.67, p < 0.001). The simple, objective ELISA described has the potential to replace the standard immunofluorescence technique.

Autoantibody prevalence in children with liver disease due to chronic hepatitis C virus (HCV) infection

HCV infection and interferon-alpha (IFN-alpha) therapy have been associated with autoimmunity. To assess whether chronic liver disease (CLD) due to HCV infection or its treatment with IFN-alpha cause autoimmune manifestations, the prevalence of tissue autoantibodies in 51 children with chronic HCV infection and 84 with other CLD was analysed by standard techniques. Sixty-five percent of patients with chronic HCV infection, 66% with chronic hepatitis B infection and 60% with Wilson's disease were positive for at least one autoantibody. In the 51 subjects with chronic HCV infection (29 treated with IFN-alpha, 22 untreated), tested on 165 occasions over a median of 9 months (range 5-42 months), autoantibodies to nuclei (ANA), smooth muscle (SMA), gastric parietal cell (GPC) and/or liver kidney microsomal type 1 (LKM-1) were similarly prevalent in treated and untreated patients (90% versus 68%, P = 0.12). Positivity for SMA was present in 67%, GPC in 32%, ANA in 10%, LKM-1 in 8% of cases. Treatment with IFN-alpha had to be suspended due to transaminase elevation in one SMA-positive, one ANA-positive but in three of four LKM-1-positive patients. Our results show that: (i) autoantibodies are common in viral-induced hepatitis and Wilson's disease; (ii) positivity for SMA, GPC, ANA is part of the natural course of chronic HCV infection, their prevalence being unaffected by IFN-alpha; and (iii) IFN-alpha should be used cautiously in the treatment of LKM-1/HCV-positive patients.

De-novo autoimmune hepatitis after liver transplantation

BACKGROUND

Late graft dysfunction that does not result from recognised causes, such as rejection, infection, or vascular or biliary complications, can occur after liver transplantation. We investigated a particular type of unexplained graft dysfunction that is associated with autoimmune features in children who underwent transplantation at our unit between 1991 and 1996.

METHODS

Seven (4%) of 180 liver-transplant recipients developed an unexplained but characteristic form of graft dysfunction (five boys, two girls; median age at presentation 10.3 years, range 2.0-19.4). The median period after surgery was 24 months (6-45). The indications for transplantation had been extrahepatic biliary atresia (four patients), Alagille's syndrome (one), drug-induced acute liver failure (one), and alpha1-antitrypsin deficiency (one). Four patients were on triple immunosuppression with cyclosporin, azathioprine, and prednisolone; and three were on tacrolimus. Immunoglobulin measurements, autoantibody studies, serological studies, and HLA typing were undertaken. Liver-biopsy samples were taken.

FINDINGS

Infectious and surgical complications were excluded. Liver-biopsy samples showed the histological changes of chronic hepatitis, including portal and periportal hepatitis with lymphocytes and plasma cells, bridging collapse, and perivenular-cell necrosis without changes typical of acute or chronic rejection. All patients had high concentrations of IgG (median 22 g/L [range 17.2-34.4]) and high titres of autoantibodies. All but one patient responded to prednisolone 2 mg/kg daily and an increase in or addition of azathioprine (1.5 mg/kg daily) within a median of 32 days (7-316). One responder relapsed owing to poor compliance but went into remission after treatment was restored. All six respondents remain in remission on a reduced dose of prednisolone (5-10 mg/day) and 1.5 mg/kg daily azathioprine at a median of 283 days (range 108-730) follow-up.

INTERPRETATION

Our data show that symptoms of autoimmune hepatitis, which are responsive to the classical treatment for this condition, can appear in liver-transplant patients while they are on anti-rejection immunosuppression. Whether the liver damage in these patients is a form of rejection or the consequence of autoimmune attack has yet to be established.

Chronic hepatitis C associated with anti-liver/kidney microsome-1 antibody is not a subgroup of autoimmune hepatitis

To determine whether "autoimmune hepatitis type IIb" should be categorized as a subgroup of autoimmune hepatitis, we conducted a clinicopathological study of 25 adult Japanese patients who were positive for anti-liver/kidney microsome-1 (anti-LKM-1) anti-body and infected with the hepatitis C virus (HCV). Anti-LKM-1 was determined by indirect immunofluorescence and by the double immunodiffusion assays we have developed. Twenty-two patients did not present any unusual symptoms or any associated diseases during the course of their chronic HCV infection. The spectrum of HCV genotypes of these patients did not significantly differ from that of anti-LKM-1-negative Japanese patients with chronic hepatitis C. Histological examination of liver biopsy specimens showed the usual characteristics of chronic hepatitis C and lack of characteristics of autoimmune hepatitis type I. No disease-specific HLA haplotypes were noted, and HLA-DR4, which is detectable in 88.7% of Japanese patients with autoimmune hepatitis type I, was detected in only 50.0% of our group, the same rate as the background frequency. Prednisolone was effective in none of the six patients treated, but interferon was effective in six of ten treated patients (60%). From these results, we conclude that "autoimmune hepatitis type IIb" should not be categorized as autoimmune hepatitis, and that this subgroup is essentially chronic hepatitis C in which an autoantibody has been produced during the course of chronic HCV infection.

Autoimmune hepatitis type 2 and hepatitis C virus infection: study of HLA antigens

BACKGROUND/AIMS

Markers for hepatitis C virus are often detectable in patients suffering chronic hepatitis with liver-kidney microsomal type 1 antibodies. Several authors have suggested that two subsets of those patients can be defined: a) hepatitis C virus negative and b) hepatitis C virus positive. The aim of this work was to further analyze the possible genetic association, HLA class I and II, in these two groups of patients.

METHODS

HLA was analyzed in 49 patients. Class I was studied using a standard lymphocytotoxicity test and in class II a reverse hybridization-based test for DRB1 typing and PCR-SSO for DQB1 typing were used. Sixty healthy Spanish subjects and 39 chronic hepatitis C subjects without anti-LKM1 antibodies were used as control groups for the "a" and "b" subsets, respectively.

RESULTS

No significant association was found with class I specificities in either group. DQB1 typing showed a very significant increase of DQ2 in the "a" group (93.3% vs. 48%; RR = 15; Pc = 0.0025), and DRB1 typing from the "b" group revealed a high association with DR7 (82.3% vs. 43.6%; RR = 6; Pc = 0.0086).

CONCLUSIONS

Our studies revealed a strong association with DQ2 for the "a" group and for the first time an extremely high association with DR7 antigen for the "b" subset. Hence it is possible to establish a different genetic profile in these two patient groups.

Frequency and significance of antibodies to P450IID6 protein in Japanese patients with chronic hepatitis C

BACKGROUND/AIMS

The aims of the current study were to assess the frequency and the significance of antibodies to cytochrome P450IID6 protein (anti-P450IID6) in various diseases among Japanese patients.

METHODS

Sera from 541 patients were tested by indirect immunofluorescence, and the specificity of anti-P450IID6 was ascertained by either enzyme immunoassay (ELISA) or Western blot using recombinant antigen or rat liver microsomes.

RESULTS

Anti-P450IID6 was found in only 6 of 235 patients (2.6%) with chronic active hepatitis (CAH) positive for hepatitis C virus (HCV) antibody and quantitative HCV-RNA with genotypes II and IV. The predominant epitopes on immunoblots were 66 and 50KD, a 10KD band being the newly underfined microsomal antigen. Even in the patients negative for autoantibodies to nuclear antigens (ANA) by routine indirect immunofluorescence test, various ANA were detected by the newly developed recombinant ELISA. These patients were younger, with lower gamma-globulin and IgG levels than patients with autoimmune hepatitis. Three of five patients with anti-P450IID6 responded well to interferon therapy and one received prednisone when interferon was ineffective. Interestingly, only this patient was diagnosed as definite autoimmune hepatitis according to the criteria proposed by the International Autoimmune Hepatitis Group (IAHG). The other five patients who did not satisfy the IAHG criteria might be considered as CAH-C with autoimmune features. No autoimmune hepatitis patients positive for anti-P450IID6 were identified in the current study, indicating that the variant is very rare in Japan.

CONCLUSIONS

Anti-P450IID6 in CAH-C patients in Japan is not as rare as expected. Anti-P450IID6 among Japanese patients has uncertain significance and precludes further characterization of CAH-C with autoimmune features, which might require interferon therapy.

Nonhepatic manifestations and combined diseases in HCV infection

Infection with hepatitis C virus (HCV) may affect not only the liver but also various nonhepatic tissues and organs and may combine with many etiologically unrelated diseases and morbid conditions. Numerous nonhepatic manifestations in HCV infection have been previously reported. For some (eg, cryoglobulinemia), the association is well established. For others, such as sialadenitis and lichen planus, the association is probable (but not completely documented) and, for the remainder, the associations are weak. Extrahepatic manifestations may result from immunological mechanisms as well as virus invasion and replication in the affected extrahepatic tissues and organs. Thyroid abnormalities, primarily Hashimoto's disease, and isolated increases of anti-thyroid antibodies (ATPO) appear to be more frequent in chronic hepatitis C than B or D, with high ATPO titers clustering mainly among females. Interferon-alpha (IFN-alpha) therapy is associated with development of thyroid dysfunction in 5.5-12.9% of patients, usually exposing preexisting subclinical thyroid abnormalities. Mixed cryoglobulinemia (MC) is commonly found (36-45%) in patients with chronic HCV infection; however, only in a minority of cases does it become clinically manifested as systemic vasculitis with purpura, neuropathy, or Raynaud's phenomenon. In a number of patients, MC may terminate in non-Hodgkin's B-cell lymphoma. Treatment of these lymphoproliferative disorders with IFN-alpha is advocated. Idiopathic thrombocytopenia is now recognized more frequently in association with chronic HCV infection and is usually aggravated by IFN-alpha therapy. Patients with porphyria cutanea tarda (PCT) have demonstrated serological markers of HCV infection in 62-82% of cases. The usefulness of IFN-alpha in PCT remains to be demonstrated. Lichen planus has also been found in association with chronic HCV infection, particularly when severe or affecting the oral cavity. Other nonhepatic manifestations have also been reported in HCV infection such as diabetes, corneal ulceration, uveitis, and sialadenitis. These manifestations deserve further study and documentation. Finally, markers of autoimmunity occur with high frequency in chronic HCV infection; however, combination with the classical syndrome of autoimmune hepatitis is rare. In the presence of various autoantibodies, the clinical features of chronic hepatitis C do not appear to be modified and, contrary to general perception, IFN-alpha therapy within randomized controlled trials should not be withheld since the response rate to IFN-alpha does not appear to differ in the presence or absence of low titers of these markers.

Lymphoblastoid interferon alfa treatment in chronic hepatitis C

Interferon is becoming the standard treatment in adults for chronic hepatitis C. Twenty one children with histologically proved chronic hepatitis C (10 boys, range 2.5-13 years), who were otherwise healthy, were enrolled in a randomised controlled study to test their response to interferon alfa. Eleven children were treated with lymphoblastoid interferon alfa (3 million units/m2) for 12 months; 10 children received no treatment. All had raised transaminases and positive antihepatitis C virus (HCV) antibodies and HCV-RNA. Alanine aminotransferase (ALT) serum levels became normal in five (45%) treated patients after a mean of three weeks (range 1-6 weeks) and no relapse had occurred by the end of follow up (30th month). Only one (10%) untreated patient had normal ALT serum levels from the 11th until the 30th month. Disappearance of serum HCV-RNA, persisting throughout the follow up period, was observed in the six children (five treated) whose ALT became normal. Biopsy specimens in treated patients showed a significant improvement in Knodell's score (median (SD) basal 9.0 (2.2); final 2.0 (0.4)). Interferon treatment was well tolerated in all. This study confirms the efficacy of interferon in children with chronic hepatitis C, not only by restoring normal ALT serum levels, but also viral clearance and histological amelioration of liver inflammation. Contrary to reports in adults no biochemical and virological relapses occurred in responder children.

[Autoimmune hepatitis and hepatitis C]

From autoimmune hepatitis (AIH) classification which recognizes three types of AIH, we discuss the main relations between hepatitis C virus (HCV) infection and AIH. Type I AIH is associated with antinuclear and antismooth muscle antibodies, and with other autoimmune diseases. There is no relation between type I AIH and HCV. Type I anti-liver kidney microsome and anti-liver cytosol I antibodies represent the hallmark of type II AIH. Among type II AIH, two subgroups emerged: type IIa AIH (10-40%) are true AIH (sensitive to steroids but worsens with interferon alpha), whereas type IIb AIH (60-90%) appear as a particular form of HCV hepatitis. Type IIb AIH have a moderate activity, a low titer of autoantibodies, anti-GOR antibodies but never anti-liver cytosol I, no sensitivity to steroids but are sensitive to interferon alpha. The hallmark of type III AIH are anti-cytosol antibodies, but these AIH have the same characteristics as type I AIH. The classification between true AIH (I, IIa, III) or "pseudo-AIH" due to HCV infection has major therapeutic implications. Steroids or immunosuppressive treatments are effective in type I, IIa and III AIH but have no efficacy in type IIb AIH. Alpha interferon has an efficacy in type IIb AIH, but it has no efficacy and may even worsen hepatitis in type I, IIa and III AIH.

Recurrent episodes of acute hepatitis associated with LKM-1 (cytochrome P450 2D6) antibodies in identical twin brothers

BACKGROUND/AIMS

Liver/kidney microsomal antibodies have been noted in liver disease of different etiology, e.g. in autoimmune hepatitis, chronic hepatitis C and D virus infection and in drug-induced liver disease. Unlike these, acute hepatitis of unknown etiology associated with high-titer liver/kidney microsomal-1 antibodies (cytochrome P450 2D6) is reported in identical twin brothers.

METHODS

Patients were studied using clinical, biochemical, serological and immunological methods, as well as liver biopsy.

RESULTS

The acute icteric episodes were followed by spontaneous remission with complete normalization of liver function tests and liver histology. During the acute phase, serum titer for liver/kidney microsomal-1 antibodies (detected by indirect immunofluorescence, ELISA and Western blot analysis) was exceedingly high and decreased gradually thereafter. Hepatitis C and D virus infection were excluded by repeated serological testing; exposure to drugs or chemicals was not evident. Concomitant autoimmune disease was not detectable. HLA typing for class 1 and 2 antigens was positive for the HLA haplotype DQ2, but negative for HLA B4, B8, DR3 and DR4.

CONCLUSIONS

The present observations might suggest a hitherto unreported form of acute hepatitis of unknown etiology, distinct from other liver diseases in which liver/kidney microsomal antibodies have been described so far.

Autoimmune hepatitis versus viral hepatitis C

Numerous viruses are capable of inducing the syndrome of chronic hepatitis. Among them are the hepatitis B, C and D viruses. Out of the most common agents of chronic hepatitis, the hepatitis C virus has been found to be strikingly associated with autoimmune diseases and serological markers of autoimmunity. Conversely, the syndrome of genuine autoimmune hepatitis lacks evidence of previous or ongoing virus infection and is diagnosed by additionally excluding metabolic, toxic, and genetic causes of chronic hepatitis, and by the response to immunosuppressive treatment. This review article summarizes the current knowledge of hepatotropic virus-induced autoimmunity. It focuses on the present molecular and immunological definitions, the clinical and molecular distinction between autoimmune hepatitis and chronic viral hepatitis and the implications for the safe and efficacious therapy of these disease entities.

Posttransfusional, LKM-1-autoantibody-positive hepatitis C virus infection, cryoglobulinemia, and aplastic anemia

Aplastic anemia is occasionally caused by viral hepatitis, hepatitis C virus being the most important factor. Pathogenetically, decreased bone marrow function, abnormalities of the bone marrow microenvironment, and immune-mediated suppression of hematopoiesis are important. Hepatitis C virus infection is associated with a variety of extrahepatic manifestations including autoimmune features like cryoglobulinemia, Sjögren's syndrome, and autoimmune hepatitis. Here we report the case of a 42-year-old man with aplastic anemia due to posttransfusional hepatitis C virus infection associated with cryoglobulinemia and LKM-1 autoantibodies. Following a triple immunosuppressive therapy, there was a complete reconstitution of the bone marrow. Serum HCV-RNA as well as plus- and minus-stranded HCV-RNA in peripheral blood mononuclear cells (PBMC) were detected before immunosuppressive therapy. After therapy, serum HCV-RNA persisted. Furthermore, PBMC now were positive for plus-stranded RNA only. However, in bone marrow-derived precursor cells we failed to demonstrate HCV molecules after therapy. This would argue for reconstituted PBMC from newly generated uninfected precursor cells. It remains unclear as to whether the autoimmune character of the disease or the hepatitis C virus infection itself have contributed to the pathogenesis of the aplastic anemia.

Pathology of hepatitis C virus infection

This paper reviews our current knowledge of hepatitis C virus, its structure, epidemiology and pathological effects in man. The histopathological features of acute and chronic hepatitis due to hepatitis C virus are detailed and illustrated. The possible pathogenetic mechanisms involved in the liver injury are outlined and the significance of genotypic subtypes of the virus and of host genetic predisposition in relation to the liver injury and the response to therapy are summarized.

In vitro analysis of metabolic predisposition to drug hypersensitivity reactions

Idiosyncratic hypersensitivity reactions may account for up to 25% of all adverse reactions, and pose a constant problem to physicians because of their unpredictable nature, potentially fatal outcome and resemblance to other disease processes. Current understanding of how drug allergy arises is based largely on the hapten hypothesis: since most drugs are not chemically reactive per se, they must be activated metabolically to reactive species which may become immunogenic through interactions with cellular macromolecules. The role of drug metabolism is thus pivotal to the hapten hypothesis both in activation of the parent compound and detoxification of the reactive species. Although conjugation reactions may occasionally produce potential immunogens (for example, the generation of acylglucuronides from non-steroidal anti-inflammatory drugs such as diclofenac), bioactivation is catalysed most frequently by cytochrome P450 (P450) enzymes. The multifactorial nature of hypersensitivity reactions, particularly the role of often unidentified, reactive drug metabolites in antigen generation, has hampered the routine diagnosis of these disorders by classical immunological methods designed to detect circulating antibodies or sensitized T cells. Similarly, species differences in drug metabolism and immune system regulation have largely precluded the establishment of appropriate animal models with which to examine the immunopathological mechanisms of these toxicities. However, the combined use of in vitro toxicity assays incorporating human tissues and in vivo phenotyping (or, ultimately, in vitro genotyping) methods for drug detoxification pathways may provide the metabolic basis for hypersensitivity reactions to several drugs. This brief review highlights recent efforts to unravel the bases for hypersensitivity reactions to these therapeutic agents (which include anticonvulsants and sulphonamides) using drug metabolism and immunochemical approaches. In particular, examples are provided which illustrate breakthroughs in the identification of the chemical nature of the reactive metabolites which become bound to cellular macromolecules, the enzyme systems responsible for their generation and (possibly) detoxification, and the target proteins implicated in the subsequent immune response.

Autoimmune cholangiopathy: the result of consecutive primary biliary cirrhosis and autoimmune hepatitis?

Autoimmune cholangiopathy is a recently proposed entity that describes a specific group of patients presenting overlapping features of primary biliary cirrhosis and autoimmune hepatitis, i.e., clinical and/or biochemical cholestasis, high titer antinuclear antibody, negative antimitochondrial antibody, and elevated immunoglobulin G. Liver histology shows primary biliary cirrhosis coexisting with varying degrees of parenchymal inflammation. In addition, these patients achieve remission on corticosteroid therapy. The patient in this report fulfilled the above criteria. However, preceding the autoimmune cholangitis stage, a typical antimitochondrial antibody-positive primary biliary cirrhosis was documented with favorable response to ursodeoxycholic acid treatment. Twenty months later, the patient developed autoimmune hepatitis with elevated aspartate aminotransferase and immunoglobulin G and high titer antinuclear antibody as well as corticosteroid dependency, whereas the antimitochondrial antibody disappeared. The patient's sera initially showed reactivity to three mitochondrial proteins, the 74-, 64-, and 56-kilodalton autoantigens of the 2-oxo acid dehydrogenase complexes, which was characteristic of primary biliary cirrhosis. After developing autoimmune hepatitis, reactivity to the 74- and 64-kilodalton antigens disappeared, whereas reactivity to the 56-kilodalton antigen decreased to low levels. Autoimmune cholangitis and probably other forms of the overlap syndrome may result from the association of two diseases: primary biliary cirrhosis and autoimmune hepatitis.

Recognition of uridine diphosphate glucuronosyl transferases by LKM-3 antibodies in chronic hepatitis D

Patients with chronic hepatitis D often have liver-kidney microsomal antibodies type 3 (LKM-3). These antibodies react with several microsomal antigens that have a molecular weight of 55 KDa and an isoelectric point of about 8. We studied the molecular nature of the antigen and, by immunoscreening a human liver cDNA expression library with KM-3 sera, found that uridine diphosphate glucuronosyl transferases (UGT) appeared as candidate antigens. We confirmed the identity of UGT as an antigen by reacting the sera with recombinant rabbit liver UGT proteins. Some sera reacted with rabbit UGT-2 proteins, but UGT-1 proteins were more sensitive and specific in detecting LKM-3 autoantibodies in patient sera. Anti-UGT-1 antibodies were detected in all LKM-3 positive sera from patients with hepatitis D and 1 out of 11 patients with autoimmune hepatitis type 2. Sera from patients who had hepatitis B only did not react with UGT proteins. The UGT proteins are part of the phase II enzymes of drug metabolism and are the first such enzymes to be identified as human autoantigens.

Primary and secondary liver/kidney microsomal autoantibody response following infection with hepatitis C virus

Liver/kidney microsomal autoantibody type 1 (LKM-1), which characterizes a subtype of autoimmune hepatitis, is also found in some patients with chronic hepatitis C virus (HCV) infection. Whether HCV and LKM-1 are accidentally or causally related is unknown. This case report describes a child who became infected by HCV after liver transplantation for end-stage liver disease caused by alpha 1-antitrypsin deficiency. LKM-1 was detected by immunofluorescence, anti-microsomal reactivity by Western blotting, anti-HCV and anti-GOR by immunoenzymatic assays, and HCV RNA by polymerase chain reaction. Two weeks after HCV infection, immunoglobulin (Ig) M LKM-1 appeared, followed by IgG1 LKM-1, with titers increasing to 1/2560; antibodies to a 50-kilodalton liver microsomal protein appeared 2 months later. Sera from day 1 posttransplant became positive for HCV RNA. HCV RNA was also detected in a liver biopsy specimen obtained 3 months after surgery. The patient did not produce anti-HCV and anti-GOR antibodies throughout the study and had no histological evidence of hepatitis. The temporal relationship between HCV infection and LKM-1 production suggests that HCV may trigger a primary autoimmune response. The lack of liver damage attributable to autoimmunity or viral infection may be caused by immunosuppression.