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

HLA-related genetic susceptibility in autoimmune hepatitis according to autoantibody profile

Although the prevalence of autoimmune hepatitis in first-degree relatives is small, the relationship between genetic markers, especially human leucocyte antigens (HLA), and susceptibility to this disease, has been studied for over three decades. The genetic susceptibility to AIH is believed to be different in the two subtypes of the disease, AIH type 1 and AIH type 2. Type 1 AIH has anti-smooth muscle and anti-nuclear antibodies as its main markers, while those of type 2 AIH are the anti-liver/kidney microsome type 1 and anti-liver cytosol type 1 antibodies. The anti-soluble liver antigen/liver-pancreas antibodies, which, in addition to being present in both subtypes, mark an important number of patients without serological markers. Therefore, a third type of disease is questionable. The vast majority of immunogenetic studies compare the differences between the two main types and make no difference between which antibodies are present to define the subtype. This review seeks to analyze what was most important published in the AIH in this context, trying to relate the HLA alleles according to the AIH marker autoantibodies.

Type 2 autoimmune hepatitis: Genetic susceptibility

Two types of autoimmune hepatitis (AIH) are recognized; AIH-1 is characterized by the presence of anti-nuclear and/or anti-smooth muscle autoantibodies, while AIH-2 is associated with the presence of anti-Liver kidney microsome and/or anti-Liver Cytosol antibodies. The autoantigens targeted by AIH-2 autoantibodies are the cytochrome P450 2D6 and Formiminotransferase-cyclodeaminase for anti-LKM1 and anti-LC1 respectively. Both autoantigens are expressed in hepatocytes at higher levels than in any other cell type. Therefore, compared to AIH-1, the autoantigens targeted in AIH-2 are predominantly tissue-specific. Distinct clinical features are specific to AIH-2 compared to AIH-1, including diagnosis in younger patients (mean age 6.6 years), onset as fulminant hepatitis in very young patients (3 years of age or less), higher frequency in children than in adults and is frequently associated with extrahepatic T cell-mediated autoimmune diseases. AIH-2 is also often diagnosed in patients with primary immunodeficiency. AIH-2 is associated with specific HLA class II susceptibility alleles; DQB1*0201 is considered the main determinant of susceptibility while DRB1*07/DRB1*03 is associated with the type of autoantibody present. HLA DQB1*0201 is in strong linkage disequilibrium with both HLA DRB1*03 and DRB1*07. Interestingly, as in humans, MHC and non-MHC genes strongly influence the development of the disease in an animal model of AIH-2. Altogether, these findings suggest that AIH-2 incidence is likely dependent on specific genetic susceptibility factors combined with distinct environmental triggers.

Precision medicine for autoimmune hepatitis

Autoimmune hepatitis (AIH) is an autoimmune liver disease induced by environmental factors in genetically susceptible individuals. AIH is characterized by hypergammaglobulinemia, elevation of serum autoantibodies and transaminases, and interface hepatitis. Personalized therapy is necessary in AIH because of its heterogeneity in clinical manifestations. Precision medicine is a recent and novel therapeutic pattern which ultimately aims to achieve personalized therapy. In this review we summarize the research progress of precision medicine to treat AIH by an exploration of the susceptible genes, precision diagnosis and prognosis of AIH, pharmacogenomics and precision medication, and the precision treatment for special types of AIH.

Diagnostic approach to autoimmune hepatitis

INTRODUCTION

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease which, if left without treatment, can evolve into cirrhosis and possibly liver failure. The diagnosis of AIH is hampered by the lack of specific and reliable markers of the disease and a number of clinical, biochemical, immunological, histological and genetic factors should be considered to reach a confident diagnosis Areas covered: Clinical expression of AIH, histological features, serological and genetic profiles, differential diagnosis, overlap with other autoimmune liver diseases, assessed on the basis of personal experience and review of published literature in the last 10 years through a systematic Medline search (keywords: autoimmune hepatitis, diagnosis) Expert commentary: Notwithstanding numerous efforts to identify simple and reliable markers of the disease, the diagnosis of AIH is still based on the combination of histological, immunological and biochemical features and often can represent a real challenge for the hepatologist.

Autoantibody presentation in drug-induced liver injury and idiopathic autoimmune hepatitis: the influence of human leucocyte antigen alleles

OBJECTIVES

Positive autoantibody (AAB) titres are commonly encountered in autoimmune hepatitis (AIH) and in a proportion of drug-induced liver injury (DILI) patients. The underlying mechanism for selective AAB occurrence in DILI is unknown, but could be associated with variations in immune-associated genes. Hence, we aimed to analyse human leucocyte antigen (HLA) allele compositions in DILI with positive (+) and negative (-) AAB titres and in AIH patients.

METHODS

High-resolution genotyping of HLA class I (A, B, C) and II (DRB1, DQB1) loci was performed on 207 DILI and 50 idiopathic AIH patients and compared with 885 healthy Spanish controls.

RESULTS

Compared with controls, HLA-B*08:01 [44 vs. 9.7%, P=3.7E-13/corrected P-value (Pc)=1.0E-11], C*07:01 (46 vs. 24%, P=6.4E-04/Pc=0.012), DRB1*03:01 (58 vs. 21.5%, P=5.0E-09/Pc=1.0E-07) and DQB1*02:01 (56 vs. 22%, P=6.8E-08/Pc=9.0E-07) were significantly more frequent in AIH patients. The HLA-A*01:01 frequency was increased in the same population, but did not reach significance after Bonferroni's correction (34 vs. 19%, P=0.02/Pc=0.37). Fifty-eight of 207 DILI patients presented positive titres for at least one AAB (predominantly antinuclear antibody 76% and antismooth muscle antibody 28%). There was a tendency towards higher representation of DRB1*14:01 and DQB1*05:03 in DILI AAB+ compared with DILI AAB- (13.8 vs. 4.0%, P=0.02/Pc=0.5; 13.8 vs. 4.7%, P=0.04/Pc=0.5).

CONCLUSION

The presence of HLA alleles B*08:01, C*07:01, DRB1*03:01, DQB1*02:01 and possibly A*01:01 enhances the risk of AIH (type 1) in Spanish patients. These alleles form part of the ancestral haplotype 8.1. HLA-DRB1*14:01 and DQB1*05:03 could potentially increase the risk of positive AAB (particularly antinuclear antibody) in Spanish DILI patients.

Transitioning from Idiopathic to Explainable Autoimmune Hepatitis

Autoimmune hepatitis lacks an identifiable cause, and its diagnosis requires the exclusion of etiologically defined diseases that resemble it. Insights into its pathogenesis are moving autoimmune hepatitis from an idiopathic to explainable disease, and the goal of this review is to describe the insights that are hastening this transition. Two types of autoimmune hepatitis are justified by serological markers, but they also have distinctive genetic associations (DRB1 and DQB1 genes) and autoantigens. DRB1 alleles are the principal susceptibility factors in white adults, and a six amino acid sequence encoded in the antigen-binding groove of class II molecules of the major histocompatibility complex can influence the selection of autoantigens. Polymorphisms, including variants of SH2B3 and CARD10 genes, may affect immune reactivity and disease severity. The cytochrome mono-oxygenase, CYP2D6, is the autoantigen associated with type 2 autoimmune hepatitis, and it shares homologies with multiple viruses that might promote self-intolerance by molecular mimicry. Chemokines, especially CXCL9 and CXCL10, orchestrate the migration of effector cells to sites of injury and are associated with disease severity. Cells of the innate and adaptive immune responses promote tissue damage, and possible deficiencies in the number and function of regulatory T cells may facilitate the injurious process. Receptor-mediated apoptosis is the principal mechanism of hepatocyte loss, and cell-mediated and antibody-dependent mechanisms of cytotoxicity also contribute. Insights that explain autoimmune hepatitis will allow triggering exogenous antigens to be characterized, risk management to be improved, prognostic indices to be refined, and site-specific therapeutic interventions to emerge.

Clinical features and effect of antiviral therapy on anti-liver/kidney microsomal antibody type 1 positive chronic hepatitis C

BACKGROUND/AIMS

Anti-liver/kidney microsomal antibody type 1 (anti-LKM1), a serological marker of type 2 autoimmune hepatitis, is also detected in a small proportion of patients with hepatitis C. This study aimed to evaluate clinical features and effect of antiviral therapy in patients with hepatitis C who are anti-LKM1 positive.

METHODS

Sixty consecutive anti-LKM1 positive and 120 age and sex-matched anti-LKM1 negative chronic hepatitis C patients were assessed at diagnosis and during follow-up. Of these, 26 anti-LKM1 positive and 72 anti-LKM1 negative received antiviral therapy. Anti-LKM1 was detected by indirect immunofluorescence and immunoblot. Number of HCV-infected hepatocytes and intrahepatic CD8+ lymphocytes was determined by immunohistochemistry.

RESULTS

At diagnosis anti-LKM1 positive patients had higher IgG levels and more intrahepatic CD8+ lymphocytes (p 0.022 and 0.046, respectively). Viral genotypes distribution and response to therapy were identical. Hepatic flares during antiviral treatment only occurred in a minority of patients in concomitance with anti-LKM1 positivity.

CONCLUSIONS

Immune system activation is more pronounced in anti-LKM1 positive patients with hepatitis C, possibly representing the expression of autoimmune mechanisms of liver damage. Antiviral treatment is as beneficial in these patients as in anti-LKM1 negative patients, and the rare necroinflammatory flares are effectively controlled by corticosteroids, allowing subsequent resumption of antiviral therapy.

Influence of genes, sex, age and environment on the onset of autoimmune hepatitis

The pathogenesis of autoimmune hepatitis (AIH) is complex. However, it is believed that a susceptible individual, owing to his genetic background, sex and age, can develop the disease following exposure to an environmental trigger. Autoimmune hepatitis does not follow a Mendelian pattern of inheritance; hence no single causative genetic locus has been identified. However, several genes, inside and outside the HLA locus, have been linked to an increased susceptibility to AIH. Epidemiological evidence also suggests that the sex and age of the patient plays a role in AIH pathogenesis as the disease onset occurs mainly in the two first decades of life and a higher disease incidence is observed in females. No environmental trigger has been identified, but several have been proposed, mainly viruses and xenobiotics. This article aims at reviewing the current knowledge on susceptibility factors leading to AIH and putative triggers, emphasizing fundamental mechanisms responsible for the break of liver immunological tolerance.

HLA and autoimmune digestive disease: a clinically oriented review for gastroenterologists

OBJECTIVES

The human leukocyte antigen (HLA) system includes genes involved in graft-vs-host rejection and in immune response. The discovery that HLAs are associated with several diseases led to appealing developments both in basic biomedical research and in clinical medicine, and offered the opportunity to improve the understanding of pathogenesis and classification of diseases, as well as to provide diagnostic and prognostic indicators. The aim of this article is to review the association between HLA alleles and autoimmune digestive disease and its current relationship with modern HLA nomenclature and clinical practice.

METHODS

Articles dealing with the association between HLAs and autoimmune digestive disease (including celiac disease, inflammatory bowel disease, autoimmune hepatitis, sclerosing cholangitis and primary biliary cirrhosis) were searched for using Pubmed and SCOPUS databases from earliest records to January 2008.

RESULTS

The review has provided two sections. In the first, we explain the basic principles of HLA structure, function, and nomenclature, as an introduction to the second section, which describes current associations between HLA alleles and digestive diseases. The clinical implications of each HLA association are critically discussed. Actually, a clinical role for HLA typing is suggested for only a few conditions, e.g., celiac disease.

CONCLUSIONS

The knowledge of current HLA nomenclature and of its association with some digestive diseases such as celiac disease can be useful in clinical practice for diagnostic and prognostic purposes. This can avoid improper HLA typing as well as stressing the need for further studies on other possible clinical applications.

Genetic factors affecting the occurrence, clinical phenotype, and outcome of autoimmune hepatitis

Autoimmune hepatitis is a polygenic disorder of unknown cause in which the genetic risk factors that affect occurrence, clinical phenotype, severity, and outcome still are being clarified. The susceptibility alleles in white North American and northern European patients reside on the DRB1 gene, and they are DRB1*0301 and DRB1*0401. These alleles encode a 6 amino acid sequence at positions 67-72 in the DRbeta polypeptide chain of the class II molecules of the major histocompatibility complex. This sequence is associated with susceptibility, and lysine at position DRbeta71 is the key determinant. Molecular mimicry between foreign and self-antigens may explain the loss of self-tolerance and the occurrence of concurrent immune diseases in anatomically distant organs. Disease severity is associated with the number of alleles encoding lysine at DRbeta71 (gene dose) and the number of polymorphisms, including those of the tumor necrosis factor-alpha gene, cytotoxic T lymphocyte antigen-4 gene, and tumor necrosis factor-receptor superfamily gene, that can modify the immune response. Individuals in different geographic regions may have different susceptibility alleles that reflect indigenous triggering antigens, and these may provide clues to the etiologic agent. Knowledge of the genetic predispositions for autoimmune hepatitis may elucidate pathogenic mechanisms, identify etiologic agents, characterize susceptible populations, foresee outcomes, and target new therapies. These lessons may be applicable to autoimmune disease in general.

Autoimmune hepatitis. Part A: pathogenesis

Autoimmune hepatitis is a consequence of a triggering antigen and genetic factors that favor the presentation of autoantigens, polymorphisms that affect immunocyte activation and durability, cytokine alterations that promote proliferation of liver-infiltrating cytotoxic T cells, and perturbations in the number and function of immune-regulatory cell populations, including T regulatory cells and natural killer T cells. The triggering epitope is probably a short sequence peptide that is common in multiple infectious or toxic agents. Homologies between this epitope and self-antigens (molecular mimicry) may stimulate humoral and cellular responses that are cross-reactive. Sensitized immunocytes extend and perpetuate the inflammation through imprecise targeting of self-antigens that resemble foreign antigens (promiscuous behavior). The occurrence and clinical phenotype of the disease may relate to genetic susceptibility factors that favor protracted exposure to indigenous etiological agents, and these genetic factors can vary in different geographical regions and ethnic groups. The clinical phenotype within a population can be modified further by genetic polymorphisms that are not disease specific and that affect immunocyte activation, differentiation, proliferation and programmed death (apoptosis). Autoimmune hepatitis is a model of autoreactivity that reflects multiple disturbances in the counter-regulatory mechanisms essential for immune homeostasis.

Evidence of a genetic basis for the different geographic occurrences of liver/kidney microsomal antibody type 1 in hepatitis C

Antibodies to liver/kidney microsome type 1 occur in Italian patients with hepatitis C, but rarely develop in North American patients. Our goals were to compare the frequencies of the HLA markers associated with autoimmune expression in Italian and North American patients with chronic hepatitis C and to determine genetic bases for regional differences in antibody production. HLA B8, DR3, DR4, DR7, DR11, DR13, DQ2, and the B8-DR3-DQ2 haplotype were determined by microlymphocytotoxicity and polymerase chain reaction in 105 Italian patients (50 with microsomal antibodies), 100 North American patients (none with microsomal antibodies), and Italian and North American healthy control subjects. Italian patients with microsomal antibodies differed from North American patients without these antibodies by having a higher frequency of HLA DR7 (54% vs. 27%, P=0.002). HLA DR7 occurred more frequently in seropositive Italian patients than in seronegative counterparts (54% vs. 11% P < 0.0001), Italian healthy control subjects (54% vs. 29%, P=0.0009), and North American healthy control subjects (54% vs. 19%, P < 0.0001). The frequency of HLA DR7 was similar in North American patients and controls (27% vs. 19%, P=0.2), but it was lower than in Italian controls (19% vs. 29%, P=0.059). Seropositive Italian patients had a lower frequency of HLA DR11 than seronegative Italian patients and Italian controls (18% vs. 34%, P=0.07, and 18% vs. 35%, P=0.02, respectively). In contrast to seropositive Italian patients, North American patients had HLA DR4 (30% vs. 12%, P=0.02), HLA DR13 (29% vs. 10%, P=0.01), and the B8-DR3-DQ2 haplotype (23% vs. 6%, P=0.01) more often. Similarly, HLA DR4 and the B8-DR3-DQ2 phenotype were more frequent in North American patients than in Italian controls (30% vs. 16%, P=0.005, and 23% vs. 7%, P=0.00002, respectively). HLA DR7 is associated with the development of microsomal antibodies in Italian patients with chronic hepatitis C. The lower frequency of HLA DR7 in North America could contribute to the rarity of these antibodies in this region. HLA DR11 may be protective against the development of microsomal antibodies in Italian patients, whereas HLA DR4, HLA DR13, and the B8-DR3-DQ2 haplotype may be protective in North American patients.

HLA class II influences humoral autoimmunity in patients with type 2 autoimmune hepatitis

BACKGROUND/AIMS

Type 2 autoimmune hepatitis (AIH) is characterized by the presence of anti-liver kidney microsome (anti-LKM-1) and/or anti-liver cytosol type 1 (anti-LC1) autoantibodies. However, the correlation between these autoantibodies and the genetic background has not been studied.

METHODS

Frequencies of HLA class II alleles were compared between the 60 Caucasian children with type 2 AIH and 313 control subjects. The anti-LKM1 antibody reactivity directed against antigenic sites of CYP2D6 was analysed by ELISA.

RESULTS

HLA-DQB1 *0201 allele was found to be the primary genetic determinant of susceptibility to type 2 AIH by conferring the highest odd-ratio (OR = 6.4). HLA-DRB1 *03 allele was significantly increased (P < 0.0001) among patients with both anti-LKM1 and anti-LC1 autoantibodies as well as in those with only anti-LC1(+) compared to those with anti-LKM1(+) alone. In contrast, HLA-DRB1 *07 allele was significantly associated (P < 0.0001) with anti-LKM1(+) alone compared to groups with both anti-LKM and anti-LC1 or with LC1+ alone. Children with the DRB1 *07 allele develop anti-LKM1 autoantibodies having a more restricted specificity (2 epitopes) than to those having HLA-DRB1 *03 allele (5 epitopes).

CONCLUSIONS

The HLA-DR locus is involved in autoantibody expression, while the DQ locus appears to be a critical determinant for the development of type 2 AIH.

Genetic distinctions between autoimmune hepatitis in Italy and North America

AIM: Our goals were to analyze the known genetic predispositions for autoimmune hepatitis (AIH) in AIH Italian population and to compare them with North American counterparts.

METHODS: Human leukocyte antigens (HLA) B8, C7, DR3, DR4, DR7, DR11, DR13, DQ2 and the B8-DR3-DQ2 phenotype were determined by microlymphocytotoxicity and polymerase chain reaction in 74 Italian patients (57 with type 1 and 17 with type 2 AIH) and 149 North American patients with type 1 AIH, and in adequate controls.

RESULTS: B8-DR3-DQ2 occurred more frequently in Italian patients with type 1 AIH than in Italian controls (30% vs 7%, P<0.0001), but less frequently than in North American counterparts (30% vs 48%, P = 0.02). DR4 occurred less frequently in Italian patients with type 1 AIH (23% vs 43%, P = 0.01) and in controls (16% vs 34%, P = 0.0003) than in North American counterparts. No differences were found in alleles’ frequency between type 1 and type 2 Italian AIH patients. DR11 had a frequency lower in type 1 Italian AIH patients than controls (17% vs 35%, P = 0.01).

CONCLUSION: HLA DR4 is not associated with AIH in Italy. The known HLA risk factors for AIH occur similarly in Italian patients with type 1 and type 2 AIH, and they are less frequent than in North American patients. B8-DR3-DQ2 is the predominant phenotype of type 1 AIH also in Italy, and HLA DR11 may be a regionally distinctive protective factor against type 1 AIH.

Host genetic determinants in hepatitis C virus infection

In addition to viral and environmental/behavioural factors, host genetic diversity is believed to contribute to the spectrum of clinical outcomes in hepatitis C virus (HCV) infection. This paper reviews the literature with respect to studies of host genetic determinants of HCV outcome and attempts to highlight trends and synthesise findings. With respect to the susceptibility to HCV infection, several studies have replicated associations of the HLA class II alleles DQB1(*)0301 and DRB1(*)11 with self-limiting infection predominantly in Caucasian populations. Meta-analyses yielded summary estimates of 3.0 (95% CI: 1.8-4.8) and 2.5 (95% CI: 1.7-3.7) for the effects of DQB1(*)0301 and DRB1(*)11 on self-limiting HCV, respectively. Studies of genetics and the response to interferon-based therapies have largely concerned single-nucleotide polymorphisms and have been inconsistent. Regarding studies of genetics and the progression of HCV-related disease, there is a trend with DRB1(*)11 alleles and less severe disease. Studies of extrahepatic manifestations of chronic HCV have shown an association between DQB1(*)11 and DR3 with the formation of cryoglobulins. Some important initial observations have been made with respect to genetic determinants of HCV outcome. Replication studies are needed for many of these associations, as well as biological data on the function of many of these polymorphisms.

Multiple viral/self immunological cross-reactivity in liver kidney microsomal antibody positive hepatitis C virus infected patients is associated with the possession of HLA B51

Liver Kidney Microsomal autoantibody type 1(LKM1) directed to cytochrome P4502D6 (CYP2D6) characterises autoimmune hepatitis type-2 (AIH-2), but is also found in a proportion of chronic hepatitis C virus (HCV) infected patients, CYP2D6252-271 being a major B- cell autoepitope. Molecular mimicry and immunological cross-reactivity between CYP2D6252-271, HCV polyprotein and the infected cell protein 4 (ICP4) of herpes simplex virus type 1 (HSV-1) have been suggested as triggers for the induction of LKM1, but reactivity and cross-reactivity to the relevant sequences have not been investigated experimentally. CYP2D6252-271 and its viral homologues were constructed and tested by ELISA in the sera of 46 chronically infected HCV patients, 23 of whom were LKM1 positive. Reactivity to the E1 HCV and ICP4 HSV1 mimics was frequently found in HCV infected patients irrespectively of their LKM1 status; viral/self cross-reactivity (as indicated by inhibition studies), however, was present in the only 2 of the 23 LKM1 seropositive HCV patients, who possessed the HLA allotype B51. Our results indicate that in HCV infected patients virus/self cross-reactivity is dependent on a specific immunogenetic background, a finding awaiting confirmation by studies in larger series of patients.

Autoantibodies and autoantigens in autoimmune hepatitis: important tools in clinical practice and to study pathogenesis of the disease

Autoimmune hepatitis (AIH) is a chronic necroinflammatory disease of the liver characterized by hypergammaglobulinemia, characteristic autoantibodies, association with HLA DR3 or DR4 and a favorable response to immunosuppressive treatment. The etiology is unknown. The detection of non-organ and liver-related autoantibodies remains the hallmark for the diagnosis of the disease in the absence of viral, metabolic, genetic, and toxic etiology of chronic hepatitis or hepatic injury. The current classification of AIH and the several autoantibodies/target-autoantigens found in this disease are reported. Current aspects on the significance of these markers in the differential diagnosis and the study of pathogenesis of AIH are also stated. AIH is subdivided into two major types; AIH type 1 (AIH-1) and type 2 (AIH-2). AIH-1 is characterized by the detection of smooth muscle autoantibodies (SMA) and/or antinuclear antibodies (ANA). Determination of antineutrophil cytoplasmic autoantibodies (ANCA), antibodies against the asialoglycoprotein receptor (anti-ASGP-R) and antibodies against to soluble liver antigens or liver-pancreas (anti-SLA/LP) may be useful for the identification of patients who are seronegative for ANA/SMA. AIH-2 is characterized by the presence of specific autoantibodies against liver and kidney microsomal antigens (anti-LKM type 1 or infrequently anti-LKM type 3) and/or autoantibodies against liver cytosol 1 antigen (anti-LC1). Anti-LKM-1 and anti-LKM-3 autoantibodies are also detected in some patients with chronic hepatitis C (HCV) and chronic hepatitis D (HDV). Cytochrome P450 2D6 (CYP2D6) has been documented as the major target-autoantigen of anti-LKM-1 autoantibodies in both AIH-2 and HCV infection. Recent convincing data demonstrated the expression of CYP2D6 on the surface of hepatocytes suggesting a pathogenetic role of anti-LKM-1 autoantibodies for the liver damage. Family 1 of UDP-glycuronosyltransferases has been identified as the target-autoantigen of anti-LKM-3. For these reasons the distinction between AIH and chronic viral hepatitis (especially of HCV) is of particular importance. Recently, the molecular target of anti-SLA/LP and anti-LC1 autoantibodies were identified as a 50 kDa UGA-suppressor tRNA-associated protein and a liver specific enzyme, the formiminotransferase cyclodeaminase, respectively. Anti-ASGP-R and anti-LC1 autoantibodies appear to correlate closely with disease severity and response to treatment suggesting a pathogenetic role of these autoantibodies for the hepatocellular injury. In general however, autoantibodies should not be used to monitor treatment, predict AIH activity or outcome. Finally, the current aspects on a specific form of AIH that may develop in some patients with a rare genetic syndrome, the autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome (APECED) are also given. Autoantibodies against liver microsomes (anti-LM) are the specific autoantibodies detected in AIH as a disease component of APECED but also in cases of dihydralazine-induced hepatitis. Cytochrome P450 1A2 has been identified as the target-autoantigen of anti-LM autoantibodies in both APECED-related AIH and dihydralazine-induced hepatitis. The latter may indicate that similar autoimmune pathogenetic mechanisms can lead to liver injury in susceptible individuals irrespective of the primary defect. Characterization of the autoantigen-autoantibody repertoire continues to be an attractive and important tool to get access to the correct diagnosis and to gain insight into the as yet unresolved mystery of how hepatic tolerance is given up and AIH ensues.

Non-organ-specific autoantibodies in children with chronic hepatitis C: clinical significance and impact on interferon treatment

We evaluated the prevalence and clinical significance of non-organ-specific autoantibodies (NOSAs) in 47 hepatitis C virus (HCV)-positive children with abnormal alanine transaminase levels and analyzed the association between NOSAs and virus level, genotype, human leukocyte antigen status, and interferon (IFN) response. Forty-two hepatitis B virus (HBV)-positive children and 25 age- and sex-matched healthy children served as control subjects. NOSAs were found in 34% of the HCV-positive children, 12% of the HBV-positive controls, and none of the healthy control subjects. Liver-kidney microsomal antibody type 1 (LKM1) was detected in 11% of the HCV-positive children but in none of the controls. The HCV load was significantly higher in NOSA-negative than in NOSA-positive children. HCV genotype distribution and human leukocyte antigen alleles were similar, irrespective of NOSA status. Long-term response to IFN therapy was achieved by 18% of the NOSA-positive and 55% of the NOSA-negative subjects. Two LKM1-positive children developed acute, self-limited hepatocellular necrosis while receiving IFN therapy. NOSAs are frequently present in children with hepatitis C, who are less likely to benefit from IFN therapy.

Hepatitis C virus infection associated with liver-kidney microsomal antibody type 1 (LKM1) autoantibodies in children

OBJECTIVE

To evaluate the clinical pattern and evolution of chronic hepatitis C in children with liver/kidney microsomal antibody type 1 autoantibodies (LKM1).

STUDY DESIGN

A multicenter, retrospective study, including the following groups of children with hepatitis C virus infection: (1). 21 consecutive LKM1-positive patients, (2). 42 age- and sex- matched LKM1-negative patients, and (3). 4 interferon-induced LKM1-positive cases. LKM1 reactivity to human microsomes and recombinant cytochrome P450IID6 (CYP2D6) was assayed by immunoblotting.

RESULTS

Clinical and biochemical features overlapped in LKM1-positive and LKM1-negative children, but a fibrosis score >3 (range 0-6) was significantly more frequent (P =.04) in the former. Reactivity to microsomal protein and CYP2D6 was significantly (P =.02) associated with LKM1 titers >or=1:320 and was found in 39% of patients, including severe cases and both children (of 4 treated) who achieved a sustained alanine aminotransferase (ALT) normalization after steroid treatment. Five of 7 LKM1-positive children treated with interferon had an ALT exacerbation.

CONCLUSIONS

LKM1-positive hepatitis C in children is characterized by a wide spectrum of biochemical, serologic, and histologic features. Whether autoimmunity may contribute to liver damage in a subgroup of patients with more severe liver disease, high LKM1 titers, and reactivity to CYP2D6 is a question deserving further investigation.

Autoantibodies and defined target autoantigens in autoimmune hepatitis: an overview

Autoimmune hepatitis (AIH) is a disease of unknown aetiology characterised by hypergammaglobulinaemia, non-organ and liver-related autoantibodies, association with HLA-DR3 or DR4 and a favourable response to immunosuppression. The current classification of AIH and the several autoantibodies/target autoantigens found in this disease are reported. The importance of these markers in the differential diagnosis and the study of pathogenesis of AIH is also given. AIH is subdivided into two major types: AIH type 1 (AIH-1) and AIH type 2 (AIH-2). AIH-1 is characterised by the detection of smooth muscle autoantibodies (SMA) and/or antinuclear antibodies (ANA). Antineutrophil cytoplasmic autoantibodies (ANCA), in most cases of perinuclear pattern (p-ANCA), by the indirect immunofluorescence assay, antibodies against the asialoglycoprotein receptor (anti-ASGP-R) and antibodies to soluble liver antigens or liver-pancreas (anti-SLA/LP) may be useful for the identification of individuals who are seronegative for ANA/SMA. AIH-2 is characterised by the presence of specific autoantibodies against liver and kidney microsomal antigens (anti-LKM type 1 or infrequently anti-LKM type 3) and/or autoantibodies against liver cytosol 1 antigen (anti-LC1). Anti-LKM-1 and anti-LKM-3 autoantibodies are also detected in some patients with chronic hepatitis C (HCV) and chronic hepatitis D (HDV). For these reasons, the distinction between AIH and chronic viral hepatitis is of particular importance. Cytochrome P450 2D6 (CYP2D6) is the major target autoantigen of anti-LKM-1 autoantibodies in both conditions (AIH-2 and HCV infection). Recent data have demonstrated the expression of CYP2D6 on the surface of hepatocytes, suggesting a pathogenetic role of anti-LKM-1 autoantibodies in liver injury. Family 1 of UDP-glycuronosyltransferases has been identified as the target autoantigen of anti-LKM-3. The molecular target of anti-SLA/LP autoantibodies has been identified recently as a 50 kDa protein with unknown structure and function. A liver-specific enzyme, the formiminotransferase cyclodeaminase, was identified as the target autoantigen of anti-LC1 autoantibodies. Anti-ASGP-R and anti-LC1 autoantibodies appear to correlate better with the severity of AIH and the response to treatment. The latter may suggest a pathogenic role of these autoantibodies in the hepatocellular damage in AIH. In general, however, autoantibodies should not be used to monitor treatment or to predict AIH activity or outcome. Finally, current knowledge concerning a specific form of AIH that may develop in some patients with a rare genetic syndrome, the autoimmune polyglandular syndrome type-1 (APS-1), is also discussed. Autoantibodies against liver microsomes (anti-LM) are the specific autoantibodies found in AIH as a disease component of APS-1. However, anti-LM autoantibodies have also been described in cases of dihydralazine-induced hepatitis. Cytochrome P450 1A2 has been identified as the target autoantigen of anti-LM autoantibodies in both disease entities.

Relationship between autoimmune hepatitis and HLA-DR4 and DRβ allelic sequences in the third hypervariable region in Chinese

AIM: To analyze the association of HLA-DRB1 with autoimmune hepatitis (AIH) in patients from China.

METHODS: In 32 patients and 48 healthy controls, polymerase chain reaction amplification with sequence-specific primers (PCR-SSP) was performed to examine the association of certain alleles or polymorphic sequences of HLA-DRB1 with AIH.

RESULTS: HLA-DRB1 typing by PCR-SSP showed that DR4 had a significantly increased frequency among patients with AIH versus healthy control (46.9% versus 20.8%; relative risk = 3.35, P = 0.014). In subtypes of DR4, there was a trend of increase in the gene frequency of DRB1 *0405 in patients with AIH versus healthy controls (21.9% vs 6.3%, P = 0.04, but P_c = 0.08). In addition, a significant increase was found in the alleles frequency encoding QRRAA from the third hyperpolymorphic region of DR4 in the patients with AIH (86.7% of DR4 positive patients vs 40.0% in DR4 positive controls, P = 0.016, P_c = 0.028, RR = 9.75).

CONCLUSION: AIH in Chinese is associated with HLA-DR4. There is a relationship between QRRAA sequence within the third hyperpolymorphic region of the DRB allele and AIH in Chinese.

Autoimmune hepatitis in Brazilian patients is not linked to tumor necrosis factor alpha polymorphisms at position -308

BACKGROUND/AIMS

Susceptibility to autoimmune hepatitis (AIH) has been linked to different HLA-DR antigens. Recently, AIH type 1 was associated with polymorphisms in the tumor necrosis factor alpha gene promoter (TNFA) at position -308. In this respect, the frequency of the TNFA*2 allele, in linkage disequilibrium with HLA-DRB1*0301, was shown to be significantly increased in whites with AIH type 1. The aim of this study was to assess the role of TNFA alleles in conferring susceptibility to AIH, studying a population where the disease is not primarily associated with HLA-DRB1*03.

METHODS

The determination of HLA-DRB1 and TNFA alleles was performed in 92 patients with AIH type 1, 29 subjects with AIH type 2 and 83 healthy controls by polymerase chain reaction-based techniques.

RESULTS

The distribution of TNFA alleles was similar in patients with AIH types 1 and 2, when compared with controls. In addition, the TNFA*2 allele was identified in patients carrying HLA-DR antigens other than HLA-DRB1*03. Interestingly, higher gammaglobulin levels were observed in TNFA*2 positive patients.

CONCLUSIONS

Our data indicate that susceptibility to AIH remains primarily linked to the HLA-DRB1 locus, and suggest that the association of AIH with TNFA*2 previously observed in whites might be secondary to a linkage disequilibrium with HLA-DRB1*0301.

Autoimmune hepatitis

Autoimmune hepatitis (AIH) is a rare disease, characterized by female predominance, hypergammaglobulinemia, autoantibodies, association with HLA DR3 and HLA DR4 and a good response to immunosuppression. Different subtypes of AIH may be distinguished, based on differences in the autoantibody patterns. AIH type 1 is characterized by anti-nuclear (ANA) and/or anti-smooth muscular (SMA) autoantibodies. AIH type 2 is characterized by liver/kidney microsomal autoantibodies (LKM). AIH type 3 may be distinguished by autoantibodies to soluble liver proteins (SLA) or the liver pancreas antigen (LP). AIH-2 affects predominantly pediatric patients and is characterized by a more severe clinical course, a higher frequency of relapse under immunosuppressive treatment and a more frequent progression to cirrhosis. In contrast, AIH types 1 and 3 show a higher age of onset and a better long-term response to immunosuppressive treatment. At present, the treatment of choice is prednisone alone or a combination with prednisone and azathioprine. Both treatment protocols show high survival rates. However, a rate of 13% of treatment failures and the failure to induce permanent remission in most patients underlines the urgent need to develop additional treatment regimens. A yet unknown genetic predisposition is believed to act as the underlying etiological factor in AIH. This genetic predisposition includes a few known risk factors such as the presence of HLA DR3 or HLA DR4, deletions of C4A alleles and female gender. Furthermore, it has to be postulated that defects in immunoregulatory genes exist. A model for such defects may be the autoimmune polyglandular syndrome type 1 (APS1), which results from the defects in a single gene, the autoimmune regulator type 1 (AIRE-1). Patients with APS1 suffer from mucocutaneous candidiasis and a number of organ-specific autoimmune diseases. Characteristic is a high variability in the number and character of the disease components in APS1, indicating that other genetic and environmental factors may strongly modulate the outcome of disease. Environmental factors may comprise chemical influences, such as nutritional compounds and drugs, or virus infections. Several drugs or chemicals were shown to induce hepatitis with autoimmune involvement, e.g. tienilic acid, dihydralazine and halothane. Adduct formation of an activated metabolite is believed to act as a trigger and to induce a specific immune response. Similarly, viruses were repeatedly shown to trigger autoimmune hepatitis. In virus infections, sequence similarities between viral and self-proteins may trigger autoimmune processes and the simultaneous presence of inflammatory cytokines during virus infection may further increase the risk of developing self-perpetuating autoimmune reactions which overshoot.

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.

Genetic heterogeneity in susceptibility to autoimmune hepatitis types 1 and 2

OBJECTIVE

Susceptibility to autoimmune hepatitis (AIH) type 1 has been associated with DRB1*03, DRB1*04, and DRB3 alleles in European and North-American whites, with DRB1*04 in Japan, and with DRB1*04 and DRB1*13 in Latin America. Very few studies have been performed on AIH type 2. The aim of the present study was to evaluate the association of AIH types 1 and 2 with HLA-DR and DQ loci.

METHODS

We performed HLA-DRB and -DQB1 typing by polymerase chain reaction amplification with sequence-specific primers (PCR-SSP) in 139 AIH patients. Most had AIH type 1 associated with circulating anti-smooth muscle antibody with F-actin specificity or antinuclear antibody. Twenty-eight patients presented AIH type 2 with anti-liver/kidney microsome type 1 or anti-liver cytosol type 1 antibodies.

RESULTS

We observed a significant increase of DRB1*13 (70% vs 26% of controls, p < 0.00001) and DRB3 (93% vs 69% of controls, p < 0.00001) in AIH type 1 patients. Analysis of patients without DRB1*13 disclosed a secondary association with DRB1*03 (70% vs 30% of controls, p = 0.0001) and either the DRB1*13 or the DRB1*03 alleles were present in the majority of these patients (91% vs 48% of controls, p = 0.001). Comparison of DRB1*13- and DRB1*03-positive subjects revealed that the former alleles conferred susceptibility to younger patients with AIH type 1. DQB1 typing showed a significant increase in DQB1*06 (68% vs 41% of controls, p = 0.00007) in strong linkage disequilibrium with DRB1*13, and a decrease in DQB1*0301 (8% vs 47% of controls, p(c) = 0.0003). On the other hand, HLA typing of patients with AIH type 2 disclosed a significant increase in the DRB1*07 (68% vs 20% of controls, p(c) < 0.00014), DRB4 (79% vs 43% of controls, p(c) = 0.004), and DQB1*02 (86% vs 42%, p = 0.00002) alleles. After exclusion of DRB1*07, a secondary association with HLA-DRB1*03 was further observed in these patients (78% vs 30%, p = 0.007) and most of them had either DRB1*07 or DRB1*03 (93% vs 44% of controls, p(c) < 0.0001).

CONCLUSIONS

Our data indicate that predisposition to AIH types 1 and 2 is associated, respectively, with the DRB1*13 or DRB1*03 and DRB1*07 or DRB1*03 alleles, and suggest that protection against type 1 disease may be conferred by DQB1*0301. In addition, the cluster of DRB1*13 in children with AIH type 1 also supports the concept that different HLA alleles might influence the onset of the disease.

Auto-antibodies in hepatitis C

Hepatitis C virus (HCV) has been implicated in the development of a variety of autoimmune phenomena, some of which are well documented and include a panel of auto-antibodies shared with autoimmune hepatitis (AIH). Anti-nuclear (ANA) and smooth muscle (SMA) antibodies (markers of AIH type 1 [AIH-1]), have been demonstrated in 9-38% and 5-91% of cases respectively, whereas anti-liver/kidney microsomal type 1 (anti-LKM-1) and anti-liver cytosol type 1 antibodies (anti-LC1) (markers of AIH type 2 [AIH-2]), are definitely rarer, especially in adults. The presence of these auto-reactivities in chronic hepatitis C generates clinical overlaps and dilemmas in the correct classification and treatment of such patients. The immunopathological characterization of the auto-antibodies, anti-nuclear and smooth muscle antibodies in particular, combined with internationally defined criteria for the diagnosis of AIH is helpful in this clinical process. Thyroid auto-antibodies and cryoprecitable rheumatoid factors are also commonly detected in hepatitis C, while the occurrence of other auto-antibodies still awaits confirmation.

Interferon therapy in LKM-1 positive patients with chronic hepatitis C: follow-up by a quantitative radioligand assay for CYP2D6 antibody detection

BACKGROUND/AIMS

Liver/kidney microsomal type 1 (LKM-1) antibodies described by indirect immunofluorescence using frozen sections of kidney, stomach and rat liver define a group of patients with type 2 autoimmune hepatitis. Sera react with a non-glycosylated 50-kD protein of the endoplasmic reticulum, which was recently identified as cytochrome P4502D6 (CYP2D6). LKM-1 antibodies may also be associated with hepatitis C virus infection (HCV+/LKM-1+). For this subset of patients, the choice of steroids or interferon alpha therapy may be difficult because of the association of hepatitis C virus infection and autoimmune manifestations. Recently we developed a quantitative immunoprecipitation radioligand assay using 35S-methionine-labeled CYP2D6 protein produced by in vitro transcription and translation reaction. This method detects antibodies against linear and conformational epitopes in both AIH-2 and HCV+/LKM-1+ patients. The aim of this study was to analyze the time-course of HCV+/LKM-1+ patients, applying our radioligand assay over a long follow-up.

METHODS

We studied five patients who were positive for CYP2D6 antibodies from among 235 chronic hepatitis C virus hepatitis patients (2.1%) treated with interferon alpha for a minimal follow-up of 2 years. We analyzed LKM-1 antibody titer sequentially by radioligand assay, HCV RNA titer and alanine aminotransferase activity in these patients.

RESULTS

We found no aggravation of liver disease in this group of patients. Three of these patients showed a sustained biochemical and virological response after interferon. Two others responded partially to interferon therapy. Alanine aminotransferase levels and HCV-RNA decreased during interferon therapy in responder patients. CYP2D6 antibodies did not change in three responder patients during follow-up. One responder patient decreased CYP2D6 antibody level by radioligand assay, but indirect immunofluorescence titers showed a similar pattern. One partial responder patient decreased CYP2D6 antibody level but was negative by indirect immunofluorescence.

CONCLUSIONS

Our results show that patients with hepatitis C virus who are positive for CYP2D6 antibodies may be treated with interferon, and respond in the same way as CYP2D6 antibody negative patients. Radioligand assay could be helpful for monitoring HCV+/LKM-1+ patients receiving interferon therapy.