Cytochrome P450IID6-specific CD8 T cell immune responses mirror disease activity in autoimmune hepatitis type 2

Autoimmune Hepatitis: Clinical Review with Insights into the Purinergic Mechanism of Disease

Autoimmune hepatitis (AIH) is an important disorder that predominantly results in inflammatory liver disease in genetically predisposed women. The clinicopathological picture is characterized by symptoms associated with both systemic inflammation and hepatic dysfunction, and with increased serum aminotransferases, elevated IgG, autoantibodies, and interface hepatitis on liver biopsy. AIH usually results in liver injury as a consequence of chronic hepatitis and cirrhosis. However, rarely, patients may present with fulminant liver failure. Early diagnosis is important in all instances because the disease can be highly responsive to immunosuppressive therapeutic options. Left untreated, the disease is associated with high morbidity and mortality. Here we provide an overview of the current state of knowledge on AIH and summarize the treatment options for this serious condition in adults. We also discuss the pathogenesis of the disease as a possible consequence of autoimmunity and the breakdown of hepatic tolerance. We focus on regulatory T cell impairments as a consequence of changes in CD39 ectonucleotidase expression and altered purinergic signaling. Further understanding of hepatic tolerance may aid in the development of specific and well-tolerated therapies for AIH.

Liver immunology

The liver is the largest organ in the body and is generally regarded by nonimmunologists as having little or no lymphoid function. However, such is far from accurate. This review highlights the importance of the liver as a lymphoid organ. Firstly, we discuss experimental data surrounding the role of liver as a lymphoid organ. The liver facilitates tolerance rather than immunoreactivity, which protects the host from antigenic overload of dietary components and drugs derived from the gut and it is instrumental to fetal immune tolerance. Loss of liver tolerance leads to autoaggressive phenomena, which if not controlled by regulatory lymphoid populations, may lead to the induction of autoimmune liver diseases. Liver-related lymphoid subpopulations also act as critical antigen-presenting cells. The study of the immunological properties of liver and delineation of the microenvironment of the intrahepatic milieu in normal and diseased livers provides a platform to understand the hierarchy of a series of detrimental events that lead to immune-mediated destruction of the liver and the rejection of liver allografts. The majority of emphasis within this review will be on the normal mononuclear cell composition of the liver. However, within this context, we will discuss selected, but not all, immune-mediated liver disease and attempt to place these data in the context of human autoimmunity.

Autoimmune hepatitis: Contrasts and comparisons in children and adults - a comprehensive review

This review concentrates on autoimmune hepatitis (AIH), a liver disorder affecting both children and adults, characterized by inflammatory liver histology, elevated transaminase levels, circulating non-organ-specific autoantibodies, and increased levels of immunoglobulin G, in the absence of a known aetiology. Two types of AIH are recognized according to seropositivity: smooth muscle antibody and/or antinuclear antibody define AIH type 1, while antibodies to liver-kidney microsome type 1 and/or liver cytosol type 1 define AIH type 2. AIH type 1 affects both adults and children, while AIH type 2 is mainly a paediatric disease, though it does occasionally affects young adults. There is a female predominance in both types. AIH is particularly aggressive in children/adolescents, progressing rapidly unless immunosuppressive treatment is started promptly. With appropriate treatment 80% of patients achieve remission and long-term survival. In childhood/adolescence, sclerosing cholangitis with strong autoimmune features, including interface hepatitis and serological features identical to AIH type 1, is as prevalent as AIH, but it affects boys and girls equally. The differential diagnosis relies on cholangiographic studies. In autoimmune sclerosing cholangitis, liver parenchymal damage responds satisfactorily to immunosuppressive treatment, whereas bile duct disease progresses in 50% of cases, leading to a worse prognosis and higher transplantation requirement; it has a higher recurrence rate after transplant than AIH. AIH can arise de novo in patients transplanted for non-autoimmune liver disease. Post transplant de novo AIH affects children and adults and responds well to the same treatment schedule used for classical AIH, but not to that used for acute rejection.

Promotion and prevention of autoimmune disease by CD8+ T cells

Until recently, little was known about the importance of CD8+ T effectors in promoting and preventing autoimmune disease development. CD8+ T cells can oppose or promote autoimmune disease through activities as suppressor cells and as cytotoxic effectors. Studies in several distinct autoimmune models and data from patient samples are beginning to establish the importance of CD8+ T cells in these diseases and to define the mechanisms by which these cells influence autoimmunity. CD8+ effectors can promote disease via dysregulated secretion of inflammatory cytokines, skewed differentiation profiles and inappropriate apoptosis induction of target cells, and work to block disease by eliminating self-reactive cells and self-antigen sources, or as regulatory T cells. Defining the often major contribution of CD8+ T cells to autoimmune disease and identifying the mechanisms by which they alter the pathogenesis of disease is a rapidly expanding area of study and will add valuable information to our understanding of the kinetics, pathology and biology of autoimmune disease.

Treatment of autoimmune liver disease: current and future therapeutic options

Autoimmune liver disease spans three predominant processes, from the interface hepatitis of autoimmune hepatitis to the lymphocytic cholangitis of primary biliary cirrhosis, and finally the obstructive fibrosing sclerotic cholangiopathy of primary sclerosing cholangitis. Although all autoimmune in origin, they differ in their epidemiology, presentation and response to immunosuppressive therapy and bile acid based treatments. With an ongoing better appreciation of disease aetiology and pathogenesis, treatment is set ultimately to become more rational. We provide an overview of current and future therapies for patients with autoimmune liver disease, with an emphasis placed on some of the evidence that drives current practice.

Current concepts in the diagnosis and management of autoimmune hepatitis

Autoimmune hepatitis (AIH) is a progressive necroinflammatory liver disease associated with significant morbidity and mortality. Mainly affecting females, AIH has a varied clinical presentation from minor symptomatology to acute liver failure. The diagnosis should be considered in anyone with abnormal liver function tests. Diagnostic features include biochemical evidence of transaminitis, elevated IgG and positive autoantibodies. Liver biopsy may show interface hepatitis with portal-based plasma cell infiltrates. A clinical and pathological spectrum of disease exists with other autoimmune liver disease in rare cases. AIH responds promptly to immunosuppression therapy, including corticosteroids (prednis(ol)one or budesonide) with azathioprine. Treatment failure can be addressed with several second-line immunosuppressive agents. Liver transplantation remains a successful salvage therapy for acute autoimmune liver failure or treatment failure in chronic AIH complicated by synthetic dysfunction, portal hypertension or hepatocellular carcinoma.

Cutting edge: chronic inflammatory liver disease in mice expressing a CD28-specific ligand

Inflammation of the normally tolerant liver microenvironment precedes the development of chronic liver disease. Study of the pathogenesis of autoimmune liver diseases, such as autoimmune hepatitis (AIH), has been hampered by a lack of autochthonous chronic animal models. Through our studies of T cell costimulation, we generated transgenic mice expressing a ligand specific for the CD28 receptor, which normally shares ligands with the related inhibitory receptor CTLA-4. The mice spontaneously develop chronic inflammatory liver disease with several pathologies found in AIH, including elevated serum aminotransferases in the context of normal alkaline phosphatase and bilirubin levels, lymphocytic inflammation, focal necrosis, oval cell hyperplasia, and fibrosis. The prevalence of IFN-γ-producing CD8(+) T cells in the livers of transgenic mice suggests a role for autoimmune cytotoxicity in the chronic disease state. The CD28 ligand-specific transgenic mice will facilitate evaluation of CD8(+) T cell function in liver disease pathologies found in AIH.

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

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

The immunopathogenetic role of autoantibodies in canine autoimmune hepatitis: lessons to learn from human autoimmune hepatitis

Autoimmune hepatitis (AIH) is not a disease entity restricted to man, but it can be found in other animals including canines. An increasing number of studies have focused on the immunopathogenesis of human autoimmune hepatitis (hAIH), but little is known of what triggers canine autoimmune hepatitis (cAIH). Several drugs, toxins, microbial and viral agents are able to induce autoantibodies and indeed immune-mediated chronic canine hepatitis with immunological and serological features similar of those seen in the human disease. We discuss the features of cAIH paying attention to the autoantibody profile of the disease in comparison to that seen in hAIH. We also discuss the immunomodulatory role of specific molecular signaling pathways such as those mediated by tumor growth factor and p38 mitogen-activated kinase in the induction of AIH, and the potential of these molecules to act as targets of specialized immunotherapeutic interventions. Review of the literature indicates that we have more to learn for the delineation of autoantibody profile and the antigen-specific immunoregulatory mechanisms involved in the pathogenesis of cAIH from the human disease, rather than the other way around.

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

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

Mouse liver-specific CD8(+) T-cells encounter their cognate antigen and acquire capacity to destroy target hepatocytes

CD8(+) T-cell immune response to liver antigens is often functionally diminished or absent. This may occur via deletion of these autoaggressive T-cells, through the acquisition of an anergic phenotype, or via active suppression mediated by other cell populations. We generated a double transgenic model in which mice express CD8(+) T-cells specific for the lymphocytic choriomeningitis virus nucleoprotein (LCMV-NP) and LCMV-NP as a hepatic neo-autoantigen, to study the immunological response of potentially liver antigen autoaggressive CD8(+) T-cells. Autoreactive transgenic CD8(+) T-cells were analyzed for functionality and cytotoxic effector status. Despite severe peripheral deletion of liver-specific CD8(+) T-cells, a fraction of autoreactive NP-specific CD8(+) T-cells accumulate in liver, resulting in hepatocyte injury and production of auto-antibodies in both male and female mice. NP-specific intrahepatic T-cells showed capacity to proliferate, produce cytokines and up-regulate activation markers. These data provide in vivo evidence that autoreactive CD8(+) T-cells are activated in the liver and developed an inflammatory process, but require additional factors to cause severe autoimmune destruction of hepatocytes. Our new model will provide a valuable tool for further exploration of the immunological response involved in inflammatory liver diseases, including autoimmune hepatitis.

Predicting and preventing autoimmunity: the case of anti-mitochondrial antibodies

To be able to predict who will develop autoimmune disease would allow for early treatment which may dramatically alter the course of the disease. In some cases, it may also lead to prevention of the disease development. The prediction of disease development is based on the analysis of risk factors which have been associated with the disease in question. These factors include genetic susceptibility, as well as immunological and environmental factors. One autoimmune disease that may serve as a model for disease prediction is primary biliary cirrhosis (PBC), an autoimmune liver disease affecting the small- and medium-sized bile ducts. PBC could be an ideal model due to recent advances in elucidating its genetic associations. As well, a variety of immunological and environmental risk factors have been well established. Indeed, the presence of PBC-specific antimitochondrial antibodies and/or antinuclear antibodies has been shown to be predictor of disease development and possibly prognosis. This review will examine the current evidence which suggests that we may potentially be able to predict the development of PBC in some individuals. These concepts may also be applied to autoimmune diseases in general.

PSC, AIH and overlap syndrome in inflammatory bowel disease

Primary sclerosing cholangitis (PSC) is a progressive, cholestatic disorder characterised by chronic inflammation and stricture formation of the biliary tree. Symptoms include pruritus, fatigue and in advanced cases ascending cholangitis, cirrhosis and end-stage hepatic failure. Patients are at an increased risk of malignancy arising from the bile ducts, gallbladder, liver and colon. The majority (>80%) of Northern European patients with PSC also have inflammatory bowel disease (IBD), usually ulcerative colitis (UC). IBD commonly presents before the onset of PSC, although the opposite can occur and the onset of both conditions can be separated by many years. The colitis associated with PSC is characteristically mild although frequently involves the whole colon. Despite the majority of patients having relatively inactive colonic disease, paradoxically the risk of colorectal malignancy is substantially increased. Patients may also develop dominant, stenotic lesions of the biliary tree which may be difficult to differentiate from cholangiocarcinoma and the coexistence of IBD may influence the development of this complication. Ursodeoxycholic acid may offer a chemoprotective effect against colorectal malignancy and improve liver biochemical indices. Evidence of any beneficial effect on histological progression of hepatobiliary disease is less clear. High doses (∼25-30 mg/kg/d) may be harmful and should be avoided. Autoimmune hepatitis (AIH) is less common in patients with IBD than PSC, however, an association has been observed. A small subgroup may have an overlap syndrome between AIH and PSC and management should be individualised dependant on liver histology, serum immunoglobulin levels, autoantibodies, degree of biochemical cholestasis and cholangiography.

Role for mycobacterial infection in pathogenesis of primary biliary cirrhosis?

Primary biliary cirrhosis (PBC) is a progressive cholestatic liver disease characterized by the immune-mediated destruction of biliary epithelial cells in small intrahepatic bile ducts. The disease is characterized by circulating antimitochondrial antibodies (AMAs) as well as disease-specific antinuclear antibodies, cholestatic liver function tests, and characteristic histological features, including granulomas. A variety of organisms are involved in granuloma formation, of which mycobacteria are the most commonly associated. This has led to the hypothesis that mycobacteria may be involved in the pathogenesis of PBC, along with other infectious agents. Additionally, AMAs are found in a subgroup of patients with mycobacterial infections, such as leprosy and pulmonary tuberculosis. Antibodies against species-specific mycobacterial proteins have been reported in patients with PBC, but it is not clear whether these antibodies are specific for the disease. In addition, data in support of the involvement of the role of molecular mimicry between mycobacterial and human mitochondrial antigens as triggers of cross-reactive immune responses leading to the loss of immunological tolerance, and the induction of pathological features have been published. Thus, antibodies against mycobacterial heat shock protein appear to cross-recognize AMA-specific autoantigens, but it is not clear whether these autoantibodies are mycobacterium-species-specific, and whether they are pathogenic or incidental. The view that mycobacteria are infectious triggers of PBC is intriguing, but the data provided so far are not conclusive.

Cutting edge issues in autoimmune hepatitis

Autoimmune hepatitis is an inflammatory liver disease affecting mainly females and characterised histologically by interface hepatitis, biochemically by elevated transaminase levels and serologically by circulating autoantibodies and increased levels of immunoglobulin G. Autoimmune hepatitis responds to immunosuppressive treatment, which should be instituted as soon as diagnosis is made. Seropositivity for smooth muscle and/or antinuclear antibody defines type 1 autoimmune hepatitis, while positivity for liver kidney microsomal type 1 antibody defines type 2 autoimmune hepatitis. The aetiology of autoimmune hepatitis is unknown, though both genetic and environmental factors are involved in its expression. The major mechanism of liver damage involves immune reactions against host liver antigens that are not adequately controlled by defective regulatory T cells. Current research aiming at potentiating regulatory T cell function in vitro to reconstitute tolerance in vivo has given promising results.

Review article: overlap syndromes and autoimmune liver disease

BACKGROUND

Autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) all nestle within the family of autoimmune liver diseases, whereby the result of immune-mediated liver injury gives rise to varied clinical presentations. Some patients demonstrate a phenotype whereby there is evidence of either PBC or PSC together with overlapping features of AIH. Due to an absence of well-validated diagnostic criteria and a lack of large therapeutic trials, treatment of overlap conditions is empiric and extrapolated from data derived from the primary autoimmune liver diseases.

AIMS

To review overlaps in the context of autoimmune liver diseases.

METHODS

General and specific review of published articles using PubMed, Medline and Ovid search engines, alongside pre-existing clinical management protocols, guidelines, and the authors' own knowledge of the published literature.

RESULTS

The challenges in diagnosis, clinical presentation, determining natural history and outcome of overlaps are presented, as well as present-day management suggestions, some based on evidence, others on consensus and opinion.

CONCLUSIONS

Overlapping autoimmune features, be they clinical, serological, histological or radiological are not infrequent, but appropriate diagnosis remains hindered by a lack of standardised diagnostic criteria. Optimum care for those with suspected overlap should thus focus on attention to detail over the fundamental aspects of timely secure diagnosis of the dominant disease entity. Clinicians should counsel patients carefully with regard to the risks and benefits of treatment, bearing in mind the paucity of randomised and controlled outcome data for medical interventions.

Immunohistochemical phenotyping of the inflammatory infiltrate in de novo autoimmune hepatitis after liver transplantation in children

We have investigated the inflammatory infiltrate in post-transplant dn-AIH, a form of late insidious graft rejection, focusing on transcription factors defining effector and T-regs, using an antigen retrieval immunohistochemical method on archived liver tissue, and compared it with ACR and classical AIH. Paraffin-embedded liver biopsies from pediatric patients with dn-AIH (n = 10), ACR (n = 10), and AIH (n = 13) were selected randomly and stained using antibodies directed to CD4, CD8, T-bet (marker of Th1 polarization), GATA-3 (marker of Th2 polarization), FOXP3 (marker for T regulatory cells), IL-17, CD56 (NK cells), and perforin. Portal and lobular lymphocytic infiltrate was assessed semi-quantitatively. Prominent CD4, CD8, and T-bet positivity were present in both the lobular and portal infiltrate of all three conditions. Overall T-bet score of lobular inflammation in the dn-AIH group was lower than in the ACR and AIH groups (p = 0.02). In contrast, most samples showed absent or minimal GATA-3 positivity. FOXP3, CD56, IL-17, and perforin staining of mild to moderate severity were present in all three groups in both the portal and lobular infiltrate. A Th1 polarization of the inflammatory infiltrate characterizes dn-AIH, but also ACR and AIH.

Autoimmune hepatitis type 2 associated with an unexpected and transient presence of primary biliary cirrhosis-specific antimitochondrial antibodies: a case study and review of the literature

BACKGROUND

Unlike other autoimmune liver diseases, primary biliary cirrhosis (PBC) has never been reported in early childhood, while type 2 autoimmune hepatitis (AIH) is eminently a paediatric disease.

CASE PRESENTATION

We describe a case of type 2 AIH with serological positivity for PBC-specific anti-mitochondrial antibodies (AMA) in a 3-year old girl. We found this observation intriguing as AMA and indeed an overlap with PBC are virtually absent in Type 2 AIH, a pediatric form of AIH which is distinct precisely because it is characterized by pathognomonic anti-liver kidney microsomal type 1 (LKM-1) showing a remarkable antigen-specificity directed against cytochrome P4502D6. We also review the literature in relation to AMA positivity in paediatric age and adolescence. In our case, the presence of AIH-2-specific anti-LKM-1 and PBC-specific AMA was confirmed by indirect immunofluorescence (IIF), and immunoblotting and ELISA based on recombinant mitochondrial antigens. The clinical, laboratory and histological features of the child are given in detail. Interestingly the mother was AMA positive without other features of PBC. The child was successfully treated with immunosuppression and five years after the original diagnosis is on a low dose of prednisolone and azathioprine, with no signs of relapse. Anti-LKM-1 antibodies are still present in low titres. AMA were detectable for the first 4 years after the diagnosis and disappeared later.

CONCLUSION

This is the first case report in the literature of AIH type 2 with an unexpected PBC-specific AMA positivity in a young child. Response to immunosuppressive treatment was satisfactory and similar to that described in AIH. A review of published reports on AMA positivity in paediatric age shows that the antibody may arise in the context of immunodeficiency and is variably associated with liver damage.

Tuberculosis Is Not a Risk Factor for Primary Biliary Cirrhosis: A Review of the Literature

Primary biliary cirrhosis (PBC) is a progressive cholestatic liver disease characterised serologically by cholestasis and the presence of high-titre antimitochondrial antibodies, and histologically by chronic nonsuppurative cholangitis and granulomata. As PBC is a granulomatous disease andMycobacterium tuberculosisis the most frequent cause of granulomata, a causal relation between tuberculosis and PBC has been suggested. Attempts to find serological evidence of PBC-specific autoantibodies such as AMA have been made and, conversely, granulomatous livers from patients with PBC have been investigated for molecular evidence ofMycobacterium tuberculosis. This paper discusses in detail the reported data in support or against an association betweenMycobacterium tuberculosisinfection and PBC. We discuss the immunological and microbiological data exploring the association of PBC with exposure toMycobacterium tuberculosis. We also discuss the findings of large epidemiologic studies investigating the association of PBC with preexistent or concomitant disorders and the relevance of these findings with tuberculosis. Genome-wide association studies in patients with tuberculosis as well as in patients with PBC provide conclusive hints regarding the assumed association between exposure to this mycobacterium and the induction of PBC. Analysis of these data suggest thatMycobacterium tuberculosisis an unlikely infectious trigger of PBC.

Immunopathogenesis of primary biliary cirrhosis: an old wives' tale

Primary biliary cirrhosis (PBC) is a cholestatic liver disease characterised by the autoimmune destruction of the small intrahepatic bile ducts. The disease has an unpredictable clinical course, but may progress to fibrosis and cirrhosis. Although medical treatment with urseodeoxycholic acid is largely successful, some patients may progress to liver failure requiring liver transplantation. PBC is characterised by the presence of disease specific anti-mitochondrial (AMA) antibodies, which are pathognomonic for PBC development. The disease demonstrates an overwhelming female preponderance and virtually all women with PBC present in middle age. The reasons for this are unknown; however several environmental and immunological factors may be involved. As the immune systems ages, it become less self tolerant, and mounts a weaker response to pathogens, possibly leading to cross reactivity or molecular mimicry. Some individuals display immunological changes which encourage the development of autoimmune disease. Risk factors implicated in PBC include recurrent urinary tract infection in females, as well as an increased prevalence of reproductive complications. These risk factors may work in concert with and possibly even accelerate, immune system ageing, contributing to PBC development. This review will examine the changes that occur in the immune system with ageing, paying particular attention to those changes which contribute to the development of autoimmune disease with increasing age. The review also discusses risk factors which may account for the increased female predominance of PBC, such as recurrent UTI and oestrogens.

The benefit of animal models for autoimmune hepatitis

Autoimmune hepatitis (AIH) is a chronic liver disease which is normally recognized during late stage of the disease. Due to limited knowledge about the onset and course of disease and need for chronic immunosuppression with significant side-effects there is a requirement for a good preclinical animal model, mirroring main characteristics of AIH. In addition to the exclusion of other liver diseases, AIH is characterized by elevated serum transaminases, specific autoantibodies and elevated gammaglobulins as well as a specific liver histopathology. A good preclinical model should mirror most of these criteria. In the last decades several models have been published using different approaches to break hepatic tolerance and induce liver damage. The induction of a chronic hepatitis similar to the human disease remained a difficult challenge. Nevertheless, these models helped to get more information about the aspects of AIH induction and liver immunology.

Pathogenesis of autoimmune hepatitis

The mechanisms underlying the pathogenesis of autoimmune hepatitis are not fully understood, though there is growing evidence that genetic predisposition, molecular mimicry and/or impairment of regulatory T-cells are involved in the initiation and perpetuation of the autoimmune liver attack. The histological picture of interface hepatitis, characterized by a dense portal mononuclear cell infiltrate, was the first to suggest an autoaggressive cellular immune attack in the pathogenesis of this condition. Liver damage is likely to be orchestrated by CD4(pos) T-cells recognizing an autoantigenic liver peptide. For autoimmunity to arise, the peptide must be presented by antigen-presenting cells to naïve CD4(pos) T-helper (Th0) cells. Once activated, Th0-cells can differentiate into Th1-, Th2-, or Th17-cells, initiating a cascade of immune reactions that are determined by the cytokines they produce. Autoantigen recognition and the above effector mechanisms are opposed by regulatory T-cells, a cell subset numerically and functionally impaired in autoimmune hepatitis.

Epitope spreading of the anti-CYP2D6 antibody response in patients with autoimmune hepatitis and in the CYP2D6 mouse model

Autoimmune hepatitis (AIH) is a serious chronic inflammatory disease of the liver with yet unknown etiology and largely uncertain immunopathology. The hallmark of type 2 AIH is the generation of liver kidney microsomal-1 (LKM-1) autoantibodies, which predominantly react to cytochrome P450 2D6 (CYP2D6). The identification of disease initiating factors has been hampered in the past, since antibody epitope mapping was mostly performed using serum samples collected late during disease resulting in the identification of immunodominant epitopes not necessarily representing those involved in disease initiation. In order to identify possible environmental triggers for AIH, we analyzed for the first time the spreading of the anti-CYP2D6 antibody response over a prolonged period of time in AIH patients and in the CYP2D6 mouse model, in which mice infected with Adenovirus-human CYP2D6 (Ad-h2D6) develop antibodies with a similar specificity than AIH patients. Epitope spreading was analyzed in six AIH-2-patients and in the CYP2D6 mouse model using SPOTs membranes containing peptides covering the entire CYP2D6 protein. Despite of a considerable variation, both mice and AIH patients largely focus their humoral immune response on an immunodominant epitope early after infection (mice) or diagnosis (patients). The CYP2D6 mouse model revealed that epitope spreading is initiated at the immunodominant epitope and later expands to neighboring and remote regions. Sequence homologies to human pathogens have been detected for all identified epitopes. Our study demonstrates that epitope spreading does indeed occur during the pathogenesis of AIH and supports the concept of molecular mimicry as a possible initiating mechanism for AIH.

Autoimmune hepatitis

Autoimmune hepatitis (AIH) is an inflammatory liver disease that mainly affects females. It is characterized histologically by interface hepatitis, biochemically by increased aspartate and alanine aminotransferase levels, and serologically by the presence of autoantibodies and increased levels of immunoglobulin G. AIH affects both adults and children, and is particularly aggressive in the latter group. It is a relatively rare but devastating disease, which progresses rapidly unless immunosuppressive treatment is started promptly. With appropriate treatment 80% of patients achieve remission and long-term survival. Those patients who progress to end-stage liver disease because they are unresponsive or nonadherent to treatment, and those with fulminant liver failure (encephalopathy grade II-IV) at diagnosis, require liver transplantation. Seropositivity for smooth muscle and/or antinuclear antibodies defines type 1 AIH, while positivity for liver kidney microsomal type 1 antibodies defines type 2 AIH. The primary cause of AIH is unknown; however, considerable knowledge about the mechanisms of liver damage involved has been gathered over the past 30 years, which is likely to provide the basis for specific modes of treatment and a possible cure.

Autoimmune hepatitis: a review of current diagnosis and treatment

Autoimmune hepatitis (AIH) is a chronic inflammatory disorder characterized by periportal inflammation, elevated immunoglobulins, autoantibodies, and a dramatic response to immunosuppression. An environmental agent is hypothesized to trigger an immune-mediated attack directed against liver antigens in genetically predisposed individuals. A plethora of clinical presentations can be seen ranging from chronic indolent disease to fulminant hepatic failure, and diagnosis requires exclusion of other causes of liver disease. Corticosteroid therapy must be instituted early and modified in an individualized fashion. Treatment decisions are often complicated by the diverse clinical manifestations, uncertainty about natural history, evolving ideas about treatment end points, and a multitude of alternative immunosuppressive agents. Achieving normal liver tests and tissue is the ideal treatment end point, but needs to be weighed against the risk of side effects. Decompensated patients may benefit from early liver transplantation. Long-term prognosis is excellent with early and aggressive initiation of therapy. Our paper discusses AIH, giving a detailed overview of its clinical presentation, risk factors, immunopathogenesis, up-to-date diagnostic criteria, current updates in therapy with a brief discussion of AIH in pregnancy, and long-term implications for cirrhosis and hepatocellular carcinoma in AIH patients.

Identification of T cell epitopes on soluble liver antigen in Chinese patients with auto-immune hepatitis

AIM

To identify soluble liver antigen (SLA)-specific dominant epitopes and analyse the correlation between SLA-specific T cell response and the status of the disease.

METHODS

A cross-sectional analysis of SLA-specific T cell responses to 54 overlapping peptides covering the entire SLA sequence was performed using an interferon (IFN)-γ ELISpot assay in 31 patients with auto-immune hepatitis (AIH)-1, 15 patients with primary biliary cirrhosis, 16 hepatitis B virus, seven hepatitis C virus infection and 10 healthy subjects, in order to assess the correlation between SLA-specific T cell responses and the clinical outcome.

RESULTS

Soluble liver antigen-specific IFN-γ responses in AIH were significantly more frequent in AIH patients (58.1%) than those in controls (6.7% in PBC, P=0.001; 4.3% in hepatitis B/C, P<0.001 and 0% in healthy subjects, P=0.0015). Among 31 AIH patients, the frequency of recognition and the magnitude of response to SLA peptides in anti-SLA antibody-positive patients were higher and stronger than those negative for anti-SLA antibodies (P=0.02 and 0.037 respectively). We further analysed T-cell restriction and found that six individual SLA peptides (4, 9, 11, 12, 41 and 44) were recognized by CD4 T cells, and the most frequently recognized peptides were peptides 12 (61.1% of participants), followed by peptide 4 and peptide 44 (55.6 and 38.9% respectively). Moreover, a positive association was found between the breadth of recognition of SLA peptides and the indices of liver damage.

CONCLUSION

T cell response to SLA in Chinese patients with AIH is broad and associated with hepatocyte damage.

MDSC in autoimmunity

Myeloid derived suppressor cells (MDSC) were first described nearly two decades ago. Until recently, however, descriptions of MDSC populations were found almost exclusively in animal models of cancer or in cancer patients. Over the last few years, an increasing number of reports have been published describing populations of myeloid cells with MDSC-like properties in murine models of autoimmune disease. In contrast to the proposed deleterious role of MDSC in cancer--where these cells likely inhibit tumor immunity--in the context of autoimmunity, MDSC have the potential to suppress the autoimmune response, thereby limiting tissue injury. A logical corollary of this hypothesis is that a failure of endogenous MDSC to appropriately control autoimmune T cell responses in vivo may actually contribute to the pathogenesis of autoimmune disease.

Autoantigen-specific regulatory T cells, a potential tool for immune-tolerance reconstitution in type-2 autoimmune hepatitis

Effector CD4 and CD8 T cell immune responses to cytochrome P450IID6 (CYP2D6), the autoantigen of autoimmune hepatitis type 2 (AIH-2), are permitted by a numerical and functional impairment of CD4(pos) CD25(high) regulatory T cells (T-regs). We aimed to investigate whether T-regs specific for CYP2D6 immunodominant regions and restricted by the appropriate human leukocyte antigen (HLA)-DR molecule can be generated in patients with AIH-2 and can control CD4 and CD8 T cell effectors targeting identical or overlapping CYP2D6 regions. CYP2D6-specific regulatory T cells (CYP2D6 T-regs) were obtained from peptide-pulsed monocyte-depleted peripheral blood mononuclear cells of 17 patients with AIH-2, who were positive for the predisposing HLA-DR7 and/or HLA-DR3 alleles. Their antigen specificity was assessed by cytofluorimetry using HLA class II tetramers and their cytokine profile by intracellular staining. T-reg ability to suppress was ascertained by measuring reduction of CD4(pos) CD25(neg) cell proliferation/effector cytokine secretion and of CD8 T cell cytotoxicity. The most efficient suppression of effector T cell proliferation, inflammatory cytokine release, and cytotoxicity was obtained by coculturing T-regs with CYP2D6-peptide-loaded semimature dendritic cells (smDCs), and smDC-CYP2D6 T-regs also expressed high levels of FOXP3 (forkhead box P3). Possession of the appropriate HLA-DR molecule and recognition of the CYP2D6 autoantigenic sequence were critical to the synergistic smDC-CYP2D6 T-reg immunoregulatory functions, and lack of either element led to poor control of responder cell proliferation and cytokine secretion. Moreover, interferon-γ neutralization significantly boosted the suppressive ability of CYP2D6 T-regs.

CONCLUSION

T-regs generated under CYP2D6-specific conditions and cocultured with smDCs are highly effective at controlling autoreactive T cells, thus providing the basis for a powerful and tailored form of immunotherapy for AIH-2.

Primary biliary cirrhosis and autoimmune hepatitis: apotopes and epitopes

Autoimmune liver diseases (ALDs) represent a wide spectrum of chronic inflammatory diseases that are characterized by an immune-mediated attack against either hepatocytes (in the case of autoimmune hepatitis types 1 and 2, AIH-1, 2) or cholangiocytes (in primary biliary cirrhosis, PBC). PBC is considered a model autoimmune disease due to the homogeneity of patients, the high specificity of antimitochondrial antibodies (AMAs), and the specificity of biliary epithelial cell (BEC) destruction. It ensues from a multi-lineage loss of tolerance to the E2 component of the pyruvate dehydrogenase complex (PDC-E2). One of the major unanswered questions in the pathogenesis of PBC is the specificity of small intrahepatic bile duct attack while PDC-E2 is present in mitochondria of nucleated cells. Recent findings suggest that the apoptosis of BECs may be of considerable importance for understanding PBC, and that they are more than simply an innocent victim of an immune attack. Rather, they attract immune attack by virtue of the unique biochemical mechanisms by which they handle PDC-E2. The role of apoptotic cells in AIH is not well defined, but advances in the study of autoreactive T cells stem mostly from AIH type 2, where the main autoantigen (CYP2D6) is known, enabling the characterization of antigen-specific immune responses. This review article is intended to provide a critical overview of current evidence on tissue specificity in ALDs, as well as the characteristics of the relevant epitopes and apotopes and their biological and clinical significance.

Xenobiotic exposure and autoimmune hepatitis

Although genetics contributes to the development of autoimmune diseases, it is clear that "environmental" factors are also required. These factors are thought to encompass exposure to certain drugs and environmental pollutants. This paper examines the mechanisms that normally maintain immune unresponsiveness in the liver and discusses how exposure to certain xenobiotics such as trichloroethylene may disrupt those mechanisms and promote autoimmune hepatitis.

Conformational anti-cytochrome P4502E1 (CYP2E1) auto-antibodies contribute to necro-inflammatory injury in chronic hepatitis C

Circulating auto-antibodies against cytochrome P4502E1 (CYP2E1) have been observed in a significant fraction of patients with chronic hepatitis C (CHC). This study investigated the clinical significance of these auto-antibodies in relation to their antigen specificity. The presence of anti-CYP2E1 IgG was investigated in 137 consecutive patients with biopsy-proven CHC. Anti-CYP2E1 IgG above control threshold levels was detected in 52 (38%) subjects. By combined immunoprecipitation and western blotting, we observed that among anti-CYP2E1 IgG-positive sera, 23 (44%) were unreactive towards denaturated CYP2E1, indicating a prevalent recognition of conformational CYP2E1 antigens. Conformational anti-CYP2E1 auto-antibodies were unrelated to circulating gamma-globulins, alcohol intake or infection by specific HCV genotypes. The presence of anti-CYP2E1 auto-antibodies was associated with an 11-fold (OR 10.9 95%CI 1.4-86.6 P = 0.008) increased prevalence of necro-inflammatory grading ≥ 4 (Ishack's criteria) and 4-fold (OR 4.0; 95%CI 1.3-11-7: P = 0.014) increased prevalence of fibrosis staging ≥ 2, respectively. Multivariate analysis confirmed conformational anti-CYP2E1 IgG (P = 0.005) and age (P = 0.033) as independent predictors of necro-inflammatory grading ≥ 4. The development of anti-CYP2E1 auto-antibodies targeting conformational CYP2E1 epitopes is associated with more severe liver damage in CHC.

Type 1 T helper cells induce the accumulation of myeloid-derived suppressor cells in the inflamed Tgfb1 knockout mouse liver

Immune-mediated liver injury in hepatitis is due to activated T cells producing interferon-γ (IFN-γ). It is important to identify negative feedback immune mechanisms that can regulate T cell activity. In this study, we demonstrate that liver inflammation mediated by type 1 T helper (Th1) cells can induce the accumulation of myeloid-derived suppressor cells (MDSCs), pleiomorphic cells capable of modulating T cell-mediated immunity, that heretofore have been studied almost exclusively in the context of tumor-associated inflammation. Mice deficient in the gene encoding transforming growth factor-β1 (Tgfb1(-/-) mice) acutely develop liver necroinflammation caused by IFN-γ-producing clusters of differentiation 4-positive (CD4(+)) T cells. Liver Th1 cell accumulation was accompanied by myeloid cells expressing CD11b and Gr1, phenotypic hallmarks of MDSCs. Isolated Tgfb1(-/-) liver CD11b(+)Gr1(+) cells were functional MDSCs, readily suppressing T cell proliferation in vitro. Pharmacologic inhibitors of inducible nitric oxide (NO) synthase completely eliminated suppressor function. Suppressor function and the production of NO were dependent on cell-cell contact between MDSCs and T cells, and upon IFN-γ, and were specifically associated with the "monocytic" CD11b(+)Ly6G(-) Ly6C(hi) subset of liver Tgfb1(-/-) CD11b(+) cells. The rapid accumulation of CD11b(+)Gr1(+) cells in Tgfb1(-/-) liver was abrogated when mice were either depleted of CD4(+) T cells or rendered unable to produce IFN-γ, showing that Th1 activity induces MDSC accumulation.

CONCLUSION

Th1 liver inflammation mobilizes an MDSC response that, through the production of NO, can inhibit T cell proliferation. We propose that MDSCs serve an important negative feedback function in liver immune homeostasis, and that insufficient or inappropriate activity of this cell population may contribute to inflammatory liver pathology.

Breaking self-tolerance toward cytochrome P4502E1 (CYP2E1) in chronic hepatitis C: possible role for molecular mimicry

BACKGROUND & AIMS

Circulating auto-antibodies targeting conformational antigens on cytochrome P4502E1 (CYP2E1) are detectable in patients with chronic hepatitis C (CHC) and are associated with more severe necro-inflammation. This study investigated the antigen specificity and the possible origin of these auto-antibodies.

METHODS

CYP2E1 site-directed mutagenesis and molecular simulation were used to characterize the epitope specificity of CHC-associated anti-CYP2E1 auto-antibodies.

RESULTS

Immunoprecipitation experiments using differently mutated human CYP2E1s revealed that conformational anti-CYP2E1 antibodies targeted two epitopes located on the molecule surface in an area between Lys(324)-Glu(346) at J-K'' helices overlapping. Such epitopes were not recognized by the sera targeting linear CYP2E1 antigens. The CYP2E1(324-346) peptide showed good homology with two sequences (NS5b(438-449) and NS5b(456-465)) within the NS5b protein of hepatitis C virus (HCV). Consistently, conformational anti-CYP2E1 IgG bind to GST-conjugated NS5b(438-449) and NS5b(456-465) more efficiently than those recognizing CYP2E1 linear antigens. Competition experiments confirmed the cross-reactivity of conformational anti-CYP2E1 IgG with both NS5b(438-449) and NS5b(456-465). Moreover, mice immunized with GST-conjugated NS5b(438-449) or NS5b(456-465) peptides developed antibodies recognizing human CYP2E1.

CONCLUSIONS

In CHC patients cross-reactivity between CYP2E1 and specific sequences in HCV-NS5b protein can promote the development of auto-antibodies targeting conformational epitopes on the CYP2E1 surface that might contribute to hepatic injury.

Effects and regulation of autoreactive CD8+ T cells in a transgenic mouse model of autoimmune hepatitis

BACKGROUND & AIMS

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease of unknown etiology. Autoreactive T cells are thought to mediate liver injury, but the pathogenesis of AIH is poorly understood because of the lack of suitable animal models. We established a mouse model to investigate liver-specific T-cell responses and assess the effects and regulation of autoreactive CD8(+) T cells in the pathogenesis of AIH.

METHODS

We generated transgenic mice expressing the influenza virus hemagglutinin (HA) autoantigen under control of mouse albumin regulatory elements and alpha-fetoprotein enhancers (Alb) specifically in the liver (Alb-HA mice); they were crossed with mice that express a specific T-cell receptor (TCR) (CL4-TCR). CL4-TCR transgenic CD8(+) T cells were also adoptively transferred into Alb-HA mice. We investigated immunologic mechanisms of CD8(+) T cell-induced liver damage and of counteracting peripheral tolerance.

RESULTS

The double-transgenic mice (Alb-HA/CL4-TCR) spontaneously developed chronic, autoimmune-mediated hepatitis, characterized by necroinflammatory lesions, hepatic fibrosis, and increased levels of aminotransferase; these features resembled those of AIH. Interestingly, most liver-infiltrating, HA-specific CD8(+) T cells had an anergic phenotype; regulatory CD4(+)CD25(+)Foxp3(+) T cells accumulated in the inflamed liver.

CONCLUSIONS

The continuous development of a few, HA-specific CD8(+) effector T cells is sufficient to induce chronic hepatitis. Peripheral tolerance mechanisms such as induction of T-cell anergy and accumulation of regulatory CD4(+)CD25(+)Foxp3(+) T cells protect the liver from severe damage. Our mouse model that spontaneously develops chronic autoimmune-mediated hepatitis provides a new tool to investigate autoantigen-specific T-cell responses and regulatory mechanisms involved in the prevention and pathogenesis of AIH.

Autoimmune hepatitis: new paradigms in the pathogenesis, diagnosis, and management

Autoimmune hepatitis (AIH), primary biliary cirrhosis, and primary sclerosing cholangitis are the three major autoimmune diseases affecting the liver, and of these three, AIH is the most typical autoimmune disease being characterized by a T-cell-rich infiltrate, raised circulating γ-globulins, autoantibodies, HLA associations, and links with other autoimmune diseases. It is the only one, of the three diseases, that responds well to immunosuppressive therapy. AIH is caused by dysregulation of immunoregulatory networks and the consequent emergence of autoreactive T cells that orchestrate a progressive destruction of hepatocytes leading untreated to liver failure. T cells play a major role in the immunopathogenesis, and both CD4(+) and CD8(+) T cells are involved together with effector responses mediated by NK cells, γδ T cells, and macrophages. A number of triggering factors have been proposed including viruses, xenobiotics, and drugs, but none have been conclusively shown to be involved in pathogenesis.

Cytochrome P450 2D6 as a model antigen

Cytochrome P450 2D6 (CYP2D6) has been identified as the major autoantigen in type 2 autoimmune hepatitis (AIH). However, because of a lack of appropriate animal models, the etiology of AIH is still poorly understood. We generated a mouse model for AIH using the human CYP2D6 as a triggering molecule for autoimmunity. We infected wild-type FVB mice with an adenovirus expressing human CYP2D6 (Ad-2D6) to break self-tolerance to the mouse CYP2D6 homologues. Ad-2D6-infected mice showed persistent features of liver damage including hepatic fibrosis, cellular infiltrations, focal-to-confluent necrosis and generation of anti-CYP2D6 antibodies, which predominantly recognized the identical immunodominant epitope recognized by LKM-1 antibodies from AIH patients. Interestingly, Ad-2D6 infection of transgenic mice expressing the human CYP2D6 (CYP2D6 mice) resulted in delayed kinetics and reduced severity of liver damage. However, the quantity and quality of anti-CYP2D6 antibodies was only moderately reduced in CYP2D6 mice. In contrast, the frequency of CYP2D6-specific CD4 and CD8 T cells was dramatically decreased in CYP2D6 mice, indicating the presence of a strong T cell tolerance to human CYP2D6 established in CYP2D6 mice, but not in wild-type mice. CYP2D6-specific T cells reacted to human CYP2D6 peptides with intermediate homology to the mouse homologues, but not to those with high homology, indicating that molecular mimicry rather than molecular identity breaks tolerance and subsequently causes severe persistent autoimmune liver damage. The CYP2D6 model provides a platform to investigate mechanisms involved in the immunopathogenesis of autoimmune-mediated chronic hepatic injury and evaluate possible ways of therapeutic interference.

Aetiopathogenesis of autoimmune hepatitis

Interface hepatitis, histological hallmark of autoimmune hepatitis (AIH), is a dense portal mononuclear cell infiltrate invading the parenchyma, consisting of CD4 and CD8 T-lymphocytes, monocytes/macrophages and plasma cells. What triggers AIH is unknown, but there is evidence that failure of immune homeostasis plays a permissive role allowing liver autoantigen-specific cells to attack hepatocytes. Damage is likely to be orchestrated by CD4 T-lymphocytes recognizing an autoantigenic liver peptide. For autoimmunity to arise, the peptide, embraced by an HLA class II molecule, must be presented to naïve CD4 T-helper (T(H)0) cells by professional antigen-presenting cells. Once activated, T(H)0 cells can differentiate into T(H)1 cells, which are pivotal to macrophage activation, enhance HLA class I expression, rendering liver cells vulnerable to CD8 T-cell attack, and induce HLA class II expression on hepatocytes; or into T(H)2 cells producing IL-4, IL-10 and IL-13, cytokines favouring autoantibody production by B-lymphocytes. Autoantigen recognition is tightly controlled by regulatory mechanisms, such as those exerted by CD4+CD25+ regulatory T-cells (T-regs). Numerical and functional T-reg impairment characterizes AIH, particularly during active disease. Advances in the study of autoreactive T-cells stem mostly from AIH type 2, where the main autoantigen, CYP2D6, is known enabling characterization of antigen-specific immune responses. Monocyte involvement in the autoimmune liver attack has been recently reported.

Vigorous activation of monocytes in juvenile autoimmune liver disease escapes the control of regulatory T-cells

Interface hepatitis, the histological lesion typical of autoimmune hepatitis (AIH), is composed of CD4 and CD8 T lymphocytes and of innate immunity cells, particularly monocytes. Studies in AIH have focused on autoreactive CD4 and CD8 T cells and impairment of CD4+CD25+ regulatory T cells (T-regs), whereas little is known about the role of monocytes and their relationship with T-regs. We have investigated 51 patients with autoimmune liver disease (AILD) and 27 healthy subjects, finding that monocytes were higher in number (P = 0.044), had a more vigorous spontaneous migration (P < 0.0005 in patients with inactive disease [ID], and P < 0.001 in those with active disease [AD]), displayed a higher tumor necrosis factor alpha (TNF-alpha) over interleukin (IL)-10 production (P = 0.07 in ID and P = 0.0005 in AD), and expressed higher levels of Toll-like receptor (TLR) 4 (P = 0.048 in ID and P = 0.03 in AD). Addition of conventional T-regs (cT-regs) in AILD enhanced monocyte migration (P = 0.05 in ID and P = 0.08 in AD), magnified TNF-alpha over IL-10 production (P = 0.0005 in ID and P = 0.006 in AD), and markedly increased TLR4 expression levels (P = 0.01 in ID and P = 0.004 in AD), whereas in normal subjects it either restrained or left unchanged monocyte function. Because a CD127-negative subpopulation within CD4+CD25+ T cells exerts the strongest regulatory activity, we performed additional experiments using purified CD4+CD25+CD127- T cells (true T-regs [tT-regs]). Addition of tT-regs to monocytes decreased monocyte migration (P = 0.03) and promoted IL-10 production (P = 0.009), leaving unchanged TLR4 expression in healthy subjects, whereas in patients with AILD it induced only a marginal increase in IL-10 production (P = 0.045 in ID and P = 0.13 in AD).

CONCLUSION

Monocyte overactivation and inability of cT-regs and tT-regs to restrain it may contribute to the loss of immune tolerance and perpetuation of the autoimmune attack in AILD.

Autoimmune hepatitis

Autoimmune hepatitis (AIH) is an inflammatory liver disease affecting mainly females and characterised histologically by interface hepatitis, biochemically by elevated transaminase levels and serologically by the presence of autoantibodies and increased levels of immunoglobulin G. AIH responds to immunosuppressive treatment, which should be instituted as soon as diagnosis is made. Seropositivity for smooth muscle and/or anti-nuclear antibody defines type 1 AIH, while positivity for liver kidney microsomal type 1 antibody defines type 2 AIH. The aetiology of AIH is unknown, though both genetic and environmental factors are involved in its expression. Immune reactions against host liver antigens are believed to be the major mechanism of liver damage.

End-organ damage in a mouse model of fulminant liver inflammation requires CD4+ T cell production of IFN-gamma but is independent of Fas

Fulminant inflammation in the liver is often accompanied by the accumulation of IFN-gamma-producing T cells. The BALB/c-Tgfb1(-/-) mouse exhibits extensive, spontaneously developing necroinflammation in the liver, accompanied by the accumulation of IFN-gamma-producing CD4(+) and CD8(+) T cells. Liver damage depends on the presence of an intact Ifng gene. We determined the relevant cellular source(s) of IFN-gamma. In Tgfb1(-/-) liver, CD4(+) T cells were more numerous than CD8(+) T cells and NK cells, and produced more IFN-gamma. Depletion of CD4(+) T cells eliminated both the elevation in plasma IFN-gamma and aspartate aminotransferase, whereas depletion of CD8(+) T cells did not. Rag1(-/-)Tgfb1(-/-) mice exhibited neither IFN-gamma elevation nor tissue damage, indicating that NK cells are not sufficient. IFN-gamma was required for strong overexpression of class II genes but not for CD4(+) T cell activation, oligoclonal expansion, or accumulation in the liver. The T cell inhibitory molecule PD-L1 was strongly expressed in Tgfb1(-/-) livers, ruling out a lack of PD-L1 expression as an explanation for aberrant liver T cell activation. Finally, whereas Tgfb1(-/-) CD4(+) T cells overexpressed Fas ligand, hepatocellular damage was observed in Fas(lpr/lpr)Tgfb1(-/-) mice, indicating that liver pathology is Fas independent. We conclude that liver damage in this model of fulminant autoimmune hepatitis is driven by CD4(+) T cell production of IFN-gamma, is independent of both CD8(+) T cells and the Fas ligand/Fas pathway, and is not explained by a lack of PD-L1 expression.

Serum autoantibodies against cytochrome P450 2E1 (CYP2E1) predict severity of necroinflammation of recurrent hepatitis C

We previously reported that autoantibodies against cytochrome P4502E1 (CYP2E1) are frequent in patients with chronic hepatitis C. As autoimmune reactions are increasingly detected after orthotopic liver transplantation (OLT), this study investigates prevalence and significance of anti-CYP2E1 autoantibodies in 46 patients with post-OLT recurrent hepatitis C. IgG against recombinant human CYP2E1 above the control threshold was detected in 19 out 46 (41%) sera collected immediately before OLT and in 15 out 46 (33%) sera collected at the time of the 12 months follow-up liver biopsy. Although anti-CYP2E1 reactivity was not modified by OLT, the patients with persistently elevated anti-CYP2E1 IgG (n = 12; 26%) showed significantly higher prevalence of recurrent hepatitis with severe necroinflammation and fibrosis than those persistently negative or positive only either before or after OLT. Moreover, the probability of developing severe necroinflammation was significantly higher in persistently anti-CYP2E1-positive subjects. Multivariate regression and Cox analysis confirmed that the persistence of anti-CYP2E1 IgG, together with a history of acute cellular rejection and donor age >50 years, was an independent risk factor for developing recurrent hepatitis C with severe necroinflammation. We propose that autoimmune reactions involving CYP2E1 might contribute to hepatic damage in a subgroup of transplanted patients with recurrent hepatitis C.

Deficiency of forkhead box P3 and cytotoxic T-lymphocyte-associated antigen-4 gene expressions and impaired suppressor function of CD4(+)CD25(+) T cells in patients with autoimmune hepatitis

AIM

Recently, forkhead box P3 (Foxp3), cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), glucocorticoid-induced tumor necrosis factor receptor family-related gene (GITR), and CD28 were identified as the key molecules that control the development and activation of CD4+CD25+ regulatory T cells (T-reg). We investigated the expression pattern of these molecules on T-reg, and investigated the ability of T-reg to produce cytokines in patients with autoimmune hepatitis (AIH).

METHODS

Fifteen patients with AIH and nine healthy patients were included. To determine the frequency of T-reg, a two-color flow cytometry analysis was performed. T-reg were isolated using immunomagnetic beads, and the mRNA levels of Foxp3, CTLA-4, GITR, and CD28 were quantified by real-time polymerase chain reaction (PCR). The ability of T-reg to produce interferon-gamma, interleukin (IL)-10, transforming growth factor-beta, and tumor necrosis factor-alpha after stimulation by OKT3 was evaluated by measuring the levels of mRNA in T-reg by real-time PCR.

RESULTS

The frequency of T-reg was increased in AIH. The mRNA levels of Foxp3 and CTLA-4 were significantly lower in AIH. The ability of T-reg to produce IL-10 was impaired in AIH.

CONCLUSION

We speculate that the inferiority of the Foxp3 and CTLA-4 gene expressions on T-reg results in the impaired suppressor function of T-reg, and eventually in the breakdown of self-tolerance.

New insights into autoimmune liver diseases

Autoinflammatory liver disease represents an important aspect of global hepatological practice. The three principal disease divisions recognized are autoimmune hepatitis, primary sclerosing cholangitis and primary biliary cirrhosis. Largely, but not exclusively, these diseases are considered to be autoimmune in origin. Increased recognition of outlier and overlap syndromes, changes in presentation and natural history, as well as the increased awareness of IgG4-associated sclerosing cholangitis, all highlight the limitations of the classic terminology. New insights continue to improve the care given to patients, and have arisen from carefully conducted clinical studies, therapeutic trials, as well as genetic and laboratory investigations. The challenges remain to treat patients before liver injury becomes permanent and to prevent the development of organ failure.