Immunopathogenetic and therapeutic aspects of autoimmune hepatitis

Authors


Correspondence to: Dr R. Moreno-Otero, Unidad de Hepatología (planta 3), Hospital Universitario de la Princesa, Diego de León 62, E-28006 Madrid, Spain. E-mail: rmoreno@hlpr.insalud.es

Summary

Autoimmune hepatitis is a chronic, progressive liver disease that responds well to immunosuppressive therapy, but has a poor prognosis if untreated. Possible triggering factors include viruses, other autoimmune disorders and drugs. The molecular mechanisms contributing to the pathogenesis include: reactions of autoantibodies against their corresponding autoantigens; aberrant expression of histocompatibility antigen class I and II molecules, cell adhesion molecules and cytokines; increased oxidative stress; and the occurrence of angiogenesis. The prevalence of the disease is highest in Caucasians, Europeans and women. The natural history of autoimmune hepatitis shows a poor prognosis, with frequent progression to cirrhosis and hepatic insufficiency in untreated patients. The occurrence of hepatocellular carcinoma is rare and is found only in long-standing cirrhosis. Corticosteroids as monotherapy or in combination with azathioprine are the treatments of choice; different therapeutic schedules and particularities of treatment for pregnant women and children have been established. To avoid treatment-associated adverse effects, alternative therapies have been proposed, including ciclosporin, budesonide, tacrolimus, mycophenolate mofetil, ursodeoxycholic acid, methotrexate, cyclophosphamide, mercaptopurine and free radical scavengers. Liver transplantation is indicated for patients refractory to or intolerant of immunosuppressive therapy.

Introduction

Autoimmune hepatitis (AIH) is a chronic, progressive liver disease that responds well to immunosuppressive therapy, but has a poor prognosis if untreated.1 Although the origin is unknown, a characteristic feature is the association with immunological changes, such as hypergammaglobulinaemia, presence of autoantibodies and interface hepatitis, on histological examination. There is a strong genetic component in the disease, its prevalence being much higher in Caucasians, Europeans and women (female to male ratio, 4 : 1). The pathogenesis is most probably related to an immune reaction against hepatocellular autoantigens, but the precise mechanisms through which liver damage occurs are not fully understood. The natural history of AIH shows a poor prognosis, with frequent progression to cirrhosis and hepatic insufficiency in untreated patients. Hepatocellular carcinoma can develop in AIH in the absence of viral infection, although it is rare and occurs only in long-standing cirrhosis.2

AIH is usually associated with hypergammaglobulinaemia (mainly immunoglobulin G), the presence of several autoantibodies and other autoimmune disorders (in particular thyroiditis, rheumatoid arthritis and diabetes mellitus). Clinical, biochemical, immunological and histological features that allow the clear-cut differentiation of AIH from other chronic liver diseases are not always present.3 Therefore, an accurate diagnosis requires: (i) the exclusion of other potential causes of chronic liver disease; and (ii) an evaluation of the features suggestive of AIH. To this end, in order to unify diagnostic criteria, the International Autoimmune Hepatitis Group established a scoring system which allows the classification of individuals as probable or definite AIH patients based largely on the presence or absence of: (i) serum biochemical abnormalities; (ii) histology; (iii) viral serology; and (iv) autoantibodies.4 Additional factors, such as gender, history of drug and alcohol intake, other autoimmune diseases and response to therapy, are also taken into account.

The diagnostic hallmark of AIH is the presence of circulating autoantibodies, whose target autoantigens have been characterized to different extents. Autoantibody profiles are used as a means of subclassification of AIH into types 1, 2 and 3. They are markers of the disease and have not been shown to have a definite pathogenic role, although they react with different hepatic proteins that act as target autoantigens for tissue-infiltrating effector T lymphocytes. No clear correlation exists between distinct positivities or titres of autoantibodies and the severity of hepatocellular damage.5 Autoantibody patterns may have prognostic value, but little evidence exists that they could be used to select patients for individualized therapies; however, antibodies to actin have high specificity for AIH and characterize young patients in whom corticosteroid therapy commonly fails. Anti-dsDNA in antinuclear antibody-positive patients is associated with a poor immediate response to corticosteroids, and antibodies to asialoglycoprotein receptor are associated with histological activity and a propensity for relapse after corticosteroid withdrawal.5

Triggering agents in aih

The clinical development of AIH has been associated with different viral infections, but, in most cases, the mechanisms by which viruses may trigger AIH are unknown. The measles virus was implicated as an aetiological agent in elderly unvaccinated patients with AIH, based on the finding of its genome more frequently in the lymphocytes of affected patients than in those of controls.6 Some reports have documented the triggering of AIH after acute infections with hepatitis A7, 8 and hepatitis B9 viruses, and in one case after co-infection with the human immunodeficiency virus and hepatitis C virus.10 Infection with hepatitis C virus is associated with the emergence of autoimmune phenomena,11 but it is more controversial to consider hepatitis C virus as an important triggering factor for AIH, as polymerase chain reaction analysis has confirmed that only a small minority of patients with type 1 AIH have true hepatitis C virus infection.12, 13 However, it has been described that P450-IID6, one of the autoantigens recognized by anti-liver/kidney microsomal type 1 (anti-LKM-1) autoantibodies detected in type 2 AIH, presents interesting similarities and even homology with the hepatitis C virus genome, the GOR-47 antigen14 and herpes simplex virus type I.15 This suggests that a process of molecular mimicry may stimulate autoreactivity in a genetically susceptible host, leading to the subsequent initiation of the autoimmune response that takes place during AIH. Of note is the fact that some of the structures recognized by anti-LKM-1 autoantibodies also have similarities or homology with carboxypeptidase H, a putative target of islet cell autoantibodies in insulin-dependent diabetes mellitus, and with 21-hydroxylase, an autoantigen in Addison's disease, which may be implicated in the progression from isolated to multiple organ-specific autoimmune disorders.16 Another mechanism that has been described as probably being related to the triggering of AIH is an antigen-specific T-cell defect related to the control of autoreactivity to asialoglycoprotein receptor.17 All of this evidence suggests that molecular mimicry with viral proteins or with autoantigens from other autoimmune disorders could play a role in the development of AIH.

Drugs such as minocycline, isoniazid, α-methyldopa, hydralazine and nitrofurantoin, as well as toxins, may also precipitate AIH.18 In female patients with chronic hepatitis C and genetic susceptibility, a latent AIH may be triggered by immunostimulating effects during interferon-α therapy.19 Exacerbation or induction of extra-hepatic20 and hepatic21 autoimmune disorders is well known, and is probably associated with antibody-dependent cellular cytotoxicity or aberrant expression of histocompatibility antigens (HLA) with subsequent T-cell cytotoxicity.22

Immunopathogenesis of aih

The predominant histological finding of important numbers of mononuclear infiltrating cells in tissue lesion areas of the liver in AIH patients, in particular CD8+ T cells, mainly in inflamed portal tracts (Figure 1a), suggests that these lymphocytes can actively play a pathogenic role in areas of hepatic damage and necrosis. In addition, there are multiple data showing that a number of key molecules involved in the interaction between effector and target cell, and in the subsequent cytolytic process, are differentially expressed in the liver of AIH patients, implicating an immune reaction in the pathogenesis of the disease.

Figure 1.

Immunoperoxidase staining of liver sections from patients with autoimmune hepatitis (AIH). (a) Marked expression of CD8+ infiltrating lymphocytes in inflamed portal tracts (× 20). (b) The β2-microglobulin conformational epitope detected by the HP/1H8 monoclonal antibody is reactive not only in sinusoidal lining cells, but also in hepatocytes (× 40). (c) Intense positive hepatocellular intercellular adhesion molecule-1 staining, mainly in areas of periportal inflammation (× 20). (d) CD31+ endothelial cells, adopting a characteristic microvessel morphology, are detected in inflamed portal tracts (× 20).

HLA class I molecules

Normally, these molecules participate in immune reactions by binding to peptides derived from endogenously synthesized antigens, such as viral proteins in infected cells, and by presenting them primarily to CD8+ T cells. Data on whether these human major histocompatibility complex (MHC) molecules are expressed in liver tissue are somewhat controversial. Expression on normal hepatocytes was clearly demonstrated in some studies,23–27 but was undetectable in others.28–32 Discrepancies between the different studies may be at least partially attributed to the variable sensitivities of the techniques applied for detection and also to the fine specificity of the monoclonal antibodies used.23, 27, 33 It has been confirmed with different monoclonal antibodies that hepatocytes from normal liver and from patients with different liver diseases, including chronic hepatitis C and acute allograft rejection, express HLA class I heavy chain and β2-microglobulin epitopes.23, 34 Indeed, immunohistochemical staining of liver tissue from AIH patients with the monoclonal antibody HP-1H8, which recognizes a β2-microglobulin conformational epitope not detectable on normal hepatocytes, showed positivity in both hepatocytes and sinusoidal lining cells (Figure 1b).

HLA class II molecules

These molecules, which generally bind to peptides derived from an endocytosed antigen, and are primarily recognized by CD4+ T cells, are expressed on B cells, macrophages, dendritic cells, Kupffer cells, a variety of epithelial cells and activated T lymphocytes. During autoimmune processes, an aberrant expression of HLA class II molecules on cells that normally do not bear them may occur, potentially contributing to the pathogenesis of the diseases; for instance, there are some reports of the de novo expression of HLA class II antigens in hepatocytes of AIH patients.33, 35, 36

Autoantigens

The hepatocellular expression of HLA class I and II molecules is not sufficient to initiate an immune response: an autoantigen must necessarily be expressed on cell membranes to allow recognition by T cells, thus leading to the autoimmune reaction characteristic of AIH. At least two such hepatocellular surface antigens have been reported: (i) P450-IID6, the autoantigen recognized by anti-LKM-1 autoantibodies;15 and (ii) membrane-bound asialoglycoprotein receptor, a liver-specific membrane protein37, 38 that is unique to hepatocytes,39 and is preferentially expressed at high density on periportal hepatocytes.40 The surface expression of asialoglycoprotein receptor on hepatocytes has also been shown to be associated with high-titre circulating antibodies in AIH.37

Additional information refers to autoantibodies against a soluble liver antigen (anti-SLA) and against a cytoplasmic antigen shared by liver and pancreas (anti-LP), whose specific major autoantigens were initially believed to be glutathione S-transferase subunit proteins41 and liver cytokeratins 8 and 18, respectively; however, it has been shown that anti-SLA and anti-LP are one and the same autoantibody, and that it has a high specificity for AIH.42 The target autoantigen has been cloned, characterized and suggested to be a cytosolic UGA-suppressor tRNA-associated protein (tRNP(Ser)Sec complex), not specific to the liver.43, 44 Finally, another autoantibody has received some attention: anti-LC1, which reacts with a liver-specific cytosolic antigen.45 This antigen is not expressed on the surface of hepatocytes; however, as serum antibody titres parallel with liver disease activity,46 it has been suggested that anti-LC1 might also somehow participate in the pathogenetic mechanisms responsible for liver injury. Two possible molecular targets for this autoantibody have recently been identified: argininosuccinate lyase47 and formiminotransferase cyclodeaminase.48

Cell adhesion molecules

Under basal conditions, the adhesion molecules responsible for the initial antigen-independent interaction between cytotoxic T cells and target cells are expressed at very low levels, if at all. However, inflammatory mediators, including cytokines, cause the strong induction of some of these molecules. This can be observed in the case of AIH. For instance, intercellular adhesion molecule-1/CD54, a molecule restricted to sinusoidal lining cells and scattered mononuclear cells in normal liver,49–51 is strongly induced in hepatocytes of AIH patients, particularly in areas of periportal inflammation (Figure 1c). Intercellular adhesion molecule-1 is the target cell counter-receptor of the lymphocyte function-related antigen, LFA-1 (CD11c/CD18), a member of the β2-integrin subfamily expressed in leucocytes. The interaction between these two molecules is crucial for triggering the cellular immune reaction. Similarly, LFA-3/CD58 (the target cell counter-receptor of the T-cell molecule LFA-2/CD2), which is not detected in normal hepatocytes, has been shown to be clearly expressed in the hepatocellular membrane of AIH patients, particularly in those periportal and lobular areas which are more severely infiltrated.35, 50

All of this information regarding the enhanced intra-hepatic expression of lymphocyte activation antigens, as well as cellular and vascular adhesion molecules, in AIH, can be considered as further decisive evidence for a leading role of T-cell-mediated immune mechanisms in the pathogenesis of tissue damage in this disease.35, 52

Cytokines

Little is known about the repertoire of cytokines in the pathogenesis of AIH. Excessive or unbalanced cytokine production may be a mechanism for the abnormal stimulation of lymphocytes, including autoreactive cells.53–55 Some experimental models suggest a role for cytokines in breaking T-cell tolerance.54, 56 Other cytokines may serve as the effectors of tissue injury.53 Various cytokines have been implicated in the pathogenesis of liver diseases characterized by inflammation and fibrosis.57, 58Interleukin-4 is a growth and differentiation factor for T cells, in particular for lymphocytes of the T-helper-2 subset, and also causes increased expression of HLA class II molecules.59 Elevated interleukin-4 production by liver-infiltrating T cells has been described in AIH,60 as well as significantly increased levels of interleukin-4 in sera from these patients.59 There is also evidence that the chemokine interferon-inducible protein 10 is locally expressed in hepatocytes of AIH patients, and its serum levels are increased during the course of the disease.61Transforming growth factor-β1, a cytokine that is considered to be an important mediator of hepatic fibrogenesis, is also produced by hepatocytes, infiltrating inflammatory cells and non-parenchymal cells in the livers of AIH patients, and its levels are increased in their sera.62 However, these phenomena are not specific to AIH, because they have also been observed in other types of autoimmune and non-autoimmune chronic liver disease. In spite of all this evidence, no convincing examples exist of cytokine abnormalities being the initiating mechanism of AIH.

Novel pathogenic factors

Results from our laboratory demonstrate that the livers of AIH patients show an increased expression of inducible nitric oxide synthase, as well as nitrotyrosine (a result of the reaction between oxidant peroxynitrites and cellular proteins), in comparison with normal controls. This evidence suggests that oxidative damage to cellular structures may play a role in the pathogenesis of AIH.63

Another interesting finding in our laboratory is the formation of new vasculature in the inflamed portal tracts of AIH patients, as evidenced by staining with a monoclonal antibody against CD31 (a specific marker of endothelial cells), acquiring a typical tubular-like structure (Figure 1d). This preliminary observation suggestive of angiogenesis, or neovessel formation, has also been reported for other chronic liver diseases, such as viral hepatitis C,64 and reflects an adaptive mechanism by which the body tries to maintain an adequate local supply of oxygen and nutrients to inflammatory areas within the liver.

Genetic predisposition to aih

Patients with AIH and their families share a genetic background which favours the development of autoimmune diseases. However, in the absence of studies with homozygotic twins, the analysis of the extent to which genetic abnormalities may lead to the development of the disease is difficult. Several genes are believed to contribute to the genetic predisposition to develop AIH.18 By binding target peptides, MHC alleles may be a determinant of the risk of developing AIH and, most probably, participate in the pathogenesis of the disease. HLA-DR3 and HLA-DR4 alleles have long been proposed as risk factors for type 1 AIH in Caucasian patients and in patients from Japan, respectively.65–68 These alleles encode positions 67–72 of the DRβ polypeptide chain, with either lysine or arginine at position 71. This position is located at the edge of the α-helix of the antigen-binding groove, where it can interact with both the bound antigen and the T-cell receptor. Differences in a single amino acid at this position can affect the steric relationship between antigen and T cell, thus influencing the immunoreactivity of the effector cells responsible for the disease, and hence the risk, the variable clinical manifestations of type 1 AIH and the outcome after corticosteroid therapy.69 Lysine at position 71 is correlated with an increased risk for type 1 AIH in Caucasian patients.65, 67 Conversely, in patients from Japan, Argentina, Brazil and Mexico, arginine rather than lysine at position 71 is associated with an increased risk for type 1 AIH.70, 71

A further possible genetic subdivision (within the HLA-DR3 allotype-positive group) is suggested by the finding of a significantly increased frequency of HLA-B14 and of the silent complement gene C4AQ0 in patients with anti-LKM-1 antibodies.65 Possession of C4AQ0 is not, however, confined to this group. It is also found in a high proportion of patients with antinuclear antibody/smooth muscle antibody (SMA)-positive AIH.72, 73

Interestingly, the HLA-DR alleles affect not only the susceptibility, but also the severity of the disease. This is probably based on the ability of HLA-DR alleles to induce changes in the number of immunocytes by influencing one of the following variables: (i) the density of the antigen-presenting complexes on the surface of the antigen-presenting cells; (ii) the ability of CD4 T-helper cells to respond to multiple antigenic peptides presented by a single allele of the MHC; and (iii) the ability of different HLA-DR molecules to present the same peptide.74 It has been suggested that a minimal immunoreactive unit that can be shared by multiple antigenic peptides and HLA-DR alleles may be responsible for the increased susceptibility and severity of AIH in some individuals through mechanisms which are not fully understood. This theory is compatible with proposals that involve molecular mimicry and microbial, xenobiotic and environmental antigens as inducers of immunoreactivity.75

Finally, additional interesting genetic associations have been suggested with regard to the clustering of other immunological diseases in patients with type 1 AIH, a poor outcome after corticosteroid therapy or a better prognosis. An association with cytokine polymorphisms (especially of the tumour necrosis factor gene, TNFA*2), as well as with C4AQ0, has also been established.76 As cytokines may be responsible for immunoregulation in type 1 AIH patients, they could be related to prognosis and response to treatment.

Only limited data are available on the genetic background of AIH type 2, but associations of AIH type 2 with HLA-DR3 have been reported,77–79 as well as with HLA-B14, HLA-DQ2 and C4AQ0.65, 78, 79

Treatment of aih

AIH rarely undergoes spontaneous regression, and therefore the main goal of therapy is to modify the natural history of the disease. The treatment is intended to alleviate symptoms, improve serological markers, slow the hepatic inflammatory and fibrotic processes, prevent cirrhosis and, indeed, diminish mortality.80 All patients should be treated, regardless of the particular AIH type and mode of presentation, including those with mild forms of the disease and transaminases only slightly above normal values. However, some authors recommend individualization of therapy in patients with mild disease, based on quality of life parameters, rather than on threats to life.81 Patients for whom liver transplantation is often indicated include those with advanced cirrhosis, those with intractable ascites, intrinsic hepatic encephalopathy or variceal haemorrhage in the absence of cirrhosis, and those with known intolerance to medication whose disease deteriorates.82

The treatment of choice for AIH patients involves immunosuppression with glucocorticoids, as monotherapy or in combination with azathioprine.80–84 This therapy has been shown to decrease mortality due to the disease. However, although corticosteroids reduce the incidence of cirrhosis during initial therapy, especially in patients with bridging necrosis or multilobular necrosis at presentation,85 cirrhosis develops despite therapy in 37% of patients within 5 years and in 47% within 10 years.86

From a practical point of view, two types of treatment regimen can be distinguished: one aimed at achieving remission, and a second intended for maintenance. According to the recommendations of the International Autoimmune Hepatitis Group, remission (or complete response) is defined as: (i) either or both of the following: marked improvement of symptoms and normalization of serum aspartate transaminase or alanine transaminase, bilirubin and immunoglobulin values within 1 year and sustained for at least a further 6 months on maintenance therapy, or a liver biopsy specimen at some time during this period showing, at most, minimal activity; or (ii) either or both of the following: marked improvement of symptoms together with at least 50% improvement of all liver test results during the first month of treatment, with aspartate transaminase or alanine transaminase levels continuing to fall to less than twice the upper normal limit within 6 months during any reductions towards maintenance therapy, or a liver biopsy within 1 year showing only minimal activity.4

Some authors advocate that liver histology should be analysed due to the fact that normal serum aspartate transaminase and gammaglobulin levels do not always correctly predict the absence of interface hepatitis.87, 88 This is because morphological improvement lags behind clinical and laboratory improvement by 3–6 months.83 Minimal activity in biopsies collected during that time is also considered to be sufficient evidence of response (disappearance of interface hepatitis and improvement to non-specific or portal hepatitis). Furthermore, liver biopsy may provide additional important information, as the degree of histological improvement has been shown to be associated with the propensity for relapse after drug withdrawal as follows: normal histology is associated with a 20% relapse rate; improvement to unspecific hepatitis is associated with a 50% relapse rate; and persistence of interface hepatitis or piecemeal necrosis is associated with an 86% relapse rate. Patients with established cirrhosis invariably relapse after discontinuation of medication.86, 89

Examination of liver tissue is the only method for establishing remission of the disease, and it should be considered before the termination of therapy. Liver biopsy can grade the adequacy of the histological response, the risk of subsequent relapse and the need for additional treatment before drug withdrawal.90

Remission therapy

There is agreement as to the treatment of choice for remission of the disease: first-generation synthetic glucocorticoids, such as prednisone, prednisolone or methylprednisolone, together with azathioprine.81 Prednisolone is the active metabolite of prednisone, which is produced in the liver. In patients with severely affected liver function, therapeutic levels of the active compound might not be reached, thus possibly justifying the use of prednisolone. Prednisone interferes with the processes of T-cell recognition of autoantigens, intra-hepatic recruitment of lymphocytes and T-cell proliferation; it may also impair immunoglobulin G production from plasma cells, and may enhance non-antigen-specific suppressor T-cell function.91, 92 Azathioprine is a purine analogue that inhibits T-cell proliferation by interfering with nucleic acid metabolism.93 Azathioprine is not efficacious as monotherapy in inducing remission, but is usually combined with corticosteroids to maintain remission of the disease. This combination allows a decrease in the dose of corticosteroids, thus reducing their side-effects and achieving better results than with corticosteroids at high doses. There is some controversy about the initial dose of corticosteroids to be used, and as to whether azathioprine should be administered at the beginning of therapy, or rather after achieving remission.94 As azathioprine is administered in order to allow a reduction in the dose of corticosteroids, thus minimizing their side-effects, some authors find no advantage in combination treatment before that time. As azathioprine has a delay of several weeks until effects are observed, an alternative is to start administration as soon as AIH is diagnosed. In fact, the initial treatment schedule must be defined based on the type of clinical, biochemical and histological features of AIH at presentation.

In the case of corticosteroid monotherapy for an acute-type presentation of AIH, a daily induction dose of 1 mg/kg for 2 weeks is recommended, with a maximum dose of 60 mg/day (Figure 2). If a therapeutic response is observed and serum transaminases decrease, the dose may be gradually reduced (10 mg/week) to 10–15 mg/day. In the case of the diagnosis of AIH in patients with a mild chronic hepatic condition, or even presenting with cirrhosis, a lower dose of corticosteroids is required to achieve remission (20–30 mg/day). Once remission is attained, the dose may be gradually reduced to 5 mg/day. In order to avoid corticosteroid-induced side-effects, particularly in post-menopausal women and diabetics, a combination of lower doses of corticosteroids (30 mg/day, which may be gradually reduced to 5–10 mg/day for maintenance) with 50 mg/day azathioprine is recommended. This schedule is as efficacious in inducing remission as high-dose monotherapy with corticosteroids.

Figure 2.

Treatment schedules for autoimmune hepatitis (AIH) remission with monotherapy or combined therapy.

Only 13% of patients do not respond, show an incomplete response to treatment for remission or must be withdrawn from therapy due to adverse effects.95 For the rest, long-lasting remission may be achieved, but complete cure is rare.

Maintenance therapy

This is aimed at preventing relapse whilst keeping the immunosuppressant-associated secondary effects to a minimum. Relapses frequently appear following treatment interruption, even after years of administration. Relapses are defined as: (i) either or both of the following: an increase in serum aspartate transaminase or alanine transaminase levels of greater than twice the upper normal limit, or a liver biopsy showing active disease, with or without the reappearance of symptoms, after a ‘complete’ response as defined above; or (ii) reappearance of symptoms of sufficient severity to require increased (or re-introduction of) immunosuppression, accompanied by any increase in serum aspartate transaminase or alanine transaminase levels, after a ‘complete’ response as defined above.4

Patients experiencing relapse must be administered life-long immunosuppressant regimens, with low-dose prednisone and/or azathioprine (Figure 3).96, 97 Therefore, the basic goal of therapy is to determine the minimum dose capable of maintaining remission for as long as required. Serum transaminase levels represent the best parameter of response, and should be kept within normal levels or at least below twice the upper normal limit. Usually, the majority of patients (87%) can be managed with prednisone or prednisolone (2.5–10 mg/day), although undesirable side-effects may occur. Hence, maintenance treatment with azathioprine monotherapy (50–75 mg/day) is often preferred.81 However, a higher dose can be used, as it has been shown that prolonged treatment with 2 mg/kg azathioprine per day is efficacious and well tolerated for the long-term maintenance of remission.98 If this dose of azathioprine is not capable of maintaining stable remission, the addition of 5–7.5 mg prednisone is better than doubling the dose of azathioprine. In any case, the dose of azathioprine to be administered must be adjusted based on serum transaminase levels.

Figure 3.

Treatment schedules for autoimmune hepatitis (AIH) maintenance therapy.

The activity of AIH is mild in 10–30% of patients, and remission may persist after treatment interruption.80, 81 However, treatment should only be interrupted after a minimum of 2–4 years, and in a gradual manner, as premature or sudden interruption of therapy may lead to severe exacerbation of the disease. As a rule, treatment interruption is accepted under conditions of normalized serum levels of transaminases and gammaglobulin, and the absence of inflammatory activity in liver biopsy. Once treatment has been interrupted, close follow-up of the patient is crucial, as relapse normally occurs during the following year, but also after many years.

Complete cure, as shown by a disappearance of all clinical, biochemical and histological manifestations of the disease for at least 5 years, is observed in only 10% of treated patients.88 An additional 21% undergo remission for more than 6 months: they may show residual manifestations of disease and immunoreactivity, but they receive no medication and are fully functional.

Treatment-associated adverse effects

Treatment with corticosteroids is associated with well-known, dose-dependent side-effects, such as weight increase, facial rounding, striae and hirsutism due to the development of an iatrogenic Cushing syndrome.94, 95 Hyperglycaemic effects are also frequent. Therefore, special attention must be paid to diabetic patients, as well as to patients with metabolic bone disease triggered by the liver disease itself or associated with post-menopause. Hypertension, glaucoma, subcapsular cataracts, aseptic osteonecrosis, panniculitis, psychosis and growth retardation in children have also been described in association with corticosteroids.99, 100 Prolonged administration of high doses may also induce muscular atrophy and facilitate infections. There is no evidence that corticosteroids may have a direct carcinogenic or teratogenic potential, although a low but increased incidence of extra-hepatic neoplasms has been reported, probably secondary to the immunosuppressant mechanism of the drug.101 As extra-hepatic malignancy may be a risk of long-term immunosuppression, some authors recommend the maintenance of an active tumour surveillance programme in AIH patients.90 The side-effects of prednisone are proportional to the amount of free active metabolite in serum (it normally circulates bound to corticosteroid-binding globulin or albumin). Therefore, patients with low levels of serum albumin or high levels of bilirubin (which may displace prednisolone from its binding to albumin) must be carefully controlled.99, 102 These situations commonly occur in cirrhotic patients. Severe corticosteroid-induced adverse effects are observed in 44% of patients treated with prednisone as monotherapy, and in only 10% of patients treated with combination therapy.94, 95

For azathioprine, bone marrow disorders, including thrombopenia and leucopenia, are the most severe unwanted side-effects.95 As these are usually dose related and reversible, periodic haematological follow-up is recommended. Other complications described for this drug include acute pancreatitis, cholestatic hepatotoxicity with fibrosis, hepatic regenerative nodular hyperplasia and an increased susceptibility to infections. Although the mechanism of action of the drug might suggest a potential carcinogenic effect, no definitive study has demonstrated that the low doses used for remission maintenance in AIH may increase the risk of tumour development in the long term.95, 98

Patients with AIH should be tested for thiopurine methyltransferase (TPMT) activity prior to the initiation of azathioprine. Patients with normal TPMT activity or the wild-type genotype should receive the daily dose (2 mg/kg) that has proved to be efficacious in a controlled trial;98 those with intermediate TPMT activity or the heterozygote genotype should, at the onset, empirically receive a lower daily dose (1 mg/kg) and be monitored carefully; finally, patients with absent TPMT activity or homozygous for low-activity genotypes should only be treated with very low doses of azathioprine, and perhaps not at all.103 The measurement of TPMT activity in patients who have bone marrow suppression is recommended, as azathioprine can be used effectively at much lower doses than previously suggested.

Aih and pregnancy

Fertility seems to be reduced in AIH patients, but pregnancies are not infrequent. Adequate control of the disease with immunosuppressants contributes to the prevention of potential worsening of the hepatic condition due to pregnancy, thus allowing its successful completion.104 Post-partum vigilance is also required. It has been described that, in certain cases, remission of AIH may occur during pregnancy, although the mechanisms are unknown. Teratogenic effects of the most common immunosuppressants have not been demonstrated; however, it is advisable to administer only the minimum effective doses of corticosteroids and azathioprine. In addition, breast-feeding should be avoided, as both drugs may be excreted in the milk.

Aih and children

The expression of AIH is significantly different in children and in adults. According to Gregorio et al., 38% of paediatric AIH patients have anti-LKM-1 autoantibodies (as opposed to 3–4% of adult patients).105 In addition, 50–65% have an acute presentation, often fulminant, and about 69% of children with type 1 AIH and 38% of children with type 2 AIH have already undergone a cirrhotic process at initial presentation. As opposed to adult AIH patients, the response to immunosuppressive therapy in AIH children is frequently poor, but there are reports showing that ciclosporin may induce biochemical remission of the hepatic inflammatory/necrotic process in children with AIH.106, 107 Otherwise, urgent liver transplantation is normally required. When a fair response is observed, daily treatment with corticosteroids instead of alternate-day administration is preferred.

Therapeutic alternatives

Therapeutic alternatives have been developed during the last few years, as approximately 10% of AIH patients show no response to first-generation corticosteroids, a further 15% show incomplete partial response and in 13% of patients the treatment must be discontinued due to severe toxicity.

Ciclosporin (5–6 mg/kg daily)

This has been used anecdotally in corticosteroid-resistant or -intolerant patients.108–112 Treatment-naive children have also received the drug orally, as initial therapy, prior to the use of a conventional corticosteroid regimen.106, 107 Thirty-two children were treated with ciclosporin for 6 months, followed by combined low doses of prednisone plus azathioprine for 1 month, after which ciclosporin was discontinued.106 Two of the patients were withdrawn (one due to non-compliance and the other due to liver failure, with no improvement whilst on ciclosporin). In 25 (83%) of the remaining 30 patients, normal serum alanine transaminase levels were achieved with ciclosporin. Adverse effects were considered to be mild and disappeared after treatment discontinuation. Ciclosporin has not been compared with conventional treatments in randomized controlled trials, or incorporated into the standard management protocols. Its main drawback is the appearance of hypertension and nephrotoxicity, thus requiring careful monitoring of arterial blood pressure and serum creatinine during therapy.108

Budesonide (6–8 mg daily)

This is a second-generation synthetic glucocorticoid that undergoes a strong first-pass clearance in the liver and is processed to metabolites that are devoid of glucocorticoid activity.113 Budesonide improved laboratory indices and was well tolerated in a small, open-label study involving 13 patients treated during 9 months.114 These initial favourable results could not be extended to 10 patients who were corticosteroid dependent. They were treated with 3 mg thrice daily during a mean time of 5 ± 1 months (range, 2–12 months).115 Seven of these patients relapsed after prednisone withdrawal, deteriorated during therapy or became drug intolerant. Withdrawal symptoms also frequently complicated conversion from prednisone to budesonide treatment. The results of this pilot study of 10 corticosteroid-dependent patients demonstrated that budesonide was ineffective in allowing withdrawal of conventional corticosteroids; in addition, its side-effects mimicked those of first-generation corticosteroids.115 Budesonide could have the greatest therapeutic value in treatment-naive patients with mild disease.

Tacrolimus (3 mg twice daily)

This drug prevents the clonal expansion of cytotoxic T cells and impairs antibody production.116 It has been shown to improve serum aminotransferase and bilirubin levels after 3 months in an open-label treatment trial.117 Experience with this drug is limited and its therapeutic value in AIH has not yet been established. Therapy has not been followed by clinical, biochemical or histological remission, and most patients developed mild renal insufficiency and hyperkalaemia.117 The appropriate dose should be based on the patient's weight, renal function, liver function, blood levels of the drug and clinical response. Tacrolimus has not been assessed against prednisone in prospective clinical trials and the risk–benefit ratio of therapy is unknown.

Mycophenolate mofetil (1 g twice daily)

This has been shown to induce biochemical remission in five of seven patients with AIH in whom standard therapy was ineffective or poorly tolerated.118 The histological activity index in liver biopsies was improved after 7 months. Treatment was well tolerated, and only one patient with leucopenia required dose adjustment. Further studies to establish the efficacy of this drug have been endorsed at a single topic conference sponsored by the American Association for the Study of Liver Diseases.119

Ursodeoxycholic acid (13–15 mg/kg daily)

This drug decreases hydrophobic biliary acids and has cytoprotective effects. It has been shown to improve clinical and biochemical indices in eight treatment-naive patients treated for 2 years in Japan.120 In the four patients who underwent liver biopsy examinations, histological features of inflammation, but not those of fibrosis, were also improved. These favourable results were not achieved in a randomized, placebo-controlled treatment trial with 13–15 mg/kg daily in a group of corticosteroid-treated, non-responding patients.121 Treatment with ursodeoxycholic acid did not facilitate dose reduction or corticosteroid withdrawal; furthermore, it had no effect on the clinical outcome or histological activity. Future studies warrant a more thorough investigation of the treatment period and/or higher doses in naive patients before ursodeoxycholic acid can be incorporated into the standard therapy of AIH.

Methotrexate

There is only one case report of successful treatment of a type 1 AIH patient, not responsive to standard therapy, with methotrexate (7.5 mg orally per week).122

Cyclophosphamide

In the reported patients, the authors were able to induce remission with 1–1.5 mg/kg cyclophosphamide in combination with a tapering dose of corticosteroids, initiated at 1 mg/kg. After induction, the authors were able to maintain remission with low doses of corticosteroids (2.5–10 g/day), together with 50 mg/day of cyclophosphamide.123 Cyclophosphamide could be an alternative to azathioprine in AIH patients with severe side-effects due to intolerance to standard therapy.

Mercaptopurine

The efficacy of mercaptopurine (a metabolite of azathioprine) has been demonstrated in some AIH patients resistant to corticosteroids who showed hypersensitivity to azathioprine.124 The schedule consists of initial low doses (12.5–25 mg/day) of mercaptopurine in combination with corticosteroids, subsequently reduced to 1.5 mg/kg daily for maintenance.

Deflazacort

This is an oxazolinic derivative of prednisolone with fewer effects on bone and glucose metabolism, which also seems to be useful in maintaining remission in AIH.125 However, the efficacy and tolerance of deflazacort have not yet been tested in large cohorts of patients.

Free radical scavengers

As mentioned above, results from our laboratory suggest the involvement of oxidative stress in cellular damage during AIH.63 These findings may open up interesting possibilities for new therapeutic alternatives directed against this pathogenetic mechanism. However, past experiences with thymic extracts, d-penicillamine and flavonoids as anti-inflammatory agents and/or free radical scavengers for AIH showed no major success.126–128

Experimental approaches

These are more sophisticated and have only been tested in laboratory animals, or are undergoing pre-clinical development. They include immunological manipulation with anti-inflammatory cytokines, such as interleukin-10, monoclonal antibodies against tumour necrosis factor, competing peptides directed at the MHC class II–peptide–T-cell receptor complex, T-cell vaccination or antibodies against the protein product of the T-cell gene (TIRC7) that inhibits T-cell proliferation.129–131

Liver transplantation

Patients who are refractory to or intolerant of immunosuppressive therapy require orthotopic liver transplantation. Survival rates for AIH are excellent. The 5-year patient and graft survival after liver transplantation is in the range 83–92%; the 10-year survival after transplantation is 75%, with negative autoantibodies and hypergammaglobulinaemia normalization in all patients within 2 years.132, 133 Despite the intensive immunosuppression following liver transplantation, patients are at risk of recurrent AIH. This has been suggested to be related to the reactivation of memory T cells by specific antigens in the donor liver, through a mechanism not requiring MHC compatibility (such as recipient T-cell receptor activation by donor MHC molecules in the absence of endogenous peptide antigens; or by donor antigens processed and presented by the recipient's antigen-presenting cells). The elucidation of such mechanisms may contribute to the development of novel therapeutic alternatives. Recurrence does not usually appear until the degree of immunosuppression has been reduced several years after transplantation.134, 135 Recurrence of AIH is recognized in 17% of patients after 4.6 ± 1 years, especially in patients who are inadequately immunosuppressed.135, 136 It is typically managed satisfactorily by adjustments in the immunosuppressive regimen, a low maintenance dose of corticosteroids being a useful measure to reduce AIH recurrence in the transplanted graft. Recurrent disease rarely progresses to cirrhosis or results in graft failure.137, 138 Patients transplanted for AIH also appear to be at an increased risk for rejection. In one series of 32 patients, 75% had an average of 1.7 episodes of rejection, 39% of which required therapy with OKT3.136

Acknowledgements

The authors are grateful to Katalin Mayer for helpful suggestions and English language assistance. This study was supported in part by grant SAF2001-1414 (to R.M.O.) from Ministerio de Ciencia y Tecnología, Spain.

Ancillary