Differences in immune recognition of cytochrome P4502D6 by liver kidney microsomal (LKM) antibody in autoimmune hepatitis and chronic hepatitis C virus infection

LKM-1 antibody, which characterizes a subtype of autoimmune hepatitis (AIH), is also found in some patients with chronic hepatitis C virus (HCV) infection. It has been suggested that HCV initiates autoimmunity through molecular mimicry, because there is partial identity between HCV and cytochrome P4502D6 (CYP2D6), the putative target of LKM-1. Whether CYP2D6 is the target of LKM-1 in HCV-related liver disease, however, is controversial. To clarify this issue, we have studied by phage plaque assay and Western blot the reactivity to recombinant CYP2D6, isolated from a human liver cDNA library, in 55 patients with LKM-1, 18 (14 females, median age 12 years) anti-HCV-negative, with classical AIH, and 37 (27 females, median age 52 years) anti-HCV-positive. Reactivity to CYP2D6 was found in 72% of the anti-HCV-negative, but only in 27% of the anti-HCV-positive patients (P < 0.001), although immunofluorescence LKM-1 titres were similar in the two groups. In addition, to investigate whether the antibody responsible for the LKM-1 fluorescent pattern also reacts with CYP2D6, we have determined the specificity of LKM-1 antibodies present in the supernatant of lymphoblastoid B cell lines obtained from two patients with LKM-1-positive AIH. An oligo/monoclonal antibody thus generated gave both the typical fluorescent pattern and reacted with CYP2D6. Our results show that whilst antibodies producing the characteristic LKM-1 fluorescent pattern can react with CYP2D6, not all LKM-1-positive sera do so, particularly if obtained from patients with chronic HCV infection. This suggests that LKM-1 in HCV infection recognizes epitopes or antigens different from those targeted in AIH.     

HEPATIC DAMAGE AFTER EXPOSURE TO HALOTHANE IN MEDICAL PERSONNEL

Two surgeons, in whom liver damage developed after occupationalexposure to sub-anaesthetic doses of halothane, were found tohave a circulating antibody which reacted specifically withhalothane-altered hepatocyte membrane components. This antibodyhas been found previously only in those patients in whom severehepatic necrosis developed after exposure to halothane and inno other form of liver injury. It may provide a specific diagnosticmarker in patients in whom there are other possible causes ofliver damage and could, therefore, remove the need for a challengeexposure and its attendant risks.     

Viral hepatitis: virus/host interaction

Abstract   Hepatitis A virus is considered directly cytopathic to the liver cell. Severity of the liver damage is dictated by viral load. Acute infection is followed by sustained immunity to the virus. Hepatitis B (HBV) and C (HCV) viruses are noncytopathic, hepatotropic viruses that cause acute and chronic hepatitis and hepatoma. Cellular and humoral immune responses are responsible not only for viral clearance but also for hepatocyte damage. T-cell response to HBV is vigorous, polyclonal, and multispecific in acutely infected patients who clear the virus while it is weak and narrowly focused in chronically infected patients. It is mainly executed by cytotoxic T lymphocytes (CTL), which destroy infected hepatocytes and secrete antiviral cytokines that interrupt the HBV life cycle. T-cell response to HCV is strong and multispecific in both acutely and chronically infected patients. Whether HCV is susceptible to a cytokine-mediated type of control is unknown. The ability of HCV to persist despite a strong CTL response suggests that HCV is either less visible to the CTL or less responsive to cytokine-mediated antiviral signals than HBV. Both viruses, but especially HCV, have a high mutation rate, leading to the occurrence of variant viral genomes with growth advantage and the ability of escaping immune recognition.     

Autoimmune serology in liver disease: methodology and interpretation

Abstract   Accurate measurement of levels of autoantibodies in serum is critical for the diagnosis of autoimmune hepatitis. The major reactivities include anti-nuclear antibody (ANA), smooth muscle antibody (SMA), antibody to liver kidney microsomes type-1 (anti-LKM1); other relevant reactivities include antibodies to liver cytosol 1 (anti-LC1), soluble liver antigen (anti-SLA), and neutrophil cytoplasmic antigens (ANCA). In addition to the classical indirect immunofluorescence technique, automatic assays based on recombinant antigens are now available, which allow detection of antibodies not visible on immunofluorescence, like anti-SLA, and assist in the interpretation of at times problematic immunofluorescence patterns, like anti-LKM1 or anti-LC1.     

Autoimmune hepatitis: diagnostic and management challenges

Abstract   There are two main types of autoimmune hepatitis (AIH): AIH type 1, characterized by anti-nuclear (ANA) and/or anti-smooth muscle (SMA) antibodies; and AIH type 2, positive for anti-liver kidney microsomal antibody type 1 (LKM1). AIH type 1 affects equally adults and children, while AIH type 2 affects mainly children. There is a female preponderance for both; AIH type 1 is associated with the HLA haplotype DR3, while AIH type 2 is associated with DR7. In young patients, both types of AIH frequently present with features of acute hepatitis. The diagnosis must be suspected and the appropriate tests sought promptly, because treatment should be started as soon as possible to avoid rapid progression to cirrhosis and liver failure. Though new drugs have been used for the treatment of AIH, including ciclosporin A, the standard treatment with prednisolone, to which azathioprine may be added as a steroid sparing agent, remains the best, with excellent short and long term results. Treatment, however, has to be finely tuned, to avoid severe steroid side effects.     

'SZ like'α1-antitrypsin phenotypes in PI ZZ children with liver disease

Using high resolution isoelectric focusing, α1-antitrypsin phenotypes were studied in 106 individuals of the PI ZZ genotype including 71 with liver disease, 22 with chest disease and 13 healthy subjects. The resulting Z patterns were found to be highly variable. In the majority of cases (89/106) the maximum staining intensity was either in the most basic isoform or shared equally between two basic isoforms of the Z phenotype. However, in 17 cases there was a marked intensification of the more acidic isoforms resulting in a pattern which closely resembled the SZ phenotype. This 'SZ like' pattern occurred more frequently in the liver group (16/71) than the chest group (0/22) or healthy (1/13) controls. One possible consequence of the 'SZ like' pattern is confusion with the genuine SZ phenotype leading to misclassification. If this were so, there could be an erroneous exaggeration of the actual incidence of childhood liver disease associated with PI SZ.     

Approach to a child with chronic liver disease

Abstract   Chronic liver disease is suspected on the basis of clinical and laboratory features. The former include a positive past or family history for liver disease, a prolonged duration of what looks like an acute hepatitic illness, presentation with complications of portal hypertension, like bleeding varices or hypersplenism, signs of chronic liver disease on examination, like hard liver, splenomegaly, ascites, and cutaneous stigmata of chronic liver damage. Typical laboratory features are low albumin, prolongation of prothrombin time usually responsive to vitamin K, high gammaglobulins. Differential diagnosis of chronic liver disease requires specific laboratory tests for viral hepatitis, autoimmune liver disease, metabolic disorders and evaluation of the liver histology to confirm the diagnosis or to assess disease severity.     

Liver transplantation in metabolic liver diseases

Abstract   Two types of metabolic disorders are treated with transplantation: those associated with severe liver damage, like alpha-1 antitrypsin deficiency, progressive familial cholestatic syndromes, tyrosinaemia, glycogen storage diseases, or cystic fibrosis; and those in which the liver is structurally normal, but is genetically unable to produce an essential protein, usually an enzyme, with consequent lethal systemic disease, like Crigler-Najjar syndrome, familial hypercholesterolaemia, propionic acidaemia, or urea cycle defects. The first group of diseases, among which the most common is alpha-1 antitrypsin deficiency, are treated by substitution of the whole liver with the donor liver, while the second group can be treated by auxiliary transplantation, to provide sufficient production of the deficient protein by the donor liver segment, while the native liver provides a safety net should the transplant fail and remains available for possible future gene therapy. In recent years, attempts have been made to treat these conditions by isolated human hepatocyte transplantation, with temporary success.     

Overlap syndromes from pediatrics to adulthood

Abstract   Overlap syndromes are autoimmune conditions with mixed immunological, clinical and histological features. The most frequent overlaps are between primary biliary cirrhosis (PBC) and autoimmune hepatitis (AIH), and between AIH and sclerosing cholangitis (SC). True AIH/PBC overlap syndrome is rare and characterized by elevation of transaminases and immunoglobulin G (IgG), positive anti-smooth muscle antibodies and a liver biopsy showing interface hepatitis as well as changes typical of PBC. These patients respond to immunosuppressive treatment that must be given promptly, to avoid progression to liver failure. The so-called 'autoimmune cholangitis' defines a small group of patients with cholestatic and histological features of PBC but negative for anti-mitochondrial antibody (AMA) and positive for PBC-specific anti-nuclear antibody (ANA). The positivity for ANA in these patients is a consequence of the AMA negativity, since AMA masks ANA on immunofluorescence. These patients' clinical course and response to treatment resemble that of classical PBC. AIH/ASC overlap syndrome is characterised by elevated levels of IgG and circulating autoantibodies, including ANA, SMA and atypical perinuclear anti-neutrophil cytoplasmic antibody, in association with cholangiographic changes typical of SC. This condition affects in particular children and young adults and may represent the early stage of adult primary SC. The parenchymal liver inflammation responds satisfactorily to immunosuppression, while the bile duct damage may progress despite treatment.