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

Anti-Tribbles homolog 2 (TRIB2) autoantibodies in narcolepsy are associated with recent onset of cataplexy

STUDY OBJECTIVE

Recent studies have found increased autoantibodies against Tribbles homolog 2 (anti-TRIB2) and anti-streptolysin O (ASO) in narcolepsy. In this study, we replicated this finding with a primary focus on recent onset cases.

PARTICIPANTS AND METHODS

Participants included (1) 90 cases with cataplexy, (2) 57 cases without cataplexy, and (3) 156 age-sex matched controls, including 73 human leukocyte antigen (HLA)-DQB1*0602 allele carriers. A radioligand binding assay was used to detect anti-TRIB2 antibodies.

RESULTS

Anti-TRIB2 antibodies were prevalent in HLA-DQB1*0602 positive cases with cataplexy (25.0% of 76) and rare in cases without cataplexy (3.5% of 57, OR = 9.2, 95% CI = 2.5 - 33.5, P = 6.0 x 10(-4)) or controls (4.5% of 156, OR = 7.1, 95% CI = 3.1 - 16.2, P = 9.3 x 10(-6)). Anti-TRIB2 positivity in controls was not associated with DQB1*0602. In DQB1*0602 narcolepsy-cataplexy cases, the presence of anti-TRIB2 was associated with short disease duration (2.3 years from cataplexy onset), with 41.0% positive in this group (OR = 7.4 versus cases with onset > 2.3 years, 95% CI = 1.9- 28.5, P = 9.0 x 10(-4)). Anti-TRIB2 positivity in 39 DQB1*0602 positive recent onset cases was associated with increased ASO antibody (> 200 IU) (OR = 6.2, 95% CI = 1.6 - 24.6, P = 0.01), but did not correlate with age, gender, or body mass index.

CONCLUSION

Anti-TRIB2 autoantibodies are strongly associated with narcolepsy close to cataplexy onset (< or = 2.3 years). Anti-TRIB2 was rarely found in cases without cataplexy or with distant onset.

Anti-Tribbles homolog 2 autoantibodies in Japanese patients with narcolepsy

STUDY OBJECTIVES

Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness and cataplexy. The association with human leukocyte antigen (HLA)-DQB1*0602 and T-cell receptor alpha locus suggests that autoimmunity plays a role in narcolepsy. A recent study reported an increased prevalence of autoantibodies against Tribbles homolog 2 (TRIB2) in patients with narcolepsy. To replicate this finding, we examined anti-TRIB2 autoantibodies in Japanese patients with narcolepsy.

DESIGN

We examined anti-TRIB2 autoantibodies against a full-length [35S]-labeled TRIB2 antigen in Japanese patients with narcolepsy-cataplexy (n = 88), narcolepsy without cataplexy (n = 18), and idiopathic hypersomnia with long sleep time (n = 11). The results were compared to Japanese healthy controls (n = 87). Thirty-seven healthy control subjects were positive for HLA-DRB1*1501-DQB1*0602. We also examined autoantibodies against another Tribbles homolog, TRIB3, as an experimental control.

MEASUREMENTS AND RESULTS

Autoantibodies against TRIB2 were found in 26.1% of patients with narcolepsy-cataplexy, a significantly higher prevalence than the 2.3% in healthy controls. We found that anti-TRIB3 autoantibodies were rare in patients with narcolepsy and showed no association with anti-TRIB2 indices. No significant correlation was found between anti-TRIB2 positivity and clinical information.

CONCLUSIONS

We confirmed the higher prevalence and specificity of anti-TRIB2 autoantibodies in Japanese patients with narcolepsy-cataplexy. This suggests a subgroup within narcolepsy-cataplexy might be affected by an anti-TRIB2 autoantibody-mediated autoimmune mechanism.

LKM1 autoantibodies in chronic hepatitis C infection: a case of molecular mimicry?

Anti-liver-kidney microsome type 1 (LKM1) autoantibodies directed against the cytochrome P450 2D6 (CYP2D6) are considered specific markers of type 2 autoimmune hepatitis, but are also found in 5% of sera from patients chronically infected by hepatitis C virus (HCV). Molecular mimicry between HCV proteins and CYP2D6 has been proposed to explain the emergence of these autoantibodies. Anti-LKM1 autoantibodies from hepatitis C-infected patients were affinity-purified against immobilized CYP2D6 protein and used to screen a phage display library. CYP2D6 conformational epitopes were identified using phage display analysis and the identification of statistically significant pairs (SSPs). Cross-reactivity between CYP2D6 and HCV protein candidates was tested by immunoprecipitation. Nineteen different clones were isolated, and their sequencing resulted in the mapping of a conformational epitope to the region of amino acids 254-288 of CYP2D6. Candidate HCV proteins for molecular mimicry included: core, E2, NS3 and NS5a. Affinity-purified autoantibodies from HCV+/LKM1+ patients immunoprecipitated either NS3, NS5a, or both, and these reactivities were specifically inhibited by immobilized CYP2D6. In conclusion, HCV+/LKM1+ sera recognize a specific conformational epitope on CYP2D6 between amino acids 254 to 288, the region that contains the major linear epitope in type 2 autoimmune hepatitis patients. Cross-reactivity due to molecular mimicry at the B-cell level was shown between the CYP2D6 and the HCV NS3 and NS5a proteins and could explain the presence of anti-LKM1 in patients chronically infected with HCV. Further investigation of the role played by this molecular mimicry in HCV-infected patients may lead to more specific strategies for diagnosis and treatment.

Cytochrome P4502D6(193-212): a new immunodominant epitope and target of virus/self cross-reactivity in liver kidney microsomal autoantibody type 1-positive liver disease

Cytochrome P4502D6 (CYP2D6), target of liver kidney microsomal autoantibody type 1 (LKM1), characterizes autoimmune hepatitis type 2 (AIH2) but is also found in patients with chronic hepatitis C virus (HCV) infection. To provide a complete linear epitope B cell map of CYP2D6, we tested peptides spanning the entire sequence of CYP2D6. In addition to confirming previously described antigenic sites, we identified four new epitopes (193-212, 238-257, 268-287, and 478-497). CYP2D6(193-212) is immunodominant and was the target of 12 of 13 (93%) patients with AIH2 and 5 of 10 (50%) HCV/LKM1-positive patients. Because LKM1 is present in both AIH2 and a viral infection, we tested whether Abs to CYP2D6(193-212) arise through cross-reactive immunity between virus and self. We identified a hexameric sequence "RLLDLA" sharing 5 of 6 aa with "RLLDLS" of HCV(2985-2990) and all 6 aa with CMV(130-135). Of 17 CYP2D6(193-212)-reactive sera, 11 (7 AIH and 4 HCV) reacted by ELISA with the HCV homologue, 8 (5 AIH and 3 HCV) with the CMV homologue, and 8 (5 AIH and 3 HCV) showed double reactivity. Autoantibody binding to CYP2D6(193-212) was inhibited by preincubation with HCV(2977-2996) or CMV(121-140). Recombinant HCV-nonstructural protein 5 and CMV-UL98 proteins also inhibited Ab binding to CYP2D6(193-212). Affinity-purified CYP2D6(193-212)-specific Ab inhibited the metabolic activity of CYP2D6. The demonstrated similarity and cross-reactivity between CYP2D6(193-212) and two unrelated viruses suggests that multiple exposure to viruses mimicking self may represent an important pathway to the development of autoimmunity.

Detection of liver kidney microsomal type 1 antibody using molecularly based immunoassays

AIMS

To assess the diagnostic value of two commercial molecularly based immunoassays detecting liver kidney microsomal type 1 antibody (LKM1).

METHODS

The performance of Varelisa and LKM1 enzyme linked immunosorbent assay (ELISA) was compared with immunofluorescence, and two validated research techniques-an in house ELISA and a radioligand assay measuring antibodies to P4502D6. Thirty serum samples from three patients with autoimmune hepatitis type 2 covering immunofluorescence titres of 1/10 to 1/10 240 and 55 LKM1 negative controls were tested.

RESULTS

All 30 sera that were LKM1 positive by immunofluorescence were positive by the in house ELISA, the radioligand assay, and LKM1-ELISA, and 29 were also positive by Varelisa. None of the 55 sera negative for LKM1 by immunofluorescence was positive by the in house ELISA and radioligand assay, but one was positive by Varelisa and 14 were positive using the LKM1-ELISA. Agreement between immunofluorescence, the in house ELISA, the radioligand assay, and Varelisa was high (kappa > 0.8), and agreement between immunofluorescence and LKM1-ELISA was moderate (kappa = 0.63).

CONCLUSION

The assay kit marketed as Varelisa allows accurate detection of LKM1.

[Interferon-alpha and auto-immunity]

PURPOSE

To assess the role of endogenous interferon alpha (IFN) in auto-immune experimental models and human diseases, and to evaluate its iatrogenic potential as a therapeutic agent.

MAIN POINTS

IFN is a cytokine involved in cellular immunity, that promotes both differentiation of dendritic cells and the TH1 pathway. Auto-immune side-effects of recombinant IFN depend on IFN dosage and the pathology concerned. The spectrum extends from occurrence of auto-antibodies in an asymptomatic patient to overt disease such as systemic lupus. Antigenic targets of auto-antibodies are diverse: blood cells coagulation factors, immunoglobulin, hormones, intrinsic factor, intracellular components. Thyroiditis is the most frequently reported auto-immune disease occurring during IFN treatment, including hypothyroidism, hyperthyroidism or a bi-phasic pattern. Currently, true incidence of thyroiditis remains debated. It appears very low (under 1%) in hepatologic series using low-dose IFN. The fact that auto-immunity may be related to the treated disease--before use of IFN--must also be addressed: e.g. antinuclear factors and anti-DNA antibodies in chronic myeloid leukemia or anti-actin and anti-LKM antibodies in chronic C hepatitis.

FUTURE PROSPECTS

Recombinant alpha interferon appears more as a trigger than a de novo inducer of auto-immune disorders. Its use as an immunomodulator agent should be treated with caution.

Anti-CYP2D6 antibodies detected by quantitative radioligand assay and relation to antibodies to liver-specific arginase in patients with autoimmune hepatitis

BACKGROUND

Antibodies to cytochrome P4502D6 (CYP2D6) were measured and their prevalence compared with that of antibodies to liver-specific arginase in patients with autoimmune hepatitis (AIH).

METHODS

Anti-CYP2D6 antibodies were measured by sensitive radioligand assay and enzyme-linked immunosorbent assay (ELISA), and anti-arginase antibodies were measured by ELISA in 132 patients (definite AIH 11, probable AIH 36, hepatitis C 20, hepatitis B 23, other autoimmune diseases 42) and 50 healthy controls.

RESULTS

CYP2D6 index (radioligand assay) was significantly higher in all groups of patients than those in healthy controls. A higher index than the cut-off value (mean+3 S.D. in healthy controls) was found in 36.4%, 44.4%, 25.0%, 17.4% and 28.6% of patients with definite AIH, probable AIH, hepatitis C, hepatitis B and other autoimmune diseases, respectively. CYP2D6 index was not related to serum IgG, anti-nuclear antibody or AIH scores, and was weakly correlated with anti-arginase antibody activity. When CYP2D6 index and anti-arginase antibodies were combined, 55.3% of AIH patients were positive for either one or both antibodies.

CONCLUSIONS

Anti-CYP2D6 antibodies by radioligand assay were frequently present in patients with AIH. Combined tests for anti-CYP2D6 radioligand assay and anti-arginase antibodies resulted in detection of 55% of AIH patients.

Mechanisms of liver injury relevant to pediatric hepatology

Hepatocyte injury and necrosis from many causes may result in pediatric liver disease. Influenced by other cell types in the liver, by its unique vascular arrangements, by lobular zonation, and by contributory effects of sepsis, reactive oxygen species and disordered hepatic architecture, the hepatocyte is prone to injury from exogenous toxins, from inborn errors of metabolism, from hepatotrophic viruses, and from immune mechanisms. Experimental studies on cultured hepatocytes or animal models must be interpreted with caution. Having discussed general concepts, this review describes immune mechanisms of liver injury, as seen in autoimmune hepatitis, hepatitis B and C infection, the anticonvulsant hypersensitivity syndrome, and autoimmune polyendocrinopathy. Of the monogenic disorders causing significant liver injury in childhood, alpha-1 antitrypsin deficiency and Niemann-Pick C disease demonstrate the effect of endoplasmic or endosomal retention of macromolecules. Tyrosinemia illustrates how understanding the biochemical defect leads to understanding cell injury, extrahepatic porphyric effects, oncogenesis, pharmacological intervention, and possible stem cell therapy. Pathogenesis of cirrhosis in galactosemia remains incompletely understood. In hereditary fructose intolerance, phosphate sequestration causes ATP depletion. Recent information about mitochondrial disease, NASH, disorders of glycosylation, Wilson's disease, and the progressive familial intrahepatic cholestases is discussed.

Auto-antibodies in hepatitis C

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