title: Demonstration of PDC-E1 subunits as major antigens in the complement-fixing fraction M4 and re-evaluation of PDC-E1-specific antibodies in PBC patients.
abstract: BACKGROUND
  Primary biliary cirrhosis (PBC) is characterized by the presence of antimitochondrial antibodies (AMA). Autoantibodies specific for the mitochondrial M4 antigen can be detected by a complement fixation test (CFT) but not by immunoblotting. The aim of this study was to elucidate the identity of the M4 antigen.
  
  
  METHODS
  M4 proteins were purified by affinity chromatography using IgG fractions of PBC marker sera being CFT positive (n=5) or negative (n=5) and identified by Western blotting, silver staining and sequence analysis. Further, a cohort of 57 PBC patients was tested for the reactivity to M4 and pyruvate dehydrogenase complex (PDC).
  
  
  RESULTS
  Two AMA patterns of the marker sera were visualized: CFT-positive sera were defined as PDC-E2(+)/E1(+) and the CFT-negative sera as PDC-E2(+)/E1(-). The major proteins in the M4 fraction could be related to the PDC-E1 subunits. A clear-cut association between anti-M4 reactivity in the CFT and the reactivity to both PDC subunits could also be documented in the cohort of 57 PBC patients showing anti-PDC-E1alpha and E1beta antibodies at a frequency of 74% and 67%.
  
  
  CONCLUSIONS
  CFT reactivity against M4 antigens could be preferentially identified as a reaction against PDC-E1. As PDC-E1 subunits as compared with PDC-E2 lack lipoyl-binding sites, they probably have to be considered as an independent and important target.
authors.affiliation: Department of Internal Medicine I, Medical Clinic, University of Tübingen, Tübingen, Germany. peter.a.berg@uni-tuebingen.de
authors.forename: Christoph P
authors.initials: CP
authors.lastname: Berg
authors.forename: Gerburg M
authors.initials: GM
authors.lastname: Stein
authors.forename: Reinhild
authors.initials: R
authors.lastname: Klein
authors.forename: Maria
authors.initials: M
authors.lastname: Pascu
authors.forename: Thomas
authors.initials: T
authors.lastname: Berg
authors.forename: Winfried
authors.initials: W
authors.lastname: Kammer
authors.forename: Martin
authors.initials: M
authors.lastname: Priemer
authors.forename: Alfred
authors.initials: A
authors.lastname: Nordheim
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: Michael
authors.initials: M
authors.lastname: Gregor
authors.forename: Sebastian
authors.initials: S
authors.lastname: Wesselborg
authors.forename: Peter A
authors.initials: PA
authors.lastname: Berg
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001323:Autoantibodies / Q000097:blood / Q000276:immunology; D001324:Autoantigens / Q000276:immunology*; D015331:Cohort Studies; D003168:Complement Fixation Tests; D005260:Female; D006801:Humans; D016056:Immunodominant Epitopes / Q000276:immunology; D008105:Liver Cirrhosis, Biliary / Q000097:blood / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D008928:Mitochondria / Q000276:immunology; D030481:Pyruvate Dehydrogenase (Lipoamide) / Q000276:immunology*; D011768:Pyruvate Dehydrogenase Complex / Q000276:immunology; D051381:Rats
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D016056:Immunodominant Epitopes; D011768:Pyruvate Dehydrogenase Complex; D030481:Pyruvate Dehydrogenase (Lipoamide)