title: The human biliary epithelial cell plasma membrane antigen in primary biliary cirrhosis: pyruvate dehydrogenase X?
abstract: OBJECTIVE
  Patients with primary biliary cirrhosis (PBC) have autoantibodies that react with components of mitochondrial multienzyme complexes. In addition to binding to mitochondria, patients' autoantibodies to the assumed major autoantigen pyruvate dehydrogenase complex (PDC) dihydrolipoamide acetyltransferase (E2) bind to the plasma membrane of biliary epithelial cells (BECs) specifically in PBC. The aim of this study was to characterize BEC plasma membrane antigens recognized by patients' autoantibodies in PBC.
  
  
  METHODS
  Antigens prepared from intracellular and plasma membrane-enriched fractions of BECs purified from PBC and control liver were immunoblotted with anti-PDC.
  
  
  RESULTS
  In the intracellular fraction, anti-PDC recognized BEC protein bands corresponding to the molecular weight value of E2 and X components of human heart PDC on Western blots. No difference was observed between PDC-E2 in BECs from PBC and controls. However, in PBC but not controls, a 50-kilodalton antigen was detected in the plasma membrane-enriched fraction. This antigen comigrated with component X of purified human heart PDC and was recognized by antibodies specific for PDC-X.
  
  
  CONCLUSIONS
  The data suggest that PDC-X or a cross-reactive 50-kilodalton antigen is the BEC plasma membrane antigen recognized by patients' autoantibodies in PBC. Furthermore, this antigen, rather than PDC-E2, may be a major B-cell target antigen in PBC.
authors.affiliation: University Hospital, and Department of Medicine, University of Birmingham, England. R.E.joplin@bham.ac.uk
authors.forename: R E
authors.initials: RE
authors.lastname: Joplin
authors.forename: L L
authors.initials: LL
authors.lastname: Wallace
authors.forename: J G
authors.initials: JG
authors.lastname: Lindsay
authors.forename: J M
authors.initials: JM
authors.lastname: Palmer
authors.forename: S J
authors.initials: SJ
authors.lastname: Yeaman
authors.forename: J M
authors.initials: JM
authors.lastname: Neuberger
mesh_terms: D000818:Animals; D001324:Autoantigens / Q000032:analysis*; D002462:Cell Membrane / Q000276:immunology; D003593:Cytoplasm / Q000276:immunology; D004847:Epithelial Cells / Q000276:immunology; D006801:Humans; D008105:Liver Cirrhosis, Biliary / Q000276:immunology*; D011768:Pyruvate Dehydrogenase Complex / Q000276:immunology*; D011817:Rabbits
chemical_list: D001324:Autoantigens; D011768:Pyruvate Dehydrogenase Complex