title: Apotopes and the biliary specificity of primary biliary cirrhosis.
abstract: Primary biliary cirrhosis (PBC) is characterized by antimitochondrial antibodies (AMAs), directed to the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Notwithstanding the presence of mitochondria in virtually all nucleated cells, the destruction in PBC is limited to small intrahepatic bile ducts. The reasons for this tissue specificity remain unknown, although biliary epithelial cells (BECs) uniquely preserve the PDC-E2 epitope following apoptosis. Notably, PBC recurs in an allogeneic transplanted liver, suggesting generic rather than host PBC-specific susceptibility of BEC. We used cultured human intrahepatic BECs (HIBECs) and other well-characterized cell lines, including, HeLa, CaCo-2 cells, and nontransformed human keratinocytes and bronchial epithelial cells, to determine the integrity and specific localization of PDC-E2 during induced apoptosis. All cell lines, both before and after apoptosis, were tested with sera from patients with PBC (n = 30), other autoimmune liver and rheumatic diseases (n = 20), and healthy individuals (n = 20) as well as with a mouse monoclonal antibody against PDC-E2 and AMA with an immunoglobulin A isotype. PDC-E2 was found to localize unmodified within apoptotic blebs of HIBECs, but not within blebs of various other cell lineages studied. The fact that AMA-containing sera reacted with PDC-E2 on apoptotic BECs without a requirement for permeabilization suggests that the autoantigen is accessible to the immune system during apoptosis.
  
  
  CONCLUSIONS
  Our data indicate that the tissue (cholangiocyte) specificity of the autoimmune injury in PBC is a consequence of the unique characteristics of HIBECs during apoptosis and can be explained by exposure to the immune system of intact immunoreactive PDC-E2 within apoptotic blebs.
authors.affiliation: Division of Rheumatology, University of California at Davis, Davis, CA 95616, USA.
authors.forename: Ana
authors.initials: A
authors.lastname: Lleo
authors.forename: Carlo
authors.initials: C
authors.lastname: Selmi
authors.forename: Pietro
authors.initials: P
authors.lastname: Invernizzi
authors.forename: Mauro
authors.initials: M
authors.lastname: Podda
authors.forename: Ross L
authors.initials: RL
authors.lastname: Coppel
authors.forename: Ian R
authors.initials: IR
authors.lastname: Mackay
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Gores
authors.forename: Aftab A
authors.initials: AA
authors.lastname: Ansari
authors.forename: Judy
authors.initials: J
authors.lastname: Van de Water
authors.forename: M Eric
authors.initials: ME
authors.lastname: Gershwin
mesh_terms: D000906:Antibodies / Q000276:immunology; D000918:Antibody Specificity; D017209:Apoptosis; D001324:Autoantigens / Q000276:immunology / Q000378:metabolism*; D015551:Autoimmunity / Q000276:immunology; D001653:Bile Ducts, Intrahepatic / Q000378:metabolism / Q000473:pathology*; D018938:Caco-2 Cells; D002460:Cell Line; D002478:Cells, Cultured; D051047:Dihydrolipoyllysine-Residue Acetyltransferase / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology*; D000939:Epitopes / Q000276:immunology / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015603:Keratinocytes; D008105:Liver Cirrhosis, Biliary / Q000209:etiology / Q000378:metabolism / Q000473:pathology*; D008928:Mitochondria / Q000276:immunology; D024101:Mitochondrial Proteins / Q000378:metabolism*
chemical_list: D000906:Antibodies; D001324:Autoantigens; D000939:Epitopes; D024101:Mitochondrial Proteins; C052359:DLAT protein, human; D051047:Dihydrolipoyllysine-Residue Acetyltransferase