title: Inhibition of PDC-E2 human combinatorial autoantibodies by peptide mimotopes.
abstract: Immunohistochemical studies have shown that a unique immunoreactive molecule is present near the apical region of human biliary epithelial (BE) cells in patients with primary biliary cirrhosis (PBC). This can be visualized by confocal microscopy in PBC livers using a number of unique monoclonal antibodies to the E2 component of pyruvate dehydrogenase complex (PDC-E2), the autoantigen most commonly recognized by antimitochondrial antibodies (AMA). One such antibody, the murine mAb C355.1 was used to identify peptide mimotopes of PDC-E2 by screening a random dodecapeptide phage library ON 159.2 to identify the possible biochemical nature of this apical staining molecule. Out of 36 independent clones, 29 showed a common sequence and seven other sequences were singly represented. Three common amino acid motifs (SYP, TYVS and VRH) were found among these eight sequences. Similar to C355.1, the human combinatorial antibodies derived from a patient with PBC, SP1 and SP4, recognize the inner lipoyl domain of PDC-E2. However, when these antibodies are used to stain PBC BE cells, SP4 stains the apical region of PBC BE cells with high intensity whereas SP1 produces only cytoplasmic staining. Competitive inhibition of immunohistochemical staining using PDC-E2 specific human combinatorial antibodies SP1 and SP4 was performed using five of the above dodecapeptides. Interestingly, the peptides selected with C355.1 differentially inhibited the binding of SP1 and SP4 to PBC BE cells. Finally, rabbit sera raised against one such peptide (WMSYPDRTLRTS) stained BE cells from patients with PBC with a higher intensity than controls. Comparable data was obtained with immunoelectronmicroscopy. These data suggest that a molecular mimic of PDC-E2 is present at the external aspect of PBC BE cells.
authors.affiliation: Division of Rheumatology, Allergy and Clinical Immunology, University of California Davis, School of Medicine 95616, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Leung
authors.forename: S
authors.initials: S
authors.lastname: Cha
authors.forename: R E
authors.initials: RE
authors.lastname: Joplin
authors.forename: C
authors.initials: C
authors.lastname: Galperin
authors.forename: J
authors.initials: J
authors.lastname: Van de Water
authors.forename: A A
authors.initials: AA
authors.lastname: Ansari
authors.forename: R L
authors.initials: RL
authors.lastname: Coppel
authors.forename: P J
authors.initials: PJ
authors.lastname: Schatz
authors.forename: S
authors.initials: S
authors.lastname: Cwirla
authors.forename: L E
authors.initials: LE
authors.lastname: Fabris
authors.forename: J M
authors.initials: JM
authors.lastname: Neuberger
authors.forename: M E
authors.initials: ME
authors.lastname: Gershwin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D001324:Autoantigens / Q000737:chemistry; D001659:Biliary Tract / Q000201:enzymology / Q000276:immunology; D004848:Epithelium / Q000201:enzymology / Q000276:immunology; D006801:Humans; D008105:Liver Cirrhosis, Biliary / Q000201:enzymology / Q000276:immunology; D051379:Mice; D018716:Molecular Mimicry; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry / Q000276:immunology; D011768:Pyruvate Dehydrogenase Complex / Q000737:chemistry / Q000276:immunology*; D011817:Rabbits
chemical_list: D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D001324:Autoantigens; D019151:Peptide Library; D010455:Peptides; D011768:Pyruvate Dehydrogenase Complex