INHIBITION OF PDC-E2 HUMAN COMBINATORIAL AUTOANTIBODIES BY PEPTIDE MIMOTOPES

Immunohistochemical studies have shown that a unique immunoreactive mo lecule is present near the apical region of human biliary epithelial ( BE) cells in patients with primary biliary cirrhosis (PBC). This can b e visualized by confocal microscopy in PBC livers using a number of un ique monoclonal antibodies to the E2 component of pyruvate dehydrogena se complex (PDC-E2), the autoantigen most commonly recognized by antim itochondrial antibodies (AMA). One such antibody, the murine mAb C355. 1 was used to identify peptide mimotopes of PDC-E2 by screening a rand om dodecapeptide phage library ON 159.2 to identify the possible bioch emical nature of this apical staining molecule. Out of 36 independent clones, 29 showed a common sequence and seven other sequences were sin gly represented. Three common amino acid motifs (SYP, TYVS and VRH) we re found among these eight sequences. Similar to C355.1, the human com binatorial antibodies derived from a patient with PBC, SP1 and SP4, re cognize the inner lipoyl domain of PDC-E2. However, when these antibod ies are used to stain PBC BE cells, SP4 stains the apical region of PB C BE cells with high intensity whereas SP1 produces only cytoplasmic s taining. Competitive inhibition of immunohistochemical staining using PDC-E2 specific human combinatorial antibodies SP1 and SP4 was perform ed 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 pept ide (WMSYPDRTLRTS) stained BE cells from patients with PBC with a high er intensity than controls. Comparable data was obtained with immunoel ectronmicroscopy. These data suggest that a molecular mimic of PDC-E2 is present at the external aspect of PBC BE cells. (C) 1996 Academic P ress Limited