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Primary biliary cirrhosis (PBC) and autoimmune cholangitis (AIC) are serologic expressions of an autoimmune liver disease affecting biliary ductular cells. Previously we screened a phage-displayed random peptide library with polyclonal IgG from 2 Australian patients with PBC and derived peptides that identified a single conformational (discontinuous) epitope in the inner lipoyl domain of the E2 subunit of the pyruvate dehydrogenase complex (PDC-E2), the characteristic autoantigen in PBC. Here we have used phage display to investigate the reactivity of PBC sera from 2 ethnically and geographically distinct populations, Japanese and Australian, and the 2 serologic expressions, PBC and AIC. Random 7-mer and 12-mer peptide libraries were biopanned with IgG from 3 Japanese patients with PBC and 3 with AIC who did not have anti-PDC-E2. The phage clones (phagotopes) obtained were tested by capture enzyme-linked immunosorbent assay (ELISA) for reactivity with affinity-purified anti-PDC-E2, and compared with those obtained from Australian patients with PBC. Peptide sequences of the derived phagotopes and sequences derived by biopanning with irrelevant antisera were aligned to develop a guide tree based on physicochemical similarity. Both Australian and Japanese PBC-derived phagotopes were distributed in branches of the guide tree that contained the peptide sequences MH and FV previously identified as part of an immunodominant conformational epitope of PDC-E2, indicating that epitope selection was not influenced by the racial origin of the PBC sera. Biopanning with either PBC or AIC-derived IgG yielded phagotopes that reacted with anti-PDC-E2 by capture ELISA, further establishing that there is a similar autoimmune targeting in PBC and AIC.

Sera from 120 patients with suspected autoimmune rheumatic disease and antinuclear antibodies of anti-SS-B/La specificity were examined by Western blotting for reactivity with the SS-B/La polypeptide of HeLa cells and recombinant SS-B/La derived from a 1.4 kilobase (kb) cDNA encoding approximately 90% of the SS-B/La molecule. All sera reacted with the HeLa cell and the recombinant SS-B/La. One hundred and fourteen (95%) reacted with a set of three Staph. aureus V8 protease-resistant peptides of Mr 30,000, 29,00 and 28,000 from a methionine-rich region of HeLa cell SS-B/La designated the X domain, and 98 (82%) reacted with another set of two protease-resistant peptides of Mr 24,000 and 23,000 from a phosphorylated region of HeLa cell La designated the Y domain. One reacted weakly with the Y domain only. All sera that reacted with X and Y reacted more strongly with X, suggesting that X was the major epitope. Antibodies affinity purified from the X domain reacted strongly with the X peptides but not with the Y peptides and conversely, antibodies affinity purified from the Y domain reacted with the Y peptides but not with the X peptides. Both antibodies reacted with a fusion protein comprising 102 amino acids at the carboxyl terminus of the SS-B/La molecule. This protein contained no methionine, demonstrating that methionines were not involved in the antibody-binding site. Over 80% of patients whose only criteria for selection was the presence of anti-SS-B/La had the clinical, histologic, serologic and phenotypic features of Sjögren's syndrome whilst the remaining 20% had at least two of the features.(ABSTRACT TRUNCATED AT 250 WORDS)

A solid phase radioimmunoassay is described for the detection of autoantibodies to the saline-soluble extractable nuclear antigens, ribonucleoprotein (RNP) and SS-B (or La). This assay depends on enrichment of antigens from a crude, commercially available (Pel Freez, U.S.A.) extract of rabbit thymus by absorption to the F(ab)2 fraction of specific high titre antibody attached to a microtitre plate. Serum antibody reactive with this antigen is then detected by 125I-labelled Protein A. The assay is simple and is more sensitive than the gel diffusion assays in general use for detecting such antibodies.

A population study on pancreatic islet cell antibodies (pica) among 3766 people from the town of Busselton, Western Australia showed that such antibodies were infrequent, the 'classical' insulin-dependent diabetes associated islet cell antibody being present in less than 0.01%. Pancreatic islet cell antibodies in this population were not associated with insulin-dependent diabetes mellitus, and ten known insulin-dependent diabetics did not have these antibodies. These results for an unselected population are in sharp contrast with those derived from studies on highly selected hospital patients.