Antibodies against the COOH-terminal region of E-coli ClpP protease in patients with primary biliary cirrhosis

Background/Aims: The presence of antibodies in sera from patients with autoimmune diseases is an important tool for diagnosis and for providing insights into the mechanisms leading to autoimmunity. The aim of this study was to characterize new reactive antigens in liver autoimmune diseases. Methods: Sera of patients with liver-related autoimmune (n=74) and non-liver-related autoimmune (n=211) diseases, non-autoimmune liver diseases (n=18) and healthy controls (n=160) were evaluated for antibodies against E. coli ClpP protease (EClpP) and 20S proteasome by immunoblot analysis. Results: Antibodies against EClpP were detected in 15 of 50 patients with primary biliary cirrhosis, in only one of 100 patients with systemic lupus erythematosus, and in three healthy subjects (Chi-square 59.1, d.f. 2, p< 0.001). Antibodies to 20S proteasome were found in only 35 of 100 patients with systemic lupus erythematosus. All other sera from patients with autoimmune diseases, liver diseases other than primary biliary cirrhosis, and healthy controls were negative for both antigens. Both IgG and IgM classes of antibodies against EClpP were present in primary biliary cirrhosis patient sera with titers of 1/400-1/1000. By using recombinant techniques and peptide ELISA, the immunodominant EClpP epitope recognized by the sera from primary biliary cirrhosis patients was localized in the amino acid sequences 177-194 (QIERDTERDRFLSAPEAV) within the COOH-terminal of EClpP. Affinity-purification of these anti-EClpP antibodies and immunoabsorption experiments established that the antibodies are specific for the bacterial EClpP. Conclusions: Bacterial ECIpP has been identified as a new antigen specifically reacting with sera from approximately one third of patients with primary biliary cirrhosis.