Reactivities to the Sm autoantigenic complex and the synthetic SmD1-aa83-119 peptide in systemic lupus erythematosus and other autoimmune diseases.

The Sm antigenic complex is, besides dsDNA, the most important and specific autoimmune target in systemic lupus erythematosus (SLE). The population of anti-Sm Ab elicited is very heterogeneous in terms of epitope specificity resulting in a strong assay dependent detectability. Based on the description of a new autoantigenic target, the SmD1-aa83-119 peptide, we analysed 50 healthy persons and 205 patients with different autoimmune and other disorders with regard to their anti-Sm reactivities using different assays. The prevalence of anti-SmD1 peptide Ab and anti-Sm Ab in SLE was 36.0 (40/111) and 9.9% (11/111), respectively. The respective values obtained for non-SLE patients were 2.8 (4/144) and 5.3% (5/94). In SLE, anti-SmD1 peptide Ab are positively correlated to disease activity, nephritis and anti-dsDNA Ab. The association between reactivities of SLE samples in the traditional anti-Sm and the anti-SmD1 peptide ELISA was found to be 63.6%, contrasting markedly with the situation in non-SLE patients (no double-positive sera). SLE samples with an anti-Sm response restricted to the SmD1 peptide are completely negative in immunoblot, supporting the conformational nature of this epitope. Positive immunoblot reactions with the SmD1 polypeptide are not inhabitable by the synthetic SmD1-aa83-119 peptide. Comparing anti-Sm reactivities detected by ELISAs with those in immunoblot, different patterns were observed, reflecting the heterogeneous autoimmune response to this antigen. In conclusion, the anti-SmD1-aa83-119 peptide ELISA substantially completes the panel of methods for autoantibody testing. As none of the assays presently available covers the whole spectrum of epitope specificities of anti-Sm Abs elicited in SLE, it does not replace traditional anti-Sm ELISAs.

The antinuclear autoantibodies Sp100 and gp210 persist after orthotopic liver transplantation in patients with primary biliary cirrhosis.

BACKGROUND/AIMS: Primary biliary cirrhosis is an autoimmune liver disease which is characterized by the presence of autoantibodies directed against mitochondrial components which belong to the pyruvate dehydrogenase enzyme complex. Apart from antibodies against mitochondrial components, primary biliary cirrhosis patients often show antibodies against nuclear components, of which anti-Sp100 and anti-gp210 are considered to be disease specific. We investigated the incidence and course of antibodies against nuclear components in primary biliary cirrhosis patients before and after liver transplantation. METHODS: Sera from 42 primary biliary cirrhosis patients were studied using indirect immunofluorescence to detect antibodies against mitochondrial components and antibodies against nuclear components, ELISA to detect anti-Sp100, and immunoblot analysis to detect anti-gp210 and antibodies against nuclear components subtypes. RESULTS: Ninety-three percent of primary biliary cirrhosis patients in our study were antimitochondrial antibody positive. Forty-three percent of the patients were antinuclear antibody positive. Of these, 35% had antibodies against Sp100 and 36% were positive for anti-gp210. After transplantation, antimitochondrial antibody titers as well as antinuclear antibody titers decreased in all patients. Autoantibodies in low titer persisted for up to 13 years. The pattern of nuclear autoantigens recognized by patient sera was unchanged after liver transplantation. However, the antinuclear antibody pattern was very different between the individual patients. Anti-Sp100 and anti-gp210 were not detected in sera of patients with autoimmune hepatitis, hepatitis C infection, inflammatory bowel disease, connective tissue diseases, or primary sclerosing cholangitis. The serum alkaline phosphatase level was not different in antinuclear antibody negative or positive patients before or after transplantation. CONCLUSIONS: We conclude that the persistence of antibodies against mitochondrial components, and anti-Sp100 and anti-gp210 in primary biliary cirrhosis patients after liver transplantation is disease specific, but that this does not reflect recurrent disease activity in the graft.