Description
Type: EliA SmDP
Unit Size: -
Test Principle The EliA Sm Wells are coated with native Sm proteins purified from bovine tissue, EliA SmDP Wells are coated with a synthetic SmD3 peptide. If present in the patient's specimen, antibodies to Sm, for EliA SmDP antibodies to the SmD3 peptide, bind to their specific antigen. After washing away non-bound antibodies, enzyme-labeled antibodies against human IgG antibodies (EliA IgG Conjugate) are added to form an antibody-conjugate complex. After incubation, non-bound conjugate is washed away and the bound complex is incubated with a Development Solution. After stopping the reaction, the fluorescence in the reaction mixture is measured. The higher the response value, the more specific IgG is present in the specimen. To evaluate test results, the response for patient samples is compared directly to the response for calibrators. Antigens In their natural state, the small nuclear RNAs, also called U-RNAs (for “uracil rich RNAs”), exist as ribonucleoprotein particles (snRNP). The U snRNP U1, U2, U4, U5 and U6 all contain a group of proteins, the so-called Sm peptides, with the major targets being the B and D polypeptides. Because of cross-reactivity between the A, the C and the B/B' proteins, up to 60% of anti-U1 RNP sera may react with B/B'. Thus, only the presence of anti-D and/or the absence of anti-A and anti-C can be regarded as characteristic for an anti-Sm sera. Until now, all trials to produce an antigenic recombinant SmD protein with a good reactivity failed because of its very special structure. In 2004, an ELISA using a dimethylated SmD peptide was developed which showed to have a significantly higher specificity than traditional assays with purified SmD. The EliA SmDP assay as well as the Varelisa Sm Antibodies assay are coated with a synthetic SmD_3peptide. The EliA Sm Well is coated with a purified Sm antigen. Disease association, antibody prevalence and specificity Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by chronic inflammation of the connective tissue, affecting about 0.5% of the population worldwide. Sm antibodies are found in 5-30% of patients with SLE, depending on the ethnicity of the SLE population. Because of their high disease specificity Sm antibodies have been included in the American College of Rheumatology (ACR) criteria for classification of SLE. Anti-Sm positive sera are almost always also positive for anti-RNP. Anti-Sm reactivity is not described definitely in other diseases, although a few studies describe Sm antibodies in monoclonal gammopathies, schizophrenia and uveitis. Disease activity Numerous studies suggest the association of anti-Sm antibodies with disease activity and particular disease manifestations. When is the measurement recommended? Suspicion of SLE. Antibody isotype IgG Other detection methods IIF on HEp-2 (punctate staining pattern throughout the nucleus; only the nucleolar regions are generally unstained). The immunofluorescence technique cannot distinguish between anti-U1 snRNP and anti-Sm antibodies. Other methods (e.g. counterimmunoelectrophoresis, immunoprecipitation; immunoblotting) can be used but are not necessarily useful for routine.
