Description:

The Diagnostic Automation SSB (La) Enzyme- Linked Immunosorbent Assay (ELISA) is intended for the detection and semi-quantitation of antibodies to SSB (La) in human sera. The assay is to be used to detect antibodies in a single serum specimen. The results of the assay are to be used as an aid to the diagnosis of autoimmune disease.

Systemic autoimmune disease is characterized by the presence of circulating auto antibodies directed to a wide variety of cellular antigens. Systemic lupus erythematosis (SLE) commonly referred to as Lupus is the best known of these diseases. Other possible connective tissue diseases include mixed connective tissue disease (MCTD), Sjogren syndrome, sclerodema, and polymyositis/dermatomyositis. The majority can be diagnosed by clinical presentation and their antibody profiles to the various antigens involved, which include dsDNA, Sm, RNP, SSA (Ro), SSB (La), Scl-70, Jo-1 and Histones. Therefore, immunoassays for auto antibodies are useful for diagnostic and prognostic evaluations of autoimmune disease.

La (also named SSB) antigen consists of protein complexed with RNA. Approximately 60% of patients with Sjogren syndrome and 35% of SLE patients have antibodies to SSB (La). SSA (Ro) antibody occurs in virtually all sera with SSB (La) antibody. However, some SLE patients have Ro only antibody profiles. SLE patients which are Ro positive, SSB (La) negative are more likely to develop nephritis.

Classically, antibodies to autoimmune antigens are detected by double immunodiffusion. However, the test is lengthy and suffers from weak sensitivity. Enzyme-Linked Immunosorbent Assays (ELISAs) combine greater sensitivity with ease of use. Many ELISAs have been developed and validated for detecting auto antibodies to various antigens.

The DAI SSB (La) test is an Enzyme-Linked Immunosorbent Assay to detect IgG, IgA, and IgM antibodies to SSB (La) antigens. Purified SSB (La) antigens are attached to a solid phase microassay well. Enzyme-Linked Immunosorbent Assays (ELISA) relies on the ability of biological materials (i.e., antigens) to adsorb to plastic surfaces such as polystyrene (solid phase). When antigens bound to the solid phase are brought into contact with a patient's serum, antigen specific antibody, if present, will bind to the antigen on the solid phase forming antigen antibody complexes. Excess antibody is removed by washing. This is followed by the addition of goat anti-human IgG, A, M conjugated with horseradish peroxidase which then binds to the antibody-antigen complexes. The excess conjugate is removed by washing, followed by the addition of Chromogen/Substrate, tetramethylbenzidine (TMB). If specific antibody to the antigen is present in the patient's serum, a blue color develops. When the enzymatic reaction is stopped with 1N H2SO4, the contents of the wells turn yellow. The color, which is indicative of the concentration of antibody in the serum, can be read on a suitable spectrophotometer or ELISA microwell plate reader.