The presence of antibodies against the SSB (also known as La) antigen has been advocated as a diagnostic marker for Sjogren's syndrome (SS), an autoimmune disease characterized by inflammation of the glands leading to diminished or absent glandular secretion. SS may present as a primary disease or associate with other systemic autoimmune diseases as secondary SS. The SSB antigen is a 47 kD ribonucleic protein associated with a spectrum of small RNAs and primarily resides in the nucleus. Antibodies to the SSB antigen appear in more than 80% of patients with primary or secondary SS. Anti-SSB antibodies usually co-present with anti-SSA antibodies, however due to more common of anti-SSA antibodies in other rheumatological conditions such as systemic lupus erythematosis (SLE) and mixed connective tissue disease (MCTD). It suggests that anti-SSB is more specific for primary and secondary SS than anti-SSA.
Autoimmune ELISA kits measure autoimmune antibodies in the serum. It is based on the principle of a solid phase enzyme-linked immunosorbent assay. The assay utilizes a specific antigen for immobilization on the microtiter wells and anti-human IgG antibody conjugated to horseradish peroxidase (HRP) for detection. The test sample is allowed to react simultaneously with the two components, resulting in autoimmune antibodies being sandwiched between the solid phase and enzyme-linked antibodies. After incubation, the wells are washed to remove unbound-labeled antibodies. A HRP substrate, TMB, is added to result in the development of a blue color. The color development is then stopped with the addition of Stop Solution changing the color to yellow. The concentration of autoimmune antibodies is directly proportional to the color intensity of the test sample. Absorbance is measured spectrophotometrically at 450 nm.