Anti-nuclear antibodies (ANA) are a group of antibodies directed against various nuclear and some cytoplasmic antigens. Serological tests for ANA play an important role towards the diagnosis of various autoimmune connective tissue disorders. Although these antibodies were first associated with systemic lupus erythematosus (SLE), the list of implicated diseases has expanded and many rheumatic diseases are characterized by the presence of one or more of these ANAs. For instance, anti-SSA/Ro and anti-SSB/La antibodies are associated with SLE and Sjogren's Syndrome (SS), anti-dsDNA and anti-Sm antibodies with SLE, anti-RNP antibodies with mixed connective tissue disease (MCTD) and SLE, anti-Scl-70 antibodies with scleroderma (progressive systemic sclerosis (PSSJ), anti-Jo1 with polymyositis and dermatomyositis and anti-centromere antibodies with CREST syndrome. As ANA ELISA test collectively detects, in one well, total ANAs against double stranded DNA (dsDNA), Sm, U1-RNP (68K), SS-A/Ro, SS-B/La, Scl-70, Jo-1, and centromeric antigens, along with sera positive for IFA HEp-2 ANAs, it is not specific indicators of a connective tissue disease. To monitor more specific antibodies, eight different antigens (dsDNA, SmD1, U1-RNA (68K), SS-A/Ro, SS-B/La, Scl-70, Jo-1, and CENP-B) are coated to different wells in a column or strip for the ELISA screen test of eight different autoimmune antibodies once.
List of Applicable ANAs
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.