Anti-nuclear antibodies (ANA) are a group of antibodies directed against various nuclear and some cytoplasmic antigens. 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-histone antibodies with SLE and Drug Induced Lupus, 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. ANA are usually detected by indirect immunofluorescence (IFA) on HEp-2. Because of certain limitations of IFA, ANA ELISA test is more robust offering several advantages including ease of operation and not requiring skills needed to perform and read IFA reactions. ANA ELISA test is able to efficiently screen large numbers of patient samples and reduces human error. As ANA ELISA test collectively detects, in one well, total ANAs against double stranded DNA (dsDNA), Histones, SS-A/Ro, SS-B/La, Sm, Sm/RNP, Scl-70, Jo-1, and centromeric antigens, more specific antibody tests are recommended to perform in patients with positive ANA.
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.