Autoimmune diseases are categorized into two general groups: Those producing tissue-specific autoantibodies, the other where antibodies are produced against normal cell nuclear and/or cytoplasmic antigens with no tissue type specificity. The latter includes diseases such as mixed connective tissue disease, scleroderma, rheumatoid arthritis, dermatomyositis, polymyositis, Systemic lupus erythematosus (SLE) and Sjogren syndrome and are collectively know as the Systemic Rheumatoid Diseases (SRD).
Systemic lupus erythematosus (SLE) is a well known chronic inflammatory illness that is characterised by remissions and exacerbations with distinct immunologic abnormalities, most notably, the presence of antinuclear antibodies. Antibodies to native DNA (anti-DNA) are of considerable interest in the diagnosis and management of patients with SLE as they are rarely found in other rheumatic diseases, and variation in levels correlate with disease activity.
Antinuclear antibodies (ANAs) directed against a variety of macromolecules occur in extraordinarily high frequency in systemic rheumatic diseases. The list of implicated diseases has expanded and many characterised by the presence of one or more ANA, e.g. (a) anti-SS-A(Ro) and anti-SS-B(La) antibodies are associated with SLE and Sjogren’s Syndrome (SS), (b) anti-dsDNA and anti-Sm antibodies with SLE, (c) anti-histone antibodies with SLE and Drug Induced Lupus, (d) anti-RNP antibodies with mixed connective tissue disease, (MCTD) and SLE, (e) anti-Scl-70 antibodies with scleroderma, (f) anti-Jo-1 antibodies with polymositis and dermatomyositis and (g) anti-centromere antibodies with CREST syndrome.
IFA and EIAs are widely used in the detection of ANAs. ELISA assays are more often being used to screen patient’s serum for the presence of ANA’s of clinical significance as they lend themselves to automation and objective interpretation. The Farr Assay (RIA) remains tha most sensitive method for detection of dsDNA.