Systemic lupus erythematosus (SLE) is a systemic autoimmune disease belonging to the collagenosis group. Diagnosis is based on 11 criteria defined by the American College of Rheumatology (ACR) and modified in 1997. If 4 of 11 criteria are present, the probability of SLE is between 80 and 90%.
Antibodies against dsDNA are the main focus in the serological diagnosis of SLE. These antibodies can be found in 60 to 90% of patients, depending on the activity of the disease. Anti-dsDNA antibodies are in rare cases also found in patients with other autoimmune diseases (e.g. autoimmune hepatitis) or infections as well as in clinically healthy persons. 85% of people in the latter group develop SLE within 5 years of initial detection of anti-dsDNA. However, SLE cannot be excluded if anti-dsDNA antibodies are not detected.
Antibodies against nucleosomes are also an exclusive marker of SLE, provided that they are determined using an advanced test system with a target antigen that is free of histone H1, Scl-70 and other non-histone proteins.
Various test methods are available for the routine detection of autoantibodies against dsDNA: enzyme immunotests (ELISA, EUROASSAY, EUROLINE), Farr RIA and the Crithidia luciliae immunofluorescence test (CLIFT). The various test systems differ, sometimes greatly, in sensitivity and specificity. Conventional CLIFT shows a particularly high disease specificity, while the IIFT Crithidia luciliae sensitive is a very sensitive test.
Using an innovative biological preparation, scientists at EUROIMMUN have developed a new test system: the Anti-dsDNA-NcX ELISA, which surpasses by far the diagnostic quality characteristics of all conventional anti-dsDNA ELISA. The secret of the innovation lies in the use of highly purified nucleosomes as the new linking substance. Since nucleosomes have a strong adhesive ability, even the smallest concentration of these is highly suited to coupling isolated dsDNA to the surface of a microplate well. Poly-L-lysine and protamine sulphate are now obsolete, and many false positive reactions can be avoided. In a clinical comparative study of 378 patients with rheumatic diseases (of these 209 with SLE), the Anti-dsDNA-NcX ELISA yielded an 8% higher sensitivity than the anti-dsDNA RIA (Farr assay), demonstrating its superior capabilities.
Nevertheless, different test methods identify different SLE subgroups. To increase the serological detection rate different test systems should be combined.