Utility of a synthetic poly dT band included in a commercial blot assay to detect anti-DNA antibodies.

Systemic lupus erythematosus (SLE) patients exhibit anti-DNA antibodies with a heterogeneous pattern of individual specificity of binding. Likewise, the methods used for the measurement of anti-DNA antibodies exhibit a wide spectrum of binding avidities detection. We have evaluated the clinical utility of a band of synthetic poly dT included as an antigen in a recently commercialized blot system for antinuclear antibodies to detect anti-DNA antibodies. Sera from 45 individuals (36 patients with SLE, 9 without autoimmune disease negative for anti-nDNA by ELISA) were evaluated by the commercial immunoblot assay, ELISA for anti-nDNA, and conventional immunofluorescence using Crithidia lucillae substrate. Kappa statistics were used to determine the agreement between assays. The results obtained show a better agreement between positive bands for poly dT and anti-nDNA antibodies measured by IIF than by ELISA (Kappa index 0.64 vs. 0.44), although there are discrepant results. Likewise, positive bands for poly dT were obtained in patients with active SLE as assessed by decreased serum C3 concentration. We conclude that anti-poly dT reactivity reveals anti-nDNA antibodies of medium-high avidity, which show best disease activity.