The role of the nitric oxide(NO) radicalin systemic lupus erythematosus(SLE) pathogenesishas been investigated in the present study. The binding characteristics of SLE autoantibodies with native calf thymus DNA, native and NO-modified plasmid DNA were assessed. Binding characteristics and specificity of antibodies were analysed by direct binding and inhibition ELISA, gel retardation assay and quantitativeprecipitin titration.The data shows preferentialbinding of SLE autoantibodiesto NO-modified plasmid DNA (NO-DNA) in comparison with native plasmid DNA. Inhibition ELISA reiterates the direct binding results. Gel retardation assay further substantiated the enhanced recognition of NO-DNA by anti-DNA autoantibodies. The binding affinity of modified and native plasmid DNA with one of the SLE IgGs was calculated, using the Langmuir plot. The apparent association constant for NO-plasmid DNA was found to be highest, followed by native calf thymus DNA and native plasmid DNA. The results suggest that the NO radical modification of plasmid DNA causes perturbations, resulting in the generation of neo-epitopes, and making it a potential immunogen. The DNA modified with the NO radical may be one of the factors for the induction of circulating SLE anti-DNA autoantibodies.
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