Specificity of anti-DNA antibodies in SLE--II. Relative contribution of backbone, secondary structure and nucleotide sequence to DNA binding.

Fine specificity of a population of anti-DNA antibodies which bound both ssDNA and dsDNA with apparently equal affinity was studied in two SLE plasma. Sensitivity of DNA binding to increasing sodium chloride concentration indicated that electrostatic interactions occurred between antibody and phosphate moieties of DNA. Secondary nucleic acid structure was important to DNA binding as double-stranded synthetic deoxynucleotide polymers were more effective inhibitors than their substituent single-stranded polymers. Nucleotide bases were also found to play a role in recognition of DNA by these cross-reactive antibodies, as ssDNA binding was sensitive to increasing temperature which caused unstacking of the nucleotide bases. Differing patterns of reactivity with synthetic deoxynucleotide polymers with similar secondary structures but different nucleotide compositions further indicated the importance of nucleotide bases to dsDNA binding by cross-reactive anti-DNA antibodies in SLE plasma.