The influence of DNA size on the binding of anti-DNA antibodies in the solid and fluid phase.

To elucidate the interaction of anti-DNA antibodies with DNA, the reactivity of lupus sera with single-stranded fragments from calf thymus, Escherichia coli, and salmon testes DNA was investigated. These fragments were generated by digestion with the restriction enzyme HinfI and ranged in size from approximately 100-4000 bases. By ELISA using polystyrene microtiter plates, fragments from all three species were weakly antigenic compared to intact DNA. These fragments, however, were all antigenic when tested as inhibitors in competition-binding assays. The weak antigenicity of fragments could not be explained by poor adherence to the plates since fragments and intact DNA showed similar levels of binding as assessed using biotinylated preparations. Together, these results demonstrate that the antigenicity of DNA fragments is dramatically altered by solid-phase binding and suggest that constraints on topological or conformational rearrangements of DNA in the solid phase limit antibody interaction.