The influence of DNA size on the binding of antibodies to DNA in the sera of normal human subjects and patients with systemic lupus erythematosus (SLE)

To elucidate antibody recognition of DNA in normal and aberrant immunity, t he binding of sera of normal human subjects (NHS) and patients with SLE was tested with mammalian and bacterial DNA varying in size. Klebsiella pneumo niae (KP) and calf thymus (CT) single-stranded DNA (ssDNA) were investigate d as model antigens using the restriction enzyme HinfI to generate fragment s with the size range of 800-5000 base pairs. The influence of size on acti vity was assessed by ELISA by both titration of serum as well as coating an tigen concentration. In both assay formats, SLE sera bound equivalently to intact CT and KP DNA, but had dramatically reduced reactivity to fragments of both antigens. In contrast, NHS bound similarly to intact KP DNA and its fragments but had low reactivity to CT DNA. These results suggest that SLE and NHS anti-DNA react with different antigenic determinants on DNA, as sh own by cross-reactivity as well as size dependency in solid-phase assays.