Stability of DNA/Anti-DNA Complexes

Antigenic specificity, concentration in serum, and binding avidity of different types of antibodies to DNA all contribute to the nature of circulating DNA/anti-DNA complexes in systemic lupus erythematosus (SLE), and thereby influence the potential of such complexes for tissue injury in this disorder. With highly purified single(s) and double(d) stranded 3 H-DNA prepared from Escherichia coli , the rate of dissociation of DNA/anti-DNA complexes in the presence of excess unlabeled DNA was studied as a function of temperature and DNA conformation. At cold temperatures dissociation of complexes of antibody and ssDNA or dsDNA was slow and did not reach equilibrium. At 37°C “off rates” for ssDNA/antibody complexes generally were rapid, dissociation being complete within 1 hr. dsDNA/antibody complexes, on the other hand, were much more stable at higher temperatures than those formed with ssDNA. With many SLE sera, the majority of dsDNA remained bound to antibody after 24 hr of incubation with a large excess of unlabeled DNA. Kinetic studies of this type were compared with binding isotherms as methods of obtaining information concerning binding avidities of antibody for dsDNA and ssDNA. The implications of these findings are discussed with regard to i) the pathogenicity of dsDNA/anti-DNA complexes, and ii) the difficulty of estimating binding avidity in multivalent antigen, antibody systems.