Substrate competition between DNase I and anti-DNA antibody

Sera from rabbits immunized with DNA and patients known to have SLE were shown to inhibit the digestion of ¹²⁵I-labeled ss-DNA by pancreatic DNase I. Similarly, DNase present in the serum of a patient with SLE was found to digest the radio-labeled DNA at one-sixth the rate of an equal quantity of DNase present in NHS. The inhibition was shown to be due to isolated anti-DNA antibody in both the immunized rabbit sera and the SLE sera. The type of inhibition involved was demonstrated to be of the competitive variety in which the binding of antibody to DNA presumably blocks enzyme access to the substrate. The possible pathogenetic implications of these findings are discussed.