DNA binding activity ofserum frompatients withsystemic lupus erythematosus

SUMMARY Thereaction conditions essential forreproducible useofthecellulose ester membrane filter assay foranti-DNA antibody levels inpatients withsystemic lupus erythematosus aredescribed. A dependence ofDNA-binding capacity onserum concentration wasobserved intheassay, requiringthatserumconcentrations becomparable indeterminations ofDNA-binding activity of different sera andwhencomparing different published studies. TheDNA-binding capacity of serum fromlupus patients wasfound tobesignificantly different from that ofhealthy controls. However, thebinding capacities were notsignificantly different between lupus patients with andwithout nephritis. Therelative avidity oftheanti-DNA antibodies wereestimated fromplots of1/DNA boundvs1/DNAfree andthese data indicate that theavidities oftheantibodies fromthetwo groups oflupus patients arenotsignificantly different. This observation suggests that thetightness ofbinding between theDNA andtheserumanti-DNA antibodies cannot beusedtopredict immunecomplex-induced nephritis inlupus patients.