DNA binding proteins in canine sera. A method for removal of nonspecific DNA binding in the Farr assay.

A panel of canine sera, the majority of which were collected from clinically healthy dogs, were investigated for antibodies against double stranded (dsDNA) by the Farr radioimmunoassay technique. Non-specific DNA binding agents interfering with the Farr assay were detected in all sera. Heat inactivation at 60 degrees C or treatment with dextran sulphate was shown to eliminate this kind of unspecific DNA binding while not affecting true antibodies to dsDNA. Canine sera positive in the Farr assay after inactivation at 60 degrees C were positive also in immunofluorescence for anti-nuclear antibody on rat liver sections and for dsDNA with Chrithidia luciliae as antigen preparation. IgG or glycoprotein nature of the non-specific DNA binding could be excluded by means of affinity chromatography on protein A and the lectin lentil.