Differentiation of specific DNA binding activity of SLE sera from non-specific binding by an addition of dextran sulfate and calcium chloride to the Farr assay system.

A new method for differentiation of specific DNA-binding by human sera from non-specific binding was evaluated with sera from patients with systemic lupus erythematosus in different stages of the disease. An addition of dextran sulfate or calcium chloride to Farr's radioimmunoassay mixture reduced non-specific binding of thermally denatured [3H]DNA of the patient sera without much effect on the specific binding. The measurement of DNA-binding value by the sera in these addition systems provides accurate information with regard to the pathophysiological state of the disease.