High avidity anti-dsDNA IgG antibodies are believed to play an important role in the pathogenesis of the autoimmune disease systemic lupus erythematosus (SLE) and therefore attempts have been made to reduce the concentration of these antibodies in the bloodstream of SLE patients. Previously we reported the development of an antigen based heteropolymer (AHP), a bispecific complex prepared by using the avidin-biotin system to crosslink dsDNA to a mAb specific for the human erythrocyte (E) complement receptor. Our studies indicated that this AHP could bind anti-dsDNA antibodies to E and facilitate clearance of these autoantibodies from the circulation of a monkey without E destruction. Here we report an improved covalent crosslinking procedure and purification scheme in which the AHP construct is isolated by precipitation in 50% saturated ammonium sulfate. We used a dsDNA binding dye, PicoGreen, to demonstrate specificity of binding of dsDNA to E via the AHP. The efficacy of the AHP in binding IgG anti-dsDNA antibodies to E was demonstrated in a sensitive and quantitative assay, based on the time resolved fluorescence properties of europium-labeled anti-human IgG mAbs used to probe the E. We also used this assay to screen SLE patient and normal plasmas for levels of anti-dsDNA IgG. The results of this assay correlate very well with the Farr assay, and therefore this approach may be useful in the development of informative and specific assays for a variety of autoantibodies. Treatment of SLE plasmas with E-AHP under conditions close to physiological led to substantial reductions (> or = 90%) in anti-dsDNA titers. It should be possible to test these new AHP for their ability to target and safely remove IgG anti-dsDNA antibodies from the circulation in animal models.