Anti-IgE autoantibodies mistaken for specific IgG

During isolation of specific IgE by affinity chromatography, we obtained IgG acting as "specific IgG" in dot immunoassay and RAST. Further analysis of this fraction revealed that this specific IgG was indeed an immune complex consisting of IgG anti-IgE autoantibodies and specific IgE that falsely appeared as specific IgG in the immunoassays. After disruption of complexes, more IgE became accessible, resulting in increased counts per minute in the RAST. Thus, anti-IgE autoantibodies may hinder determination of specific IgE in in vitro immunoassays, since they hide specific IgE immunologically. To demonstrate the isotope specificity of such immune complex-derived IgG, the purified anti-IgE autoantibodies were radiolabeled and used as detection antibodies in immunoblotting. These autoantibodies recognized different IgE preparations, including a recombinant IgE peptide.