Direct Binding of Monomeric Anti‐DNA Antibodies to Raji Cells

Abstract

The Raji-cell test is one of the most widely used methods for the detection and quantitation of immune complexes. Immune complexes and not 7S IgG bind via C3 to complement receptors on the cell membrane of the Raji cell. During sucrose gradient fractionation of human and murine systemic lupus erythematosus sera, with a high Raji cell-binding activity, we could not demonstrate immune complexes in these sera. Subsequent analysis showed that the major part of the Raji cell binding was used by 7S IgG with an anti-DNA specificity. Blocking experiments with complement-bearing aggregated IgG revealed that complement and Fc receptors were not involved in the binding of these anti-DNA antibodies to Raji cells. We conclude that the Raji cell test is not suitable for the detection and quantitation of immune complexes in sera containing anti-DNA antibodies.