Interaction of dual-specific autoantibodies with dsDNA and a synthetic dimer peptide simulating the hinge region of IgG2a molecules

Anti-dsDNA autoantibodies and immune complex formation are major factors in SLE pathogenesis. Understanding stable immune complex formation is critical in deciphering mechanisms of autoimmune pathogenesis. Previous studies identified a subpopulation of murine lupus monoclonal autoantibodies that exhibited dual specificity (anti-DNA and anti-IgG2a hinge) and formed stable immune complexes [J. Mol. Rec. 10(1997)225]. Two monoclonal autoantibodies, BV 17–45 and BV 16–13, were extensively studied because of their dual specificity. To quantitatively assess the role of each specificity in the formation of stable immune complexes, studies were performed to determine binding affinities for various sized dsDNA fragments (21, 43, 84, and 114 bp) and the covalent dimer of a nine amino acid hinge peptide. Results characterizing BV 17–45 showed that the affinity for dsDNA directly correlated with increased dsDNA size. Results with BV 16–13 revealed a generally lower affinity for the various dsDNA fragments. Binding inhibition studies, using a covalently linked dimer of a nine amino acid synthetic hinge peptide as an inhibitor of the antibody–43 bp dsDNA interaction, yielded relative affinities for the anti-hinge activity. Binding affinities for the synthetic hinge specificity were lower than affinities measured for the anti-dsDNA activity. Collectively, the binding and inhibition studies provided insight into the correlation between dual specificity and avid immune complex formation. A model was proposed based on the concept that large dsDNA fragments caused localization of the dual-specific antibodies through the anti-dsDNA activity, thereby facilitating subsequent binding and cross-linkage via the anti-hinge specificity. These synergistic interactions resulted in the formation of avid immune complexes.