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 critica l in deciphering mechanisms of autoimmune pathogenesis. Previous studies id entified a subpopulation of murine lupus monoclonal autoantibodies that exh ibited dual specificity (anti-DNA and anti-IgG2a hinge) and formed stable i mmune complexes [J. Mol. Rec. 10(1997)225]. Two monoclonal autoantibodies, BV 17-45 and BV 16-13, were extensively studied because of their dual speci ficity. To quantitatively assess the role of each specificity in the format ion 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 characterizi ng BV 17-45 showed that the affinity for dsDNA directly correlated with inc reased dsDNA size. Results with BV 16-13 revealed a generally lower affinit y for the various dsDNA fragments. Binding inhibition studies, using a cova lently linked dimer of a nine amino acid synthetic hinge peptide as an inhi bitor of the antibody-43 bp dsDNA interaction, yielded relative affinities for the anti-hinge activity. Binding affinities for the synthetic hinge spe cificity were lower than affinities measured for the anti-dsDNA activity. C ollectively, the binding and inhibition studies provided insight into the c orrelation between dual specificity and avid immune complex formation. A mo del was proposed based on the concept that large dsDNA fragments caused loc alization of the dual-specific antibodies through the anti-dsDNA activity, thereby facilitating subsequent binding and cross-linkage via the anti-hing e specificity. These synergistic interactions resulted in the formation of avid immune complexes. (C) 2001 Elsevier Science Ltd. All rights reserved.