Analysis of the Mechanisms of Anti-DNA Antibody Binding to DNA

Abstract

Antibodies to DNA (anti-DNA) are a canonical marker for systemic lupus erythematosus (SLE), a prototypic autoimmune disease that is most common in young women and has highly variable immunological and clinical manifestations. Anti-DNA antibodies play a key role in the pathogenesis of lupus as they can form pathogenic immune complexes that can ultimately lead to organ damage. Prior studies showed that the antibody’s charge may influence the formation of immune complexes; DNA is negatively charged because of the phosphodiester backbone and anti-DNA antibodies are rich in positively charged amino acids. To elucidate the mechanisms of anti-DNA antibodies, we wanted to further explore how charge affects antibody binding using as a model a monoclonal antibody. In this study, we tested whether the binding properties of Val-1205, an E310 monoclonal antibody (MAb), are mediated by electrostatic interactions, similar to those identified for serum as well as monoclonal anti-DNA antibodies. For this purpose, we took advantage of this monoclonal antibody that has been re-engineered to express more charge and higher binding avidity to determine how charge affects the association and dissociation of ICs. Enzyme-linked immunosorbent assays (ELISAs) were performed under distinct experimental environments to identify possible changes in antigen-antibody (Ag-Ab) interactions. We found that Val-1205 binds well to DNA in ELISAs and that changing buffer composition without altering pH did not significantly change binding activity. In addition, Val-1205 binding was unchanged by the number of times the antibody had been thawed. However, Val-1205’s binding activity was influenced by salt concentration. When compared to antibodies from SLE patient serum, the Val-1205 antibody had comparable dependence on ionic strength. These results are important since they demonstrate the exquisite dependence on the ionic strength of anti-DNA, reflecting the role of electrostatic interactions. Results presented herein provide new understandings of the mechanism of anti-DNA–DNA interaction and indicate that Val-1205 may be especially dependent on charge-charge interaction. These results also provide an important insight that Val-1205, despite its strong binding affinity, may represent anti-DNA antibodies that are primarily dependent on charge. The dependence on ionic interactions in Val-1205 may be utilized as steppingstones to better understand the immunopathogenesis of lupus.