A novel trait of naturally occurring anti-DNA antibodies: dissociation from immune complexes in neutral 0.3-0.5 M NaCl

Monoclonal and polyclonal anti-DNA antibodies from autoimmune mice, and experimentally induced rabbit anti-nucleic acid polyclonal antibodies were tested for stability of binding to nucleic acids in the presence of various concentrations of NaCl by an enzyme-linked immunosorbent assay (ELISA). Murine monoclonal antibodies 2C10 (IgG2b) and 1A2 (IgG2a), which are known to react specifically with double-stranded (ds) DNA, dissociated completely from their complexes with DNA when washed with a neutral 0.5 M NaCl solution. Another monoclonal antibody (MoAb) (IgM,kappa), polyreactive with single-stranded (ss) DNA, cardiolipin, and trinitrophenylhapten (TNP), was also dissociated from its complexes with ss DNA, but not from its complexes with TNP, by 0.3-0.5 M NaCl. Similar differences were observed in the binding stability of serum antibodies from autoimmune mice to DNA and TNP. In contrast, anti-nucleic acid polyclonal antibodies induced in rabbits by immunization with poly(I), poly(dT) or poly(ADP-ribose) were not significantly dissociated from their immune complexes with relevant antigens or DNA by 0.5 M NaCl. The finding that nucleic acid antigens were not detached from a solid phase by washing with 0.5 M NaCl solution indicated that the reduction of binding of anti-DNA antibodies in both MoAbs and naturally occurring antibodies was really due to dissociation of the antibodies from immune complexes. This is the first demonstration that DNA epitopes recognized by naturally occurring antibodies in both SLE and its mouse models are sensitive to neutral NaCl concentrations. This novel trait of naturally occurring antibodies will be very useful in studies on the nature of immune complexes in sera and kidneys of cases of systemic lupus erythematosus (SLE).