DUAL REACTIVITY OF SEVERAL MONOCLONAL ANTI-NUCLEOSOME AUTOANTIBODIES FOR DOUBLE-STRANDED DNA AND A SHORT SEGMENT OF HISTONE H3

We have shown previously that four IgG monoclonal autoantibodies (mAbs ) reacted in ELISA with both double-stranded (ds) DNA and peptide 83-1 00 of histone H3. The peptide 83-100 contains a cysteine residue at po sition 96 and readily dimerizes at pH 7-8. We describe here that only the 83-100 dimers, and not the 83-100 monomers, are recognized by the four antibodies and inhibit in ELISA the binding of mAbs to dsDNA. The equilibrium affinity constants (K-a) and kinetic rate constants of tw o of these mAbs were measured in a biosensor system. K-a values were s ignificantly higher when these mAbs were tested with dsDNA as compared with the 83-100 dimer. Further higher K-a values were measured with m ononucleosomes containing DNA and histones. It is proposed that these four mAbs are directed against a topographic determinant formed by DNA and the region 83-100 of H3 present as a dimer at the surface of nucl eosome, and that they react, although significantly less well, with DN A and peptide dimer tested separately. This study provides a quantitat ive and kinetic basis to interaction between several antibodies and di stinct antigenic structures and allows us to better understand the str uctural basis of apparent autoantibody cross-reactivity.