Primary structures and chain dominance of anti-DNA antibodies

Using several anti-DNA autoantibodies, we analyzed the relative involvement of heavy and light chains in their interactions with DNA, We previously ob tained eight hybridomas producing monoclonal anti-DNA autoantibodies by fus ing spleen cells from an MRL-lpr/lpr mouse with myeloma cells, The chain do minance was analyzed by UV cross-linking experiments, in which the antibodi es were covalently cross-linked with radioisotope-labeled oligonucleotides by short-wavelength UV-Light, and the cross-linked H and L chains were anal yzed by SDS-PAGE and densitometric scanning, Among these, three were found to be heavy chain dominant antibodies in which heavy chains are dominantly involved in DNA binding, The other five were co-dominant antibodies in whic h both heavy and light chains are involved in DNA binding. To determine the factor(s) that can explain the chain dominance in DNA binding, we determin ed the amino acid sequences of the variable regions of both heavy (VH) and light (VL) chains of all eight monoclonal antibodies, By analyzing the data , we were able to draw the following conclusions: (1) The arginine residues are found in the CDR3 region of both VH and VL of the co-dominant antibodi es; whereas, the same residues are found only in the CDR3s of VH, but not i n VL, of the heavy chain dominant antibodies. (2) The net charges of the V region affect the chain dominance. From the results of this study it is sug gested that the presence of arginine residue in CDR3 is a critical factor i n determining chain-dominance, as well as DNA binding of anti-DNA antibodie s in general.