LIGHT-CHAIN CONTRIBUTION TO SPECIFICITY IN ANTI-DNA ANTIBODIES

We studied mice expressing one of two H chain transgenes. Both transge nes expressed the same 3H9 anti-DNA VDJ, but differed in their constan t domains. The IgM transgene efficiently induced tolerance and selecte d for a subset of endogenous L chains that prevented dsDNA binding. In contrast, the IgG2b secreted-only H chain allowed expression of a bro ad range of L chains, most of which yielded anti-dsDNA Ab. To deduce t he features of L chains that affect DNA binding, we derived hybridomas from LPS-stimulated splenic B cells from the two transgene lines and compared the VK sequences of Ab they secreted. identification of L cha ins with related sequences but different binding to ssDNA, dsDNA, and cardiolipin allowed us to pinpoint L chain residues that correlate wit h enhanced or reduced binding. Arginines at the junction of V kappa 1 or V kappa 8 regions and J kappa 1, and arginines or asparagines in CD R1 or CDR2 enhanced DNA binding. Negatively charged residues at the sa me positions were found to interfere with binding. Thus, we predict th at appropriate amino acids at these positions may form contacts with D NA. The likely locations of contact residues in the combining site wer e evaluated by inspection of previously determined Ab structures. Our results indicate that L chains in anti-DNA Ab are able to modulate DNA binding and contribute contact sites for additional determinants on a complex autoantigen.