The role of the immunoglobulin heavy chain in human anti‐dna antibody binding specificity

Objective. To investigate the structural basis for DNA binding of the natural human IgMλ monoclonal antibody KIM4.6. Methods. An IgMλ, non–DNA‐reactive variant hybridoma was derived during in vitro subcloning of the anti‐DNA antibody KIM4.6. The variable (V)‐region heavy (H) and light (L) chain genes expressed by the variant hybridoma were amplified by polymerase chain reaction, cloned, sequenced, and compared with those of the KIM4.6 parent and other DNA‐binding and non–DNA‐binding antibodies. Results. The VL chain of the variant was identical to that of KIM4.6. In contrast, the VH chain was completely different from the VH chain of the parent but was similar or identical, except in the diversity (D) and joining regions, to the VH chain of the systemic lupus erythematosus (SLE) IgG anti‐DNA antibody T14 and SLE IgM nephritogenic anti‐DNA antibodies NE‐1 and NE‐13. Conclusion. The expression of the KIM4.6 VL chain is not sufficient for DNA specificity. The VH chain and its D region play a key role in conferring DNA binding of the KIM4.6 anti‐DNA antibody. Copyright © 1995 American College of Rheumatolog