V-GENE-SEQUENCES OF LUPUS-DERIVED HUMAN-IGM ANTI-SSDNA ANTIBODY - IMPLICATION FOR THE IMPORTANCE OF THE LOCATION OF DNA-BINDING AMINO-ACIDS

Binding and structural characteristics of human IgMk anti-ssDNA antibo dy 7B3 were determined. 7B3 was derived from Epstein-Barr virus-transf ormed peripheral blood B cells of a lupus nephritis patient. Purified 7B3 bound ssDNA from various species, but not dsDNA or structurally un related antigens. The relative avidity of 7B3 was high in comparison w ith IgM anti-DNA antibodies previously described by other investigator s. Sequence analysis showed that 7B3 used V(H)26/D35/J(H)3 and Humkv32 8h5/J(K)1 germline genes, and had a few mutations in the complementari ty determining regions (CDRs). No arginine was expressed in the heavy- chain CDR3. However, the putative DNA contact sites, based on the prev ious crystallographic and computer modeling studies, were occupied by mutated or germline-derived basic and polar amino acids. These results suggest that a minimally mutated IgM anti-ssDNA antibody with a pauci ty of arginines could display monospecificity and high avidity if DNA- binding amino acids are enriched at the critical DNA contact sites. (C ) 1998 Academic Press.