MOLECULAR MAPPING OF THE 8.12 SLE-ASSOCIATED IDIOTYPE SPECIFICITY AT THE SINGLE AMINO-ACID LEVEL

The 8.12 idiotype is expressed in elevated titer in the serum of patie nts with systemic lupus erythematosus and is a marker for a subpopulat ion of anti-DNA antibodies that possess a V gamma II encoded light cha in. This study utilized a eukaryotic expression system to identify the structural basis for expression of this idiotype. Reversion of the 8. 12(+) DSC light chain to the hs1v215.23/DPL11 germline gene reveals th at the 8.12 idiotype is encoded in the germline. The 8.12(+) DSC and t he 8.12(-)AS17 light chains, both belonging to the VIII family, were s ubjected to site directed mutagenesis, to localize amino acids importa nt for expression of the 8.12 idiotype. Point mutations were performed in CDR1, CDR2, FR3 and CDR3, in positions where the 8.12(+) DSC diffe rs from the 8.12(-)AS17. Amino acids in CDR1 and the CDR2 proximal reg ion of FR3, but not the J proximal region of CDR3, play a crucial role in 8.12 reactivity. The 3-D structure of Meg, a human IgG1, with whic h DSC shares a sequence homology of 92.3% has been examined to visuali ze the effect of each of the mutations and to identify the surface on DSC that comprises the idiotype. (C) 1997 Elsevier Science Ltd.