Defining the structural correlates responsible for loss of arsonate affinity in an IDCR antibody isolated from an autoimmune mouse.

Immunization of the autoimmune mouse strain (M x A) Id/lpr with Ars-KLH, has been shown to elicit a prolonged anti-Ars IdCR response similar to that found in A/J mice. Cell fusion of splenocytes from a diseased mouse previously immunized with Ars-KLH resulted in a monoclonal antibody, 1-52.30, that was found to express the strain A major cross-reactive idiotype, but failed to bind Ars. Nucleotide sequence analysis demonstrated that 1-52.30: (a) used the "canonical" combination of gene segments associated with this idiotype, and (b) exhibited a pattern of somatic mutation consistent with selection for high affinity Ars binding. Two amino acids, VL 91 and 93, were mutated in 36-65, the germline equivalent of the IdCR antibodies, to 1-52.30-like residues (91G-->D, 93T-->M). The results of the mutagenesis showed that changing a single light chain residue, VL 91, from glycine to aspartic acid, resulted in a dramatic loss of Ars binding activity.