DEFINING THE STRUCTURAL CORRELATES RESPONSIBLE FOR LOSS OF ARSONATE AFFINITY IN AN ID(CR) ANTIBODY ISOLATED FROM AN AUTOIMMUNE MOUSE

Immunization of the autoimmune mouse strain (M x A) Id/lpr with Ars-KL H, has been shown to elicit a prolonged anti-Ars Id(CR) response simil ar to that found in A/J mice. Cell fusion of splenocytes from a diseas ed mouse previously immunized with Ars-KLH resulted in a monoclonal an tibody, 1-52.30, that was found to express the strain A major cross-re active idiotype, but failed to bind Ars. Nucleotide sequence analysis demonstrated that 1-52.30: (a) used the ''canonical'' combination of g ene segments associated with this idiotype, and (b) exhibited a patter n of somatic mutation consistent with selection for high affinity Ars binding. Two amino acids, V(L) 91 and 93, were mutated in 36-65, the g ermline equivalent of the Id(CR) antibodies, to 1-52.30-like residues (91G-->D, 93T-->M). The results of the mutagenesis showed that changin g a single light chain residue, V, 91, from glycine to aspartic acid, resulted in a dramatic loss of Ars binding activity.