Idiotypic selection of an antibody mutant with changed hapten binding specificity, resulting from a point mutation in position 50 of the heavy chain.

Somatic mutation occurs at a low rate in the rearranged antibody V region genes of the hybridoma line B1-8. delta 1 which expresses an antibody with specificity for the hapten 4-hydroxy-3-nitro-5-iodo-phenylacetyl (NIP). A mutant was selected which had lost a binding site-related idiotope but retained most of its other idiotypic determinants. The mutant had concomitantly lost NIP binding and acquired specificity for dinitrophenylated bovine serum albumin. It carried a single point mutation in position 50 of the heavy chain, resulting in the replacement of an arginine by a glycine.