Complete heavy and light chain variable region sequence of anti-arsonate monoclonal antibodies from BALB/c and A/J mice sharing the 36-60 idiotype are highly homologous.

Structural and serologic studies on murine A/J monoclonal anti-arsonate antibodies resulted in the identification of a second idiotype family (Id36-60) in addition to the predominant idiotype family (IdCR). Id36-60, unlike IdCR, is a dominant idiotype in the BALB/c strain but is a "minor" idiotype in the A/J strain. The complete heavy and light chain variable region (VH and VL) amino acid sequences of a representative Id36-60 hybridoma protein from both the A/J and BALB/c strains have been determined. There are only four amino acid sequence differences between the VH of antibody 36-60 (A/J) and antibody 1210.7 (BALB/c). Two of these differences arise from single nucleotide changes in which the A/J and BALB/c Id36-60 VH germline gene sequences differ. The two other differences are the result of somatic mutation in hybridoma protein 36-60. In addition, Id36-60 heavy chains employ the same D and JH3 segments in both strains. The entire Vk2 VL of 36-60 and 1210.7 differ by only two amino acids, suggesting that like the heavy chains, they are derived from highly homologous VL genes. The same Jk segment is used in both antibodies. A comparison of the amino acid sequence data from Id36-60-bearing hybridomas suggests that a heavy chain amino acid difference accounts for the diminished arsonate binding by the 1210.7 hybridoma protein. Because the 1210.7 heavy chain is the unmutated product of the BALB/c VH gene, somatic mutation in VH may be required to enhance Ars affinity in this system.