The complete amino acid sequence of the light chain variable region of two monoclonal anti-p-azobenzene-arsonate antibodies bearing the cross-reactive idiotype.

Two monoclonal anti-p-azobenzene-arsonate antibodies produced by cell fusion of A/J spleen lymphocytes were selected. It had previously been shown that they both expressed the cross-reactive idiotype (CRI) and that the amino terminal sequence of their heavy chain variable region differed by only one amino acid substitution within the first 55 residues, at residue 41 in the second framework region. A novel, sensitive peptide-mapping method had indicated that the light chain of these two antibodies differed by at least three amino acid substitutions. Here, the complete amino acid sequence of the light chain variable region is presented. There are only 3 amino acid substitutions between the two antibodies, located in the first and second complementarity determining regions and the third framework region respectively. Although the variable region of the light chains of these two monoclonal antibodies show such a high degree of homology they differ by 26 and 27 substitutions from the reference sequence of the light chain of CRI+ anti-ABA serum antibodies. In addition, they are homologous to 4 other such CRI+ monoclonal antibody light chain sequences published so far, in which only 2 of the above 3 substitutions are not represented. The contribution of the light chain to the CRI is discussed.