kappa-Chain restriction in anti-galactan antibodies

Complete kappa-chain variable region sequences were determined for 10 light chains from anti-beta-(1,6)-D-galactan-binding monoclonal antibodies. Eight of these light chains were from IgM and two from IgG proteins. Seven of the eight IgM light chains were identical from position 1 to 95, the region encoded by the light chain variable region gene. The eighth differed at a single framework position. The two IgG light chains were identical in sequence and differed from the IgM light chains at two framework positions. All 10 light chains have an lle at position 96, as has been previously reported in 5 of 6 anti-galactan myeloma proteins. This residue is the first amino acid normally encoded by the light chain J gene. None of the germ line J genes encodes an lle at position 96, and furthermore the lle codon cannot be generated by alterations in the frame of recombination between the codon for amino acid 95 and J gene codons. These light chains are thus the product of an unusual and reproducible recombination event that appears to employ an extra codon at the 3' end of the variable region gene. Three different J segments are potentially used in these light chains J1 or J2 was found in three chains and J5 in seven.