Immunoglobulin V region variants in hybridoma cells. II. Recombination between V genes.

The mouse hybridoma line B1‐8.delta 1 secretes a monoclonal IgD, lambda 1 anti‐(4‐hydroxy‐3‐nitrophenyl)acetyl (NP) antibody with defined idiotypic determinants. Two spontaneous V‐region variants (B1‐8.V1/V2) with altered idiotope pattern were selected and the structural variation was located to the variable region of the heavy chain. The amino acid sequences of the B1‐8. delta 1 and variant heavy chain V regions were determined. The variant VH regions are identical. Wild‐type and variant VH regions differ in 10 positions. Single amino acid exchanges are found in the first and second framework at positions 20 and 43. The majority of replacements (eight substitutions) is clustered in the second complementary‐determining region (CDR 2). There are no differences in CDR 1 and CRD 3 and the JH region. The variant, which at first glance appears to have undergone a series of point mutations, arose by recombination, possibly gene conversion, between the rearranged VDJ gene of the wild‐type (B1‐8.delta 1) and a neighbouring germ line VH gene encoding all of the substitutions.