Structure of primary anti‐(4‐hydroxy‐3‐nitro‐phenyl)acetyl (NP) antibodies in normal and idiotypically suppressed C57BL/6 mice

Abstract

Eight monoclonal antibodies from the primary response of C57BLJ6 mice against the hapten (4-hydroxy-3-nitrophenyl)acetyl (NP) were isolated. The antibodies carry λ1 light chains and have similar affinities for the immunizing hapten. Sequence analysis at the level of mRNA reveals that all antibodies express the V_H gene 186.2 and all but one the DF116.1 gene segment. The J segment of the heavy chain is J_H2 in six cases and J_H4 in two. Somatic point mutations are scarcely detectable in the antibodies, but there is extensive sequence variability at the boundaries of the D gene segment, mainly at its 5′ end. However, seven of eight antibodies express tyrosine in position 99 of the heavy chain, encoded either by the 5′ codon of DF116.1 or by presumed N sequences. In the former case, the tyrosine is the first of a stretch of three (positions 99–101). In the latter, a similar stretch (positions 99, 101, 102) is interrupted by aspartic acid, asparagine or cysteine in position 100. These variations profoundly affect idiotypic specificity. Six of the eight monoclonal antibodies came from mice neonatally suppressed by an anti-idiotope antibody whose target idiotope is regularly expressed in primary anti-NP responses and depends upon a non-germ-line-encoded aspartic acid in position 100 of the heavy chain. The sequence data show that the mice circumvent suppression by expressing antibodies which lack this aspartic acid but are otherwise structurally very similar to anti-NP antibodies from normal animals. Since suppression in the animals is partly controlled by regulatory T cells, we conclude that these T cells are highly restricted in their specificity in that they preferentially see a determinant which also depends upon the aspartic acid in position 100. The data suggest that the V_H to D boundary serves as a target of idiotypic selection.