Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type b polysaccharide. IV. The less frequently expressed VL are heterogeneous.

We previously demonstrated that the human anti-Haemophilus influenzae type b polysaccharide (Hib-PS) VL repertoire is dominated by a product of the V kappa II gene, A2, and that V kappa II-A2 anti-Hib-PS antibodies have little or no somatic mutation in VL. To further study this VL repertoire, we studied non-A2 anti-Hib-PS antibodies that were identified either serologically or by amino-terminal amino acid sequence analysis. Of 15 non-A2 anti-Hib-PS antibodies from 12 vaccinated adults, we found four V lambda, five V kappa I, one non-A2 V kappa II, four V kappa III, and one V kappa IV antibodies. As expected, all but two of these subjects also produced V kappa II-A2 antibodies. Interestingly, one of these subjects lacks the A2 gene in the germ line. However, both subjects who did not produce detectable V kappa II antibody did produce normal amounts of total anti-Hib-PS antibody after vaccination. Candidate V kappa genes for the non-A2 antibodies were identified by comparison of up to 60 VL amino acid residues, including CDR1 and CDR2, with all sequenced V kappa genes. V kappa I antibodies appear to be products of three newly sequenced V kappa I genes, O8, O18, and L11, that are reported here. The O8 and O18 genes encode identical amino acid sequences. The non-A2 V kappa II antibody is a likely product of the A1 or A17 genes, the V kappa III antibodies are likely products of the A27 gene, and the V kappa IV antibody is a product of the single V kappa IV gene, B3. Unlike V kappa II-A2 antibodies, the V kappa I, V kappa III, and V kappa IV antibodies differed by one to five CDR residues from the germ line product of the candidate genes, suggesting the presence of somatic mutations. Thus, anti-Hib-PS antibodies can be divided into two types, the most frequently observed A2 antibodies with little or no somatic mutation and non-A2 antibodies that likely contain somatic mutations.