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

We previously demonstrated that the human anti-Haemophilus influenzae type b polysaccharide (Hib-PS) VL repertoire is dominated by a product of the VκII gene, A2, and that VκII-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_λ, five VκI, one non-A2 VκII, four VκIII, and one VκIV antibodies. As expected, all but two of these subjects also produced VκII-A2 antibodies. Interestingly, one of these subjects lacks the A2 gene in the germ line. However, both subjects who did not produce detectable VκII antibody did produce normal amounts of total anti-Hib-PS antibody after vaccination. Candidate Vκ 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 Vκ genes. VκI antibodies appear to be products of three newly sequenced VκI genes, O8, O18, and L11, that are reported here. The O8 and O18 genes encode identical amino acid sequences. The non-A2 VκII antibody is a likely product of the A1 or A17 genes, the VκIII antibodies are likely products of the A27 gene, and the VκIV antibody is a product of the single VκIV gene, B3. Unlike VκII-A2 antibodies, the VκI, VκIII, and VκIV 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.