Antibodies to rabies virus display biased utilization of Vκ but not Vλ genes, junctional diversity, and somatic hypermutation

To gain insight into the clonal composition and somatic diversification of the human antibody response to thymus-dependent (TD) antigens, we analyzed the sequences of the Vκ and Vλ genes of four IgM, five IgG1, and one IgA1 mAbs to rabies virus, generated using B cells from healthy subjects vaccinated with rabies virus vaccine. The selection of the Vκ but not of the Vλ genes of the rabies virus Abs was biased when compared to the representation of the Vκ genes in the human haploid genome. The mAb V_L gene utilization vastly overlapped with that of Vκ-Jκ and Vλ-Jλ rearrangements expressed in the human B cell repertoire at large, and that of other TD antibodies, but differed sharply from that utilized by antibodies to the thymus-independent (TI) Haemophilus influenzae type b polysaccharide. When compared to those of the respective germline sequences, the anti-rabies virus mAb of V_L gene sequences displayed a number of replacement (R) mutations, which were significantly more frequent in the CDRs of at least two high affinity mAbs, the IgG1κ mAb58 and the virus-neutralizing IgG1λ mAb57. This process of Ag-dependent somatic diversification was superimposed by frequent truncations at the 3′ end of the V genes and unencoded micleotide additions to yield highly heterogeneous CDR3s. Thus, the specific human antibody response to proteinic TD antigens can be biased and is somatically diversified.