Molecular characterization of human antibodies to bacterial antigens: Utilization of the less frequently expressed V H2 and V H6 heavy chain variable region gene families

Abstract

Structural analysis of the human immunoglobulin repertoire holds promise for determining the basis of variable region gene usage in response to a variety of auto and exogenous antigens. Here we report the nucleotide sequences of the heavy and light chain variable regions expressed by three human monoclonal antibodies specific for two clinically relevant bacterial pathogens, Bordetella pertussis and Haemophilus influenzae type b. The cell lines were derived by in vitro stimulation of lymphocytes from spleen or tonsillar tissue, respectively, and bind to different antigens from the two organisms. The single B. pertussis antibody is of the IgMγ. isotype and utilizes the single V H6 gene segment in combination with a V γ2 gene and demonstrates limited somatic mutation, yet is highly indicative of an antigen-driven immune response. One H. influenzae antibody is of the IgG2γ isotype and expresses a V H 3 gene segment with a V γ 1 gene, while the second cell line produces an IgG3 γ antibody expressing a combination of V H2 V γ3 . Both molecules show evidence of somatic mutation. The D gene segments of the heavy chains vary in length and display limited sequence homology with known germline D segments. As demonstrated previously, J H4 predominates (two J H4 and one J H3) and all three utilize the J γ3 gene segment. In addition, we have isolated and sequenced a number of germline V H2 gene segments in an attempt to better understand the nature of the V H2 germline repertoire. In addition to contributing to the understanding of the human antibody repertoire, such clinically relevant molecules may prove to be a source of passive immunotherapy for those at risk to developing disease.