ABSTRACT
During T cell-dependent immune responses in mouse and human, Ig genes diversify by somatic hypermutation within germinal centers. Rabbits, in addition to using somatic hypermutation to diversify their IgH genes, use a somatic gene conversion-like mechanism, which involves homologous recombination between upstream VH gene segments and the rearranged VDJ genes. Somatic gene conversion and somatic hypermutation occur in young rabbit gut-associated lymphoid tissue and are thought to diversify a primary Ab repertoire that is otherwise limited by preferential VH gene segment utilization. Because somatic gene conversion is rarely found within Ig genes during immune responses in mouse and human, we investigated whether gene conversion in rabbit also occurs during specific immune responses, in a location other than gut-associated lymphoid tissue. We analyzed clonally related VDJ genes from popliteal lymph node B cells responding to primary, secondary, and tertiary immunization with the hapten FITC coupled to a protein carrier. Clonally related VDJ gene sequences were derived from FITC-specific hybridomas, as well as from Ag-induced germinal centers of the popliteal lymph node. By analyzing the nature of mutations within these clonally related VDJ gene sequences, we found evidence not only of ongoing somatic hypermutation, but also of ongoing somatic gene conversion. Thus in rabbit, both somatic gene conversion and somatic hypermutation occur during the course of an immune response.
Subject(s)
Antibody Diversity/genetics , Gene Conversion/immunology , Genes, Immunoglobulin , Haptens/immunology , Immunoglobulin Heavy Chains/genetics , Point Mutation/immunology , Amino Acid Sequence , Animals , Base Sequence , Cell Lineage/genetics , Cell Lineage/immunology , Clone Cells , Cloning, Molecular , Fluorescein-5-isothiocyanate , Germ-Line Mutation/immunology , Germinal Center/immunology , Germinal Center/metabolism , Hybridomas , Immunoglobulin Variable Region/genetics , Molecular Sequence Data , Rabbits , Serum Albumin/immunologyABSTRACT
Most rabbit B lymphocytes use the same VH gene in V(D)J gene rearrangements and undergo somatic diversification by gene conversion and hypermutation. Recent experiments have shown that V(D)J genes in essentially all rabbit B cells diversify shortly after birth and that this diversification occurs in the gut-associated lymphoid tissue. Still to be determined is whether this diversification is developmentally programmed or is driven by exogenous microbial antigens.
