Abstract

The immunoglobulin heavy chain repertoire is generated by somatic rearrangement of variable (V(H)), diversity (D(H)), and joining (J(H)) elements. It can be further diversified by V(H) replacement, where nonrearranged V(H) genes invade preexisting V(H)D(H)J(H) joints. To study the impact and mechanism of V(H) replacement, we generated mice in which antibody production depends on the replacement of a nonproductive V(H)D(H)J(H) rearrangement inserted into its physiological position in the immunoglobulin heavy chain locus. In these mice a highly diverse heavy chain repertoire resulted from V(H) replacement and a second process of noncanonical V(D)J recombination, direct V(H) to J(H) joining. V(H) replacement rarely generated detectable sequence duplications but often proceeded through recombination between the conserved homologous sequences at the 3' end of V(H). Thus, V(H) replacement is an efficient mechanism of antibody diversification, and its impact on the overall antibody repertoire could be greater than anticipated because it frequently leaves no molecular footprint.