Specific antibody production by V(H)-gene replacement

V(H)-gene replacement is a recombination event in which a pre-existing immunoglobulin heavy chain gene can be altered by the replacement of the rearranged V(H) gene segment with another V(H) gene segment. Although this event has been demonstrated in various model systems, its role in generating antibody diversity is still unsettled. We have used a genetically modified mouse strain, QM, with a quasi monoclonal primary B cell repertoire specific for NP to determine whether V(H) gene replacement can generate a new antigen specificity. Hybridomas generated from QM splenocytes after immunization with different antigens, gave rise to antibodies with specificity to the immunizing antigen or with new specificities. We found V(H)-gene replacement was used to change the original heavy chain gene rearrangement specific for NP into a heavy chain gene encoding the new antigen specificity. V(H)-gene replacement intermediates were detected both before and after the immunization, suggesting that the event was selective rather than instructive. These results demonstrate that V(H)-gene replacement can generate a new antibody heavy chain gene with a different functional and selectable antigen specificity.