Deletion of the IgH enhancer does not reduce immunoglobulin heavy chain production of a hybridoma IgD class switch variant.

Immunoglobulin (Ig) gene promotors are active only in cells of the B-lymphocyte lineage. Transfection experiments have shown that this is due in part to tissue specific 'activating' DNA sequences, so called enhancers. It is not entirely clear whether these sequences are necessary for initial activation or also for maintenance of transcription of a gene. We describe here the isolation and characterisation of a mouse hybridoma cell line that has deleted in vitro the 'activating' sequence from the active IgH locus, the only IgH locus it contains. Nevertheless, Ig heavy chain production of the variant cell is not impaired and remains comparable with that of other hybridoma cells. Therefore, a high rate of Ig heavy chain production in antibody-producing cells is either independent of any sequences enhancing transcription or else these can easily be replaced by other DNA sequences with a similar function that have been moved into the vicinity of the V region.