Regulatory regions 3' of the immunoglobulin heavy chain intronic enhancer differentially affect expression of a heavy chain transgene in resting and activated B cells.

We have compared the expression patterns of three Ig heavy chain transgenes. The three constructs differ only by deletion of J-C intron sequences located downstream of the Emu enhancer region. When stably transfected into a myeloma cell line, all three constructs are expressed at comparable levels. However, transgenic mice carrying each construct show dramatic differences in transgene expression. Our results indicate that, in addition to the Emu enhancer, at least two regions, RegA and RegS, within the J-C intron influence transgene expression. RegA, located directly downstream of the core Emu enhancer, is involved in up-regulation of transgene expression after LPS activation of splenocytes. RegS, located within or downstream of the Smu switch region, is important for normal levels of transgene expression in splenocytes of heavy chain transgenic mice.