B-CELLS FROM P50 NF-KAPPA-B KNOCKOUT MICE HAVE SELECTIVE DEFECTS IN PROLIFERATION, DIFFERENTIATION, GERM-LINE C-H TRANSCRIPTION, AND IG CLASS SWITCHING/

To better understand the role of NF-kappa B in normal B cell physiolog y, we used a purified population of resting B cells from p50/NF-kappa B knockout (p50(-/-)) mice to determine their ability to proliferate, secrete Ig, express germ-line C-H RNA, and undergo Ig isotype switchin g in vitro in response to a number of distinct stimuli. p50(-/-) B cel ls proliferated normally in response to dextran-anti-IgD Abs (alpha de lta-dex) and membrane-bound, but not soluble, CD40 ligand (CD40L), and they were virtually unresponsive to LPS when compared with control B cells. p50(-/-) B cells secreted markedly reduced Ig in response to al pha delta-dex or mCD40L in the presence of IL-4 + IL-5, despite their relatively normal proliferative rates, whereas normal Ig secretion was restored by the combination of alpha delta-dex and CD40L. p50(-/-) B cells expressed normal steady-state levels of germ-line C-H gamma 1 an d C-H alpha RNA but markedly reduced germ-line C-H gamma 3 and CHE RNA upon appropriate stimulation. Although p50(-/-) B cells underwent sub stantial switching to IgG1, a marked reduction in the switch to IgG3 a nd IgE, as well as IgA, was observed. These data are the first to demo nstrate key, independent roles for p50/NF-kappa B in normal B cell mat uration to Ig secretion, germ-line C, gene activation, and Ig class sw itching, as well as mitogenesis, and provide a powerful and well-defin ed in vitro model system for studying the role of p50/NF-kappa B in a wide range of normal cellular functions.