A thiol antioxidant regulates IgE isotype switching by inhibiting activation of nuclear factor-κB

The binding site for nuclear factor-kappa B (NF-kappa B) is present at the promoter region of the germline C epsilon gene, but there is little information on whether this factor is involved in regulating IgE synthesis by human B cells. Accordingly, we studied the role of NF-kappa B in germline C epsilon transcription by using two human Burkitt's lymphoma B cell lines, DND39 and DG75. In both cell lines, n-acetyl-L-cysteine (NAG), a potent thiol antioxidant, inhibited the triggering of the nuclear expression of NF-kappa B by IL-4 and by anti-CD40 monoclonal antibody. Although IL-4 activated signal transducers and activators of transcription (STAT) 6 in addition to NF-kappa B, NAC treatment or the transfection of decoy oligodeoxynucleotides for NF-kappa B or STAT6 only partly blocked IL-4-induced germline C epsilon transcription. However, these two decoy oligodeoxynucleotides together almost completely abrogated IL-4-induced germline C epsilon transcription. Of note, CD40-mediated enhancement of IL-4-driven germline C epsilon transcription was markedly decreased by NAC or by a decoy oligodeoxynucleotide for NF-kappa B. The effect of NAC was also examined on deletional switch recombination underlying the isotype switch to IgE. NAC inhibited the generation of S mu/S epsilon switch fragments in normal human B cells costimulated with IL-4 and anti-CD40 monoclonal antibody. It also abolished IL-4-induced upregulation of CD40 but promoted upregulation of CD23. These results suggest that coordination of NF-kappa B and STAT6 may be required for induction of germline C epsilon transcription by IL-4, and that CD40-mediated NF-kappa B activation may be important in regulating both enhancement of germline C epsilon transcription and class switching to IgE.