A THIOL ANTIOXIDANT REGULATES IGE ISOTYPE SWITCHING BY INHIBITING ACTIVATION OF NUCLEAR FACTOR-KAPPA-B

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 litt le information on whether this factor is involved in regulating IgE sy nthesis by human B cells. Accordingly, we studied the role of NF-kappa B in germline C epsilon transcription by using two human Burkitt's ly mphoma B cell lines, DND39 and DG75. In both cell lines, n-acetyl-L-cy steine (NAG), a potent thiol antioxidant, inhibited the triggering of the nuclear expression of NF-kappa B by IL-4 and by anti-CD40 monoclon al 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 STA T6 only partly blocked IL-4-induced germline C epsilon transcription. However, these two decoy oligodeoxynucleotides together almost complet ely abrogated IL-4-induced germline C epsilon transcription. Of note, CD40-mediated enhancement of IL-4-driven germline C epsilon transcript ion was markedly decreased by NAC or by a decoy oligodeoxynucleotide f or NF-kappa B. The effect of NAC was also examined on deletional switc h recombination underlying the isotype switch to IgE. NAC inhibited th e generation of S mu/S epsilon switch fragments in normal human B cell s costimulated with IL-4 and anti-CD40 monoclonal antibody. It also ab olished 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 c lass switching to IgE.