NF-κB binds to the immunoglobulin Sγ3 region in vivo during class switch recombination

Ig class switch recombination (CSR) is dependent upon the expression of activation-induced deaminase and targeted to specific isotypes by germ-line transcript expression and isotype-specific factors. NF-kappa B plays critical roles in multiple aspects of B cell biology and has been implicated in the mechanism of CSR by in vitro binding assays and altered S/S junctions derived from NF-kappa B p50-deficient mice. However, the pleiotropic contributions of NF-kappa B to gene expression in B cells has made discerning a direct role for NF-kappa B in CSR difficult. We now observe that binding of NF-kappa B components p50 and p65 is detected on S gamma 3 in vivo following lipopolysaccharide (LPS) activation and repressed by LPS + IL-4, suggesting a direct role for this factor in CSR. In vivo footprinting confirms occupancy of a previously defined NF-kappa B recognition site in S gamma 3 with the same temporal kinetics as found in the chromatin immunoprecipitation analysis. Binding of NF-kappa B components p50 and p65 was also detected on S gamma 1 following B cell activation. H3 histone hyper acetylation at S gamma 1 is strongly correlated with NF-kappa B binding, suggesting that NF-kappa B mediates chromatin remodeling in the S gamma 3 and S gamma 1 region.