The NF-kappaB canonical pathway is involved in the control of the exonucleolytic processing of coding ends during V(D)J recombination.

V(D)J recombination is essential to produce an Ig repertoire with a large range of Ag specificities. Although NF-κB-binding sites are present in the human and mouse IgH, Igκ, and Igλ enhancer modules and RAG expression is controlled by NF-κB, it is not known whether NF-κB regulates V(D)J recombination mechanisms after RAG-mediated dsDNA breaks. To clarify the involvement of NF-κB in human V(D)J recombination, we amplified Ig gene rearrangements from individual peripheral B cells of patients with X-linked anhidrotic ectodermal dysplasia with hyper-IgM syndrome (HED-ID) who have deficient expression of the NF-κB essential modulator (NEMO/Ikkγ). The amplification of nonproductive Ig gene rearrangements from HED-ID B cells reflects the influence of the Ikkγ-mediated canonical NF-κB pathway on specific molecular mechanisms involved in V(D)J recombination. We found that the CDR3H from HED-ID B cells were abnormally long, as a result of a marked reduction in the exonuclease activity on the V, D, and J germline coding ends, whereas random N-nucleotide addition and palindromic overhangs (P nucleotides) were comparable to controls. This suggests that an intact canonical NF-κB pathway is essential for normal exonucleolytic activity during human V(D)J recombination, whereas terminal deoxynucleotide transferase, Artemis, and DNA-dependent protein kinase catalytic subunit activity are not affected. The generation of memory B cells and somatic hypermutation were markedly deficient confirming a role for NF-κB in these events of B cell maturation. However, selection of the primary B cell repertoire appeared to be intact and was partially able to correct the defects generated by abnormal V(D)J recombination.