Regulation of receptor editing by NF-kappaB

V(D)J recombination is a series of site specific DNA recombination reactions responsible for the assembly of immunoglobulin (Ig) and T cell receptor (TCR) variable region exons. This is a highly regulated process in regard to cell lineage, stage of development, and expression of only one rearranged allele per cell (allelic exclusion). Because of the extreme diversity of both Ig and TCR, tolerance mechanisms are necessary to ensure that B and T cells do not activate in response to self-ligands. In B cells, one such tolerance mechanism is called receptor editing. If the B cell receptor (BCR) recognizes a self-ligand at the immature stage of development, the BCR is downregulated and further light chain gene rearrangements are made in an attempt to edit the specificity of auto-reactive receptor. Many questions remain as to how receptor editing is regulated.;This thesis describes experiments aimed at determining the role of the transcription factor NF-kappaB in the regulation of receptor editing. Analysis of a heterozygous mutant mouse in which the NF-kappaB dependent IkappaBalpha gene was replaced with a lacZ reporter cDNA (IkappaBalpha+/lacZ ) revealed a bimodal pattern of reporter expression at the pre-B stage of development. An analysis of pre-B cells sorted based on the product of lacZ, beta-galactosidase activity revealed an increase in both kappa and lambda light chain gene rearrangements in the beta-gal positive cells, although RAG levels were indistinguishable. Wild type bone marrow infected with an IkappaBalpha super repressor have reduced rearranged lambda transcripts and reduced germline kappa transcripts, but expressed similar levels of RAGs compared to vector control. These data confirm the importance of NF-kappaB in light chain rearrangement. Pre-B cells expressing beta-gal also showed an increase in various markers of receptor editing. IkappaBalpha +/lacZ reporter mice were mated to mice with either innocuous or self-specific knocked in BCRs. beta-gal was only expressed in the mice with self-specific BCRs, providing further evidence that NF-kappaB is active in cells undergoing receptor editing. Runqing Lu's lab has recently shown that IRF4 contributes to the regulation of IgLC and IRF4 transcripts are upregulated in pre-B beta-gal positive cells. IRF4 is a target of NF-kappaB, suggesting that NF-kappaB could be acting through IRF4 to regulate receptor editing.