NF-kB activation and function in B lymphocytes

National Institute On Aging

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Abstract

During fiscal year 2010 we accomplished the following: 1) We completed in vivo B cell priming experiments in collaboration with Dr. Mark Shlomchik (Yale University). We used mIgM-Tg mice;these mice carry a VH186.2 IgH transgene that lacks secretory exons bred to JH- and JK-deficient background. mIgM-Tg mice therefore express transgenic IgH protein complexed to lambda light chain. Approximately half the B cells in this mouse (that express Vλ1) bind the hapten NP. We injected mice with NP-BSA in PBS or PBS alone. To recapitulate pulse BCR activation, we isolated splenic B cells 2h after immunization, rested them for 4h, and re-stimulated with anti-CD40. By gating on antigen binding cells during flow cytometry we found that 2h antigen exposure in vivo enhanced the responsiveness of only antigen-specific cells to CD40 stimulation. Analysis of mRNA from short-term in vivo immunized B cells showed increased expression of several pulse-specific genes identified in the in vitro experiments. Our observations lead to a new working model for the initiation of T-dependent immune responses. 2) We completed our studies of c-Rel function during two phases of BCR-induced NF-κB activation in collaboration with Dr. Steve Gerondakis (Burnet Institute, Australia). 3) We initiated analyses of time-dependent gene expression profiling in B cells with the objective of understanding the function of NF-κB during G1 progression of B cells in response to BCR signaling. We used BCAP-deficient and PKCβ-deficient B cells to interrupt NF-κB activation. Gene expression profiling revealed a 30% overlap between genes that were down-regulated in each of these genotypes. We hypothesize that NF-κB target genes are a subset of these genes. Interestingly, pathway analysis of gene expression changes in these mutant backgrounds revealed that many 'immune response" associated pathways were up-regulated. These observations suggest that NF-κB proteins may suppress immune response pathways and accentuate cell-cycle progression pathways during early phases of T-independent immune responses.