Divergent roles for TLR7 and TLR9 in modulating the NFkB pathway in B cells 2261147

Abstract Introduction BCR signal strength plays a key role in the fate decision of B cells with strong BCR signals promoting plasma cell differentiation and weaker BCR signals driving germinal center formation. Signals through toll-like receptors (TLRs) also influence B cell differentiation. It is still unclear how the BCR and TLR signaling cascades interface to modulate B cell responses and differentiation. Using the BCR sdTg mouse model AM14 we reported earlier that BCR/TLR7-activated AM14 B cells differentiate into short-lived plasmablasts while plasma cell development does not occur in BCR/TLR9-activated AM14 B cells. Methods To better understand the signaling differences in BCR/TLR7 and BCR/TLR9 activated B cells, we activated purified AM14 B cells with RNA and DNA containing immune complexes and measured the activation of NFkB by Western blot analysis. We measured IkBz and BATF expression in these B cells at different timepoints by RT-PCR and Western blot. Furthermore, B cells from IkBz-deficient and BATF-deficient mice were activated with immune complexes and plasmablast differentiation was measure after 72 hours by flow cytometry. Results Intriguingly, we now show that BCR/TLR9 activation induces a more pronounced NFkB signal and the expression of the non-classical IkB member IkBz. BCR/TLR7-activated AM14 B cells are unable to sustain the initial NFkB response and fail to express IkBz. IkBz is known to be important in regulating cytokine responses in T cells and macrophages. However, its role in B cells is not well defined. We find that several IkBz regulated cytokines are expressed after BCR/TLR9 dependent signaling but not after BCR/TLR7 dependent signaling. Furthermore, we show that expression of IkBz inhibits plasma cell formation by regulating the expression of the transcription factor BATF. Conclusion Our results point to divergent roles for TLR7 and TLR9 in modulating the NFkB signaling cascades, leading to differential expression of NFkB target genes which influence B cell fate decisions. Funding Source LRA Target Identification in Lupus 2016 (KN), NIH 1R21AR076007-01A1 (KN) Topic Categories Lymphocyte Differentiation and Peripheral Maintenance (LYM)