Background/Purpose: In autoimmune prone BXD2 mice, abnormally upregulated IL-17 acts through NF-ĸB p65 role to promote the spontaneous germinal center response and autoantibody production. Recently, a pre-germinal center defect in the early transitional B cell development of autoimmune BXD2 mice was identified. This defect was characterized by accelerated B cell development, a feature which was normalized by IL-17RA deficiency on the BXD2 background. The hypothesis of this work is that IL-17 induced NF-ĸB regulates transitional B cell development

Methods: Using a B cell antigen tetramer, La_13-27 autoreactive B cells from the spleens of B6, autoimmune wild-type (WT) BXD2, and BXD2-Il17ra^–⁄– mice were analyzed by FACS for the development of CD93⁺ transitional B cell subsets. Intracellular phospho-flow was used to determine levels of phospho-p65 (p-p65) and total phospho-tyrosine following anti-IgM (5 µg/mL) stimulation at different time points. Super-resolution molecular imaging (STORM) was carried out to visualize p65 and p50 in BXD2-Il17ra^–⁄– B cells. WT BXD2 and BXD2-Il17ra^–⁄– were treated in vivo with AdIL-17 or AdIL-17RA:Fc to enhance or block endogenous IL-17RA signaling, respectively. Activation vs anergic responses were assessed by Dojindo cell survival assay following anti-IgM stimulation. 

Results: There was an enhanced BXD2-Il17ra^–⁄– transitional B cell anergy phenotype in vivo, which was characterized by a normalized La_13-27⁺ transitional B cell development compared with WT BXD2. BXD2-Il17ra^–⁄– B cells further exhibited strong anergic responses to BCR or TLR7 stimulation in vitro. The strong anergic phenotype of BXD2-Il17ra^–⁄– mouse B cells was associated with a dramatically enhanced nuclear expression of NF-ĸB1 (p50) and down-modulation of NF-ĸB p-p65. Super-resolution imaging supported increased p50 homodimer presence in the nucleus of BXD2-Il17ra^–⁄– B cells relative to WT BXD2. In vivo injection of AdIL-17 in pre-disease BXD2 mice enhanced anti-IgM induced survival and anergy loss. Surprisingly, despite normal expression of BAFF-R on transitional and mature B cell subsets, BlyS cannot reverse the anergic response of BXD2-Il17ra^–⁄– B cells to BCR stimulation. Analysis of the expression of IL-17RA in the B-cell subsets in BXD2 mice showed that IL17RA is strongly upregulated in transitional T2 (CD93⁺IgM⁺CD23⁺) and germinal center (PNA⁺Fas⁺) B cells. Single cell analysis of T2 B cells revealed the co-expression of Il17ra with B-cell activation gene, Bclxl.

Conclusion: Our results suggest that, in BXD2-Il17ra^–⁄– B cells, the anergy phenotype is established at the transitional stage. In these B cells, stimulus-specific transcription repressive p50/p50 homodimers may act as a master transcriptional regulator to counteract pro-activation/survival NF-ĸB signaling provided by other major B-cell stimulators. Reagents that can promote the NF-ĸB p50/p50 repressome complex may be a novel strategy to enhance B-cell tolerance for autoimmunity. *(Supported by NIH R01AI071110, R01AI083705, P30AR048311, T32 AI007051, VA Merit Review grant 1I01BX000600, Lupus Research Institute, Lupus Foundation of America. Il17ra^–⁄– mice were a generous gift from Amgen).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/il-17-receptor-a-signaling-impedes-nf-kb-p50p50-repressor-and-subverts-b-cell-anergy-in-bxd2-mice/