Background/Purpose: Systemic lupus erythematosus (SLE) is a predominantly female autoimmune disease, with a 9:1 female-to-male ratio. Our previous studies indicated that increased T-bet+ age-related B cells (ABCs) was associated with elevated circulating type I interferon (IFN) and autoantibody development in female, but not male, lupus prone BXD2 mice. While dysregulated type I IFN signaling and Toll-like receptor 7 (TLR7) activation are established contributors to SLE, the molecular mechanisms underlying sex-specific immune responses in mice and humans are not fully understood.

Methods: The transcriptomic profiles of naïve B cells (IGHM+IGHD+IGHG-) from 11 female (5 SLE patients and 6 healthy) and 11 male donors (4 autoimmune inflammatory disease patients [AID] and 7 healthy) were analyzed by single cell-RNA sequencing analysis. B-cell response induced by R848 (TLR7 agonist) plus IFNβ in vitro was analyzed for early activation of CD69 at 4h and T-bet at 24h, respectively, using B cells derived from female and male BXD2 mice. Real-time PCR was used to determine if R848 plus IFNβ impacts the expression of mitochondrial electron transport chain (ETC) complex I genes, Ndufa1 and Ndufa3. Mitochondrial oxidative phosphorylation (OxPhos) was measured using the Mitochondrial Stress Test and Seahorse Analyzer at 48 and 72h. Flow cytometry was used to evaluate the impact of the complex I inhibitor IM-156 on R848 plus IFNβ-induced T-bet and GL7 upregulation at 72h.

Results: Increased IFN-stimulated genes was the primary transcriptomic signature in female SLE patient B cells. B cells from females, regardless of health status and ethnicity, exhibited elevated expression of mitochondrial ETC genes, including complex I genes compared to males. Regarding mice, there was similar early activation of CD69 at 4h and T-bet expression at 24h in B cells from both sexes. However, B cells from female mice exhibited significantly higher expression of Ndufa1 and Ndufa3 at 24h and 72h. There was a significant increase in basal and maximal respiration, ATP production, and reserve capacity in B cells from female mice at 48h and 72h. This was associated with significantly increased development of T-bet+GL7+ B cells in female mice at 72h. In vitro pharmacologic inhibition of complex I with IM-156 significantly attenuated T-bet upregulation in B cells of female mice.

Conclusion: These findings suggest that the development of T-bet⁺ B cells in female BXD2 mice is strongly dependent on increased mitochondrial OxPhos. Sex-biased differences in OxPhos may therefore act as an intrinsic factor, making it more likely for precursor B cells to reach the energy thresholds needed for differentiation into ABCs under TLR7 and type I IFN stimulation in females with lupus.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/enhanced-mitochondrial-activity-in-b-cells-from-females-is-required-to-drive-increased-t-bet-induction-by-tlr7-in-lupus/