Metabolic checkpoint AhR prevents pathogenic B cell expansion in murine lupus

Introduction/Rationale: The aryl hydrocarbon receptor (AHR) integrates metabolic and immune cues, but its role in B-cell regulation during lupus remains unclear. We investigated whether AHR restrains pathogenic B-cell development under lupus-mimicking conditions using toll-like receptor 7 (TLR7) stimulation.

Methods: B-cell-specific Ahr knockout (Ahrf/f Cd19.Cre+/- or Ahr B-KO) mice were generated on B6 and lupus-prone BXD2 backgrounds and compared with Ahr B-wild type (Ahr B-WT) controls. TLR7 was activated using R848. AHR was activated using tryptophan (Trp) metabolites 6-formylindolo[3,2-b]carbazole (FICZ) and kynurenine (KYN). B cell subpopulations were determined by flow cytometry. In vitro B cell responses to FICZ were analyzed for transcriptomics using the 10x Chromium single cell RNA-sequencing (scRNA-seq) method while the metabolomics of B cells was analyzed by untargeted LC-MS/MS.

Results: In vivo, FICZ reduced R848-induced T-bet⁺CXCR3⁺ B cells, germinal center B cells, and CXCR3⁺CD138⁺ plasma cells in BXD2 mice. Loss of Ahr in B cells resulted in an increase in R848-induced anti-DNA IgM⁻IgD⁻ and human DN2-equivalents (T-bet⁺FCRL5⁺, T-bet⁺CXCR3⁺) B cells in B6 Ahr B-KO, compared to Ahr B-WT mice. In vitro, AHR activation preserved naïve B cells and blocked their conversion into T-bet⁺CD11c⁺CXCR3⁺ cells, but this protection was absent in BXD2 Ahr B-KO B cells. AHR activation increased KYN- and indole-pyruvic acid (IPyA) derived AHR agonistic ligand metabolites in BXD2 Ahr intact but not Ahr deficient B cells. scRNA-seq confirmed upregulation of IPyA (Il4i1) and KYN (Kynu, Kmo, Haao) catabolic enzyme genes in BXD2 Ahr B-WT but not Ahr B-KO B cells.

Conclusion: These findings identify AHR as a metabolic-immune checkpoint that restrains lupus-related autoantibody production. By uncovering a B-cell intrinsic self-reinforcing pathway that links Trp metabolism to AHR signaling, this work reveals AHR as a promising therapeutic target in lupus and other autoimmune diseases.