Stabilization of MHCII on dendritic cells via AhR-mediated blockade of proteasomal degradation drives Th17 responses to exogenous antigens.

BACKGROUND

Dendritic cells (DCs) activate CD4+ T cells by presenting antigens via MHCII. MHCII surface levels are regulated by diverse mechanisms, including ubiquitination. The aryl hydrocarbon receptor (AhR) further modulates MHCII expression and DC function. Whether monocyte-derived dendritic cells (mo-DCs) regulate antigen presentation by sensing exogenous antigens through the AhR remains unclear.

METHODS

Human THP1-DCs or murine BMDCs were treated with exogenous antigens, AhR antagonist CH223191, shRNA knockdown (AhR/IL4I1/CD83), AhR overexpression, or inhibitor (MG132/chloroquine/NH4Cl). Assessments included flow cytometry (MHCII/CD83/CD86), DC-T co-cultures (Th17 differentiation), qPCR, immunoblotting, tryptophan metabolite profiling (LC-MS/MS) and ELISA. In vivo, rPEA-exposed C57BL/6 mice received intratracheal CH223191, with analysis of lung DCs, IL-17A+ cells, BALF, and histopathology.

RESULTS

Exogenous antigens (rPEA, OVA, Bet v 1) activated the AhR pathway in mo-DCs, upregulating AhR and downstream target genes (CYP1A1, AHRR). AhR regulates MHCII (HLA-DR) and CD86 membrane expression, with HLA-DR more affected. Antigen stimulation triggered tryptophan metabolism to produce AhR ligands, such as the metabolite indole-3-lactic acid produced by IL4I1. AhR activation sustained elevated surface HLA-DR by blocking proteasome-dependent degradation-independent of the newly synthesized MHCII-partially via CD83. AhR inhibition impaired mo-DC antigen presentation to CD4+ T cells and blocked Th17 differentiation in vitro. In mice, CH223191 attenuated rPEA-induced lung inflammation, reducing immune cell infiltration, IL-17A+ cells, and MHCII on CD11b+CD103- DCs in lymph nodes.

CONCLUSIONS

Exogenous antigens induce DC tryptophan metabolism, elevating AhR ligands. Activated AhR upregulates CD83 and blocks proteasomal degradation, sustaining the surface MHCII to drive Th17 responses. AhR inhibition modulates DC-mediated immunity and suppresses inflammatory pathology.