Aryl hydrocarbon receptor in club cells drives Th17-mediated lung injury following inhalation exposure to environmentally persistent free radicals

Environmentally persistent free radicals (EPFRs), generated during thermal combustion processes including hazardous waste remediation, are emerging redox-active pollutants linked to adverse respiratory outcomes. EPFR inhalation induces neutrophilic asthma characterized by substantial lung injury. Neutrophilic asthma is driven by T helper 17 (Th17) cells which secrete IL-17. We identified aryl hydrocarbon receptor (AHR) as a key mediator of EPFR-induced pulmonary Th17 responses. Building on this, we discovered that club cells, specialized airway epithelial cells, are a primary site of AHR activation following EPFR exposure. To dissect the specific role of AHR in club cells, we generated mice with a conditional deletion of Ahr in club cells (AhrΔCC) by crossing Ahr^fx mice [Ahr^tm3.1Bra/J strain] with Scgb1a1-CreER^TM mice [B6N.129S6(Cg)-Scgb1a1^{tm1(cre/ERT)Blh}/J strain]. Littermate (LM; Cre-negative Ahr^fl/fl) control and AhrΔCC mice were exposed to air or EPFRs via inhalation. Flow cytometry and immunofluorescence confirmed loss of AHR in club cells of AhrΔCC mice. As expected, EPFR-exposed LM mice exhibited a pronounced Th17-biased pulmonary immune response accompanied by increased neutrophils in the bronchoalveolar lavage fluid (BALF) compared to air-controls. In contrast, EPFR-exposed AhrΔCC mice failed to induce Th17 responses or neutrophilia. Supporting these findings, BALF analysis showed increased cytokines associated with Th17 signaling and neutrophil recruitment (IL-17, IL-6, IL-1β, KC/GRO) in EPFR-exposed LM mice but not in AhrΔCC mice. Histopathology revealed that EPFR exposure induced airspace enlargement, fibrosis, and mucus hyperproduction in LM mice, whereas AhrΔCC mice were protected. Pulmonary function testing further demonstrated increased airway hyperresponsiveness in EPFR-exposed LM mice which was attenuated in AhrΔCC mice. Collectively, these findings highlight a key epithelial-immune crosstalk in the lung triggered by EPFRs and suggest that AHR signaling in club cells is critical for mediating lung inflammation and functional decline following EPFR exposure. Targeting this pathway may offer a promising therapeutic strategy to prevent or reverse EPFR-induced lung injury.