Macrophage-mediated activation of the IL4I1/AhR axis is a key player in allergic rhinitis

Epidemiological evidence suggests that environmental pollutants precipitate the occurrence of allergic rhinitis (AR). The aryl hydrocarbon receptor (AhR), a receptor or sensor for various contaminants, is closely related to immunomodulation and the polarization of M2 macrophages. However, the mechanisms involving AhR and M2 macrophages in AR remain unclear.

Bioinformatics analysis of GEO datasets (GSE180697 and GSE180697) assessed AhR and IL4I1 expression levels, which were then verified in the nasal mucosa, monocytes and serum of patients with AR using western blotting, quantitative real-time polymerase chain reaction (qRT-PCR), immunofluorescence, and enzyme-linked immunosorbent assay (ELISA). Primary human mononuclear cells were isolated from peripheral blood using a magnetic separation technique, and THP-1 cell lines with IL4I1 overexpression or downexpression were established through lentiviral constructs. M2 macrophages were induced with the cytokines CSF, IL4 and IL13 and then treated with the AhR agonist FICZ or inhibitor CH223191. The polarization of M2 macrophages was measured by flow cytometry and western blotting. Furthermore, primary nasal epithelial cells and macrophages were co-cultured to assess the epithelial-mesenchymal transition (EMT) in epithelial cells. The AR murine model was established using ovalbumin (OVA). Inflammation within the nasal mucosa and lung tissue was examined after CH223191 or IL4I1 treatment.

Nuclear translocation of AhR and upregulation of IL4I1 was observed in peripheral mononuclear cells and nasal mucosal tissue of patients with AR. Through the activation of AhR, IL4I1 promoted M2 macrophage polarization. Furthermore, modulation of the IL4I1/AhR axis regulated the migratory impact of OVA on T-M2 cells. The IL4I1/AhR axis was involved in the regulation of M2 macrophage-associated EMT and contributed to the expression of IL-33 and STAT6 phosphorylation in epithelial cells. In AR mice, increased AhR nuclear translocation and higher expression of IL4I1 and the M2 macrophage marker CD206 in the lungs was observed. The IL4I1/AhR axis exacerbated allergic symptoms in AR mice, fostering allergic inflammation within the nasal mucosa and lungs.

The IL4I1/AhR axis is activated within the mononuclear phagocyte system of patients with AR. This activation facilitates the polarization of mononuclear cells into M2 macrophages, which further aggravates EMT in epithelial cells and exacerbates inflammation in AR. This study may provide novel strategies for the precise treatment of AR.