IL4I1 and chronic rhinosinusitis without nasal polyps: Furthermore, protein levels of IL4I1, AhR, and CYP1B1 were consistently upregulated in CRSwNP and CRSsNP compared with control, and the protein expression of IL4I1, AhR, and CYP1B1 was significantly higher in the CRS + PM2.5 group compared with the CRS group alone.