Murine Eosinophilic and Neutrophilic Chronic Rhinosinusitis Models Reveal Phenotype-Specific Steroid Responses

BackgroundChronic rhinosinusitis (CRS) comprises heterogeneous eosinophilic (type-2) and neutrophilic (type-1/3) endotypes, yet existing murine models rarely distinguish them or compare their therapeutic responsiveness.MethodsSeven-week-old female C57BL/6N mice received intranasal instillations three times weekly for 4 or 12 weeks with either (1) a clinically relevant airborne allergen cocktail (house dust mite [HDM], Aspergillus fumigatus, Alternaria alternata, and Staphylococcus aureus protease) to induce eosinophilic CRS (ECRS) or (2) an innate stimulus mixture (lipopolysaccharide, β-1,3-glucan, and S. aureus protease) to induce neutrophilic CRS (NCRS). A parallel cohort received weekly dexamethasone administration (2 mg/kg). Endpoints included flow cytometry, enzyme-linked immunosorbent assays, quantitative PCR, histology, and immunofluorescence assays.ResultsFour-week allergen exposure produced a pure ECRS phenotype characterized by robust tissue eosinophilia, type-2 cytokines, and marked responsiveness to dexamethasone. Extending allergen delivery to 12 weeks generated mixed CRS with superimposed neutrophilia, upregulation of Il1b/Tgfb1, mucus hypersecretion, and attenuated steroid efficacy. Innate stimulus treatment yielded a steroid-resistant NCRS phenotype dominated by neutrophils, elevated Ifng/Il17a expression, and minimal type-2 biomarkers. Systemic eotaxin and HDM-specific immunoglobulin E mirrored those found in local eosinophilia, whereas circulating granulocytes remained unchanged across groups.ConclusionsBy adjusting the stimulus type and duration, we established tunable murine models that recapitulate pure ECRS, mixed CRS, and steroid-resistant NCRS within a single genetic background. These paired models provide a versatile platform for dissecting endotype-specific mechanisms and evaluating tailored interventions, highlighting the potential importance of early, phenotype-directed CRS therapy.