ABSTRACT: Type I interferon (IFN-I, including IFN-? and IFN-?) response has been implicated in eosinophilic inflammation, in addition to antiviral function. This study aimed to investigate the role of IFN-I in the pathogenesis of eosinophilic chronic rhinosinusitis (ECRS). IFN-?, IFN-?, cytokine expression, and IFN-? cellular localization in the sinonasal tissue from control subjects and ECRS patients with nasal polyps (NP) were determined using real time-PCR, ELISA, and immunohistochemistry. ECRS was induced in wild-type (WT) and IFNAR1 knockout (Ifnar1 -/-) mice by intranasal challenge with Aspergillus protease and ovalbumin. Stromal cells cultured from NP tissue were stimulated by exogenous IFN-?, and their CCL11 production and IRF3, IRF7, STAT1, STAT2, and IRF9 gene and/or protein expression were measured. IFN-?, IL-5, IL-13, and CCL11 expression was higher in the NP tissue from ECRS patients, compared to the control group. IFN-? was highly colocalized with the CD11c+ cells in NP. IFN-? levels positively correlated with IL-5, IL-13, and CCL11 levels as well as the number of eosinophils in the NP tissue and CT score. The histological severity of ECRS, levels of IL-4, IL-5, IL-13, and CCL11 in the nasal lavage fluid, and total serum IgE levels were less in Ifnar1 -/- mice than in WT mice. CCL11 production, and STAT1 and STAT2 mRNA and STAT1, phospho-STAT1, and phospho-STAT2 protein expression were significantly increased by exogenous IFN-? in NP stromal cells. Our data suggest that IFN-? response was upregulated in ECRS and may play role in ECRS development. IFN-? may contribute to ECRS by enhancing CCL11 production. Thus, increased IFN-? response in the sinonasal mucosa may underlie ECRS pathogenesis.