BackgroundIn a gene expression analysis comparing sinus mucosa from allergic fungal rhinosinusitis (AFRS) to that from non-AFRS chronic rhinosinusitis with nasal polyp (CRSwNP) subjects, the antimicrobial peptide (AMP), histatin 1 (HTN1), was found to be the most differentially down-regulated gene in AFRS. ObjectiveTo identify the molecular etiology of the down regulated expression of HTN1 MethodsWe used RT-PCR to compare the expression of AMPs and utilized a fungistasis assay to evaluate the anti-fungal activity of sinus secretions. Using flow cytometry, we characterized the presence of Th17/22 cells and STAT signaling from AFRS, non-AFRS CRSwNP patients, and healthy controls. ResultsWe confirm the decreased expression of AMPs in AFRS sinus mucosa with concordant decrease in antifungal activity in sinus secretions. We show that IL-22 and IL-22-producing T cells are deficient within sinus mucosa of AFRS subjects. In vitro studies demonstrated a defect in IL-6/STAT3 signaling critical for TH17/TH22 differentiation. Epithelial cells from AFRS patients could express AMPs when stimulated with exogenous IL-22/IL-17 and circulating Th17 cell abundance was normal. ConclusionSimilar to other hyper-IgE syndromes, but distinct from CRSwNP, AFRS patients express a defect in STAT3 activation limited to IL-6-dependent STAT3 phosphorylation that is critical for Th17/TH22 differentiation. This defect leads to a local deficiency of IL-17/IL-22 cytokines and deficient AMP expression within diseased sinus mucosa of AFRS patients. Our findings support evaluation of therapeutic approaches that enhance airway AMP production in AFRS.