Abstract
Background The mechanisms underlying mucosal eosinophilia in chronic rhinosinusitis with nasal polyps (CRSwNP) remain poorly clarified. The nervous system and neuropeptides play an important role in the regulation of immune response. Herein we explore the expression and function of hemokinin-1 (HK-1), a newly identified tachykinin, along with its receptor neurokinin 1 receptor (NK1R) in CRSwNP. Methods HK-1, NK1R, and C-C motif chemokine ligand 24 (CCL24) expression in nasal tissues (53 eosinophilic CRSwNP, 32 non-eosinophilic CRSwNP, and 33 controls) was investigated by quantitative reverse transcript polymerase chain reaction (RT-PCR) and immunofluorescence staining. THP-1, a human monocytic leukemia cell line, and eosinophilic polyp tissues were stimulated with HK-1. Cells, tissues, and culture supernatants were subsequently collected for detection of the production of various inflammatory cytokines and chemokines by quantitative RT-PCR and enzyme-linked immunoassay. Results HK-1 and NK1R mRNA and protein expression were upregulated in eosinophilic and non-eosinophilic nasal polyps compared with control tissues, with eosinophilic polyps demonstrating a higher upregulation compared with that of non-eosinophilic polyps. Eosinophils constituted the major source of HK-1, whereas macrophages were the predominant cell type exhibiting NK1R in eosinophilic polyps. HK-1 induced CCL24 production from macrophages differentiated from THP-1 cells; this was abolished by an NK1R antagonist. HK-1 also induced CCL24 production from ex vivo-cultured eosinophilic nasal polyps. CCL24 was expressed by macrophages in eosinophilic but not non-eosinophilic polyps. The expression level of HK-1 correlated with CCL24 expression and tissue eosinophilia in eosinophilic nasal polyps. Conclusion Eosinophil-derived HK-1 induces CCL24 production from macrophages and therefore exaggerates eosinophilic inflammation in CRSwNP.