Expression of NMU and NMUR1 in tryptase-positive mast cells and PBLs in allergic rhinitis patients’ nasal mucosa

Background The neuropeptide U (NMU) has been proven to elicit the release of mediators from mast cells (MCs) through its receptor NMUR1 in allergic inflammatory models. However, little is known about the correlations between NMU and MCs in human allergic rhinitis (AR). Objective The objective of this study is to investigate the expressions of NMU and NMUR1 in the tryptase + MCs and the peripheral blood leukocytes (PBLs) in human nasal mucosa with AR. Methods Specimens of nasal mucosa from patients with AR (n = 10) and control patients without AR (n = 8) were collected and soaked in frozen tissue liquid solution (OCT) in tum. Cryostat sections were prepared for immunofluorescence staining. Tryptase was used as a marker to detect mast cells and other tryptase + immune cells. The expression of NMU and NMUR1 was respectively determined by double staining using a confocal microscope. Results Neither NMU nor NMUR1 were detected in the tryptase + mast cells in the human nasal mucosa. To our surprise, both NMU and NMUR1 were co-expressed with tryptase in the PBLs within peripheral blood vessels in AR and controls. Conclusion Our findings showed that NMU could not influence human nasal tryptase + mast cells directly through NMUR1 in AR. The co-expression of both NMU and NMUR1 with tryptase in the PBLs provided new insight into the potential roles of NMU and tryptase in the circulation PBLs, and the infiltrated PBLs may promote nasal allergic inflammation by producing tryptase and NMU.