Increased expression of inducible nitric oxide synthase in nasal epithelial cells in patients with allergic rhinitis

Although ciliated epithelial cells of human nose and paranasal sinuses have recently been reported to be the major source of locally detected nitric oxide (NO), changes to the NO production by these cells and their functional roles remain uncertain in relation to allergic rhinitis. The objective of this study is to investigate differences in the ability of induction of nitric oxide synthase (NOS) isoforms by nasal epithelial cells.

Epithelial cells of the inferior turbinate taken from 12 normal subjects and 12 allergic patients against house dust mite were used. Samples from the house dust group were taken both before and after antigen provocation.

Immunoreactivity for two NOS isoforms, inducible NOS (iNOS) and endothelial NOS (eNOS), was examined by the laser scanning confocal microscope. The labeled cells were processed into digital images, and the fluorescence intensity was assessed quantitatively.

The degree of iNOS expression of the epithelial cells was significantly elevated in the house dust group compared with that of the control group. The expression appeared identical both before and after antigen provocation in the house dust group. On the other hand, there was no significant difference in eNOS expression between the two groups.

We assume that the increased iNOS expression of the epithelial cells in the house dust group might result from stimulated secretion of proinflammatory cytokines during allergic responses. This further suggests profound contribution of nasal epithelial cells to modifying the airway clearance through the production of high levels of NO.