Expression of nitric oxide synthases in nasal mucosa from a mouse model of allergic rhinitis

Nitric oxide (NO), which is produced by nitric oxide synthase (NOS), has been recently identified as a multifunctional mediator. As for nasal tissue, however, the distribution and expression patterns of 3 isoforms of NOS, including neuronal NOS (nNOS, type I NOS), inducible NOS (iNOS, type II NOS), and endothelial NOS (eNOS, type III NOS), are still unclear. To evaluate the function of NO in the pathophysiology of nasal allergy, we investigated the distribution of NOSs in the nasal mucosa of C57BL/6 mice with allergic rhinitis to the house dust mite, Dermatophagoides farinae. Immunoreactivity to each isoform of NOS was immunohistochemically observed. In the allergic nasal mucosa, many eosinophils had infiltrated. Immunoreactivity to NOS types I and III was localized to the surface epithelial and vascular endothelial cells in both allergic and control groups without a statistically significant difference. In contrast, the type II NOS immunoreactivity was weak in normal mice and increased after allergic sensitization. The type II NOS expression of the surface epithelial and vascular endothelial cells was significantly elevated in the allergic group as compared with the control group. These findings suggest that a large amount of NO may be produced in the nasal mucosa of mice by type II NOS after allergic sensitization and that type II NOS may play an important role in the pathogenesis of allergic rhinitis.