Effect of seasonal allergen exposure on mucosal IL-16 and CD4+cells in patients with allergic rhinitis

Background: CD4+ T cells constitute a major source of cytokines in allergic diseases such as allergic rhinitis. Interleukin (IL)-16 selectively recrui ts CD4+ cells. Methods: We evaluated the effect of natural allergen exposure during a gras s-pollen season on IL-16 expression and nun-liber of CD4+ cells in nasal mu cosa. Patients with allergic rhinitis (n = 16) were treated with either a n asal glucocorticoid beclomethasone (BDP; 400 mug/day) or placebo, and gave nasal biopsies prior to and during the grass-pollen season. The evaluated m arkers in allergic rhinitis patients were also compared to those in healthy control subjects (n = 5). Results: Prior to the pollen season, the expression of IL-16, but not the n umber of CD4+ cells, was significantly higher in patients with allergic rhi nitis than in healthy control subjects. The grass-pollen season further inc reased IL-16 expression and also increased the number of CD4+ cells in plac ebo-treated, but not in BDP-treated, allergic rhinitis patients. The pollen -season-induced change in IL-16 expression and in CD4+ cells was significan tly more pronounced in placebo- than in BDP-treated patients. There was a s ignificant correlation between the change in IL-16 expression and the numbe r of CD4+ cells. Conclusions: These data suggest that local upregulation of IL-16 expression contributes to the inflammation observed in seasonal allergic rhinitis. Hy pothetically, inhibition of IL-16 expression can be one of several mechanis ms by which nasal glucocorticoids achieve their anti-inflammatory effect in allergic rhinitis.