Eosinophilic infiltration of the respiratory mucosa is considered an inflammatory hallmark of allergic rhinitis, bronchial asthma and nasal polyposis. However, the mechanisms involved in this infiltration have not yet been totally elucidated. The objective of this study was to investigate and compare the influence of epithelial cell secretions from both nasal polyps (NP) and normal nasal mucosa (NM) on in vitro eosinophil survival. Epithelial cells were identified by microscopy and immunohistochemistry, cultured to confluence, and human epithelial cell conditioned media (HECM) was generated from cultures. Eosinophils were isolated at high viability and purity (> 90%) from peripheral blood and incubated with HECM. HECM from both NM and NP increased eosinophil survival in a dose-dependent manner, this effect being maximal at a concentration of 25% for NM (73.4% +/- 5.5%, n = 26, P < 0.001) and of 10% for NP (74.5% +/- 8.4%, n = 18, P < 0.001). Incubation of monoclonal antibody to human GM-CSF with HECM, neutralized the induction of eosinophil survival by HECM from both NM and NP. HECM from NP contained higher concentrations of GM-CSF (111 +/- 25.4 pg/ml, n = 17) than HECM from NM (97.1 +/- 15.2 pg/ml, n = 8), without reaching statistical significance. Pre-incubation of dexamethasone with eosinophils also blocked HECM-induced eosinophil survival from both NM (10(-8)-10(-5) M; IC50 = 9.5 nM) and NP (10(-7)-10(-5) M; IC50 = 83 nM). These results suggest that: firstly eosinophil infiltration into the respiratory mucosa during allergic reaction and nasal polyposis may be modulated at least in part by GM-CSF from epithelial cells; and secondly epithelial cells from NP might have a more potent effect on inducing eosinophil infiltration of the respiratory mucosa than epithelial cells from NM. Finally, we may consider this as a reliable in vitro model to compare the role of epithelial cells from inflammatory (NP) and non-inflammatory (NM) tissue in respiratory inflammation.
We investigated the effect of budesonide and nedocromil sodium on the secretion of IL-6 and IL-8 by cultured epithelial cells from healthy nasal mucosa and nasal polyps. Human epithelial cell conditioned media was generated with fetal calf serum (FCS) in the presence or absence of budesonide and/or nedocromil sodium. Budesonide inhibited FCS-induced IL-6 and IL-8 release in a dose-dependent manner. The IC25 (25% inhibitory concentration) of budesonide on IL-6 release was higher in nasal polyp than in nasal mucosa epithelial cells (34 nM vs. 200 pM). The IC25 of budesonide on IL-8 release was higher in nasal mucosa than in nasal polyps (145 pM vs. 4 pM). Nedocromil sodium caused a dose-related inhibitory effect on IL-8 release from nasal mucosa (IC25, 207 nM), while it only had a significant effect in nasal polyps at 10(-5) M. Nedocromil sodium had no effect on IL-6 release. The inhibitory effect of budesonide was higher than that of nedocromil sodium on both nasal polyps and nasal mucosa. Budesonide and nedocromil sodium may exert their anti-inflammatory action in the respiratory mucosa by modulating the secretion of IL-6 and IL-8. The different effect of budesonide and nedocromil sodium on IL-6 and IL-8 release may be explained by differences in the mechanisms which regulate the upregulation of these cytokines in inflammatory responses.
These results suggest that topical anti-inflammatory drugs may diminish airway eosinophilic infiltration by decreasing eosinophil viability, that nasal polyp epithelial cell secretions may induce steroid resistance in eosinophils, and that nedocromil sodium has additive effects with steroids.
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