IL-5 synthesis is upregulated in human nasal polyp tissue

Background: In most nasal polyps, tissue eosinophilia is a striking finding, the pathologic mechanism of which is not understood. Objective: This study was performed to investigate a possibly distinct cytokine and chemokine pattern that could explain the characteristic tissue eosinophilia in nasal polyps. Methods: Polyps from 23 patients and turbinate tissue from 18 control subjects were investigated. The cytokine protein content (IL-1 beta, IL-3, IL-4, IL-5, IL-6, IL-8, IL-10, tumor necrosis factor-alpha, granulocyte-macrophage colony-stimulating factor, IL-IRA, RANTES, GRO-alpha) of tissue homogenates was measured by ELISA. Immunohistochemistry was performed in selected samples to detect IL-5(+), major basic protein-positive, and EG2(+) cells. Results: IL-5 was detectable in only one sample of tissue from 18 control subjects but was found in 18 of 23 nasal polyps. Immunohistochemistry revealed an abundant number of IL-5(+) cells, of which 69.5% could be identified as eosinophils by morphology. IL-6, IL-8, IL-10, tumor necrosis factor-alpha, GRO-alpha, and RANTES were detected in all specimens, without significant differences between groups (p greater than or equal to 0.05), whereas significantly higher concentrations of IL-1 beta and IL-1RA were found in turbinate mucosa (p < 0.05). IL-3 was not detectable; granulocyte-macrophage colony-stimulating factor could only occasionally be found. Conclusion: This study indicates that IL-5 plays a keg role in the pathophysiology of eosinophilic nasal polyps and may be produced by eosinophils.