Histamine H4 receptor expression is elevated in human nasal polyp tissue.

Altered histamine metabolism is thought to be involved in the pathomechanism of nasal polyposis characterized by local eosinophil infiltration. The present study was performed to determine whether histamine receptors play a role in the effect of histamine in nasal polyp tissue. The findings suggest that the expression of H1 and H4 receptors is elevated in polyp tissue (p=0.045; p<0.001), while the level of H2 and H3 receptors is not increased significantly. The elevation of H1 and H4 receptors' expression may indicate that the histamine related mechanisms are preferentially mediated through H1 and H4 histamine receptors in the polyp tissue. Simultaneously with increased H4 receptor expression, the concentration of eosinophil cationic protein (ECP) was increased significantly in polyp tissue (p=0.002). One may speculate that the H4 receptor mediated histamine effects have a role in eosinophil accumulation and activation in inflammatory diseases of the nasal and paranasal sinus mucosa, such as nasal polyposis.

The pathogenesis of nasal polyposis by immunoglobulin E and interleukin-5 is completed by transforming growth factor-beta1.

OBJECTIVES/HYPOTHESIS: Nasal polyps are benign mucosal protrusions into the nasal cavity of multifactorial origin and are characterized by chronic mucosal inflammation. The suggested multifactorial pathological mechanisms comprise several factors including cytokines and immunoglobulin E (IgE). The study was designed to examine the suggested roles of IgE, interleukin-5 (IL-5), and transforming growth factor-beta1 (TGF-beta1) in the pathogenesis of nasal polyposis. METHODS: Nasal polyps (n = 34) and healthy nasal mucosa samples (n = 9) were taken during routine endonasal surgeries. Immunoglobulin E (n = 13), IL-5 (n = 22), and TGF-beta1 (n = 27) concentrations were measured with enzyme-linked immunosorbent assay technique in homogenized polyp tissue and in control mucosa. Atopic and nonatopic groups were selected and compared. Histomorphological examination and immunohistochemical analysis to detect IL-5 and TGF-beta1 were performed in five specimens. RESULTS: The level of tissue-bound IgE was significantly higher in polyps compared with control specimens and in atopic compared with nonatopic polyps, but between nonatopic polyps and control specimens the difference was not significant. However, significant correlation was found between tissue and serum IgE in the complete polyp (P =.001) and atopic polyps group (P =.05). Tissue IL-5 concentration was significantly higher in polyps compared with control specimens, in which it was below the limit (15 pg/mL), and there was no difference between atopic and nonatopic polyps. In atopic polyps there was significant correlation between tissue IgE and IL-5. Transforming growth factor-beta1 concentration proved to be significantly higher in control mucosa than in polyps, with no difference between atopic and nonatopic polyps. Immunohistochemical analysis revealed numerous IL-5-positive eosinophil cells and TGF-beta1 positivity in the lamina propria of polyp samples, but none in control specimens. CONCLUSIONS: High tissue TGF-beta1 quantity in healthy nasal mucosa without its active form on the cell surface and its low quantity in polyps may reflect its essential role in the inhibitory mechanisms of nasal polyposis. Interleukin-5 plays a key role in the eosinophil recruitment and activation, and both atopic and nonatopic pathways might activate this process. The main sources of IL-5 and TGF-beta1 are the eosinophils and macrophages. Immediate hypersensitivity, besides other mechanisms, might be related to atopic polyps, but the involvement of other, local allergic mechanisms in IgE production of nonatopic polyp tissue cannot be excluded.