Regional expression of epithelial MDR1/P-glycoprotein in chronic rhinosinusitis with and without nasal polyposis.

BACKGROUND: P-glycoprotein (P-gp) is a 170-kDa transmembrane glycoprotein encoded by the MDR1 (ABCB1) gene and is constitutively expressed on lower airway epithelium. P-gp has been shown to function as an immunomodulator regulating efflux of T-helper 1/T-helper 2 (Th1/Th2) cytokines from its host cell; however, its association with sinonasal inflammation has not been described. The purpose of this study is to determine the pattern and degree of epithelial P-gp expression in chronic rhinosinusitis (CRS) with nasal polyposis (CRSwNP) or CRS without nasal polyposis (CRSsNP).

METHODS: Institutional Review Board (IRB)-approved study utilizing sinus, septal, and inferior turbinate mucosa in patients with no disease, CRS, and CRSwNP (n = 4 each). Quantitative fluorescent immunohistochemistry (Q-FIHC) was performed using an anti-P-gp antibody and a secondary fluorescein isothiocyanate (FITC)-conjugated Fc specific fragment. Protein expression was quantified by calculating the epithelial to nonspecific background intensity ratio (4 images/subsite). Scores less than 1 suggested negligible expression. Staining ratios between patient groups and subsites were compared using a 2-tailed Student t test.

RESULTS: Among the sinus mucosa, P-gp expression in CRSwNP (1.570 ± 0.354) was significantly greater than both CRS (1.224 ± 0.248) and control (0.762 ± 0.128) (p < 0.001, p = 0.002; respectively). CRS scores were significantly greater than control (p = 0.002). Among the septal mucosa, there was no significant difference between CRSwNP (0.914 ± 0.264), CRS (1.126 ± 0.476), or control (0.966 ± 0.327). Among the inferior turbinate mucosa, there was no significant difference between CRSwNP (1.047 ± 0.157), CRS (1.099 ± 0.362), or control (0.824 ± 0.181).

CONCLUSION: MDR1/P-gp is overexpressed in the epithelial layer of sinus mucosa in patients with both CRSwNP and CRS relative to other sinonasal subsites. Expression in healthy mucosa is negligible. Given its known immunomodulatory function this suggests that P-gp may play a role in the pathogenesis or maintenance of chronic sinonasal inflammation.