Methods: Airway epithelial cells obtained from 4 donor lungs were differentiated at air-liquid interface (ALI) and then incubated with recombinant IL-5 for 15 minutes, 1 hour, 6 hours, and 24 hours. Expression of the IL-5R α- and β-subunits was tested using qPCR and Western blot. Following incubation with IL-5 (10 ng/mL), cell lysates were analyzed for phosphorylation of downstream signaling molecules by Western blot.
Results: Expression of the α-subunit of IL-5R was increased 18-fold in differentiated airway epithelial cells compared to undifferentiated monolayers. mRNA expression of the β-subunit was low in unstimulated ALI cells, but increased following incubation for 6 hours with IL-5. Protein expression of the α-subunit was confirmed in both treated and untreated differentiated airway epithelial cells. β-subunit protein expression was low but rapidly inducible by IL-5, suggesting re-localization within the cells. IL-5 stimulation (15-60 min) of ALI cells significantly increased phospho-ERK (mean fold increase=2.7, p=0.003, n=4) and phospho-AKT (mean fold increase=5.2, p=0.029, n=4), but not phospho-STAT5A.
Conclusions: Differentiated human airway epithelial cells express functional IL-5 receptors. The signaling molecules affected suggest that IL-5 may promote epithelial cell growth and proliferation. Collectively, these findings suggest that IL-5 affects airway physiology in asthma in part through effects on airway epithelial cells.