Abstract
The airway epithelium forms a barrier against infection but also produces antimicrobial peptides (AMPs) and other inflammatory mediators to activate the immune system. It has been shown that in allergic disorders, Th2 cytokines may hamper the antimicrobial activity of the epithelium. However, the presence of Th2 cytokines also affects the composition of the epithelial layer which may alter its function. Therefore, we investigated whether exposure of human primary bronchial epithelial cells (PBEC) to Th2 cytokines during mucociliary differentiation affects expression of the human cathelicidin antimicrobial protein (hCAP18)/LL-37 and human beta defensins (hBD), and antimicrobial activity.PBEC were cultured at an air-liquid interface (ALI) for two weeks in the presence of various concentrations of IL-4 or IL-13. Changes in differentiation and in expression of various AMPs and the antimicrobial proteinase inhibitors secretory leukocyte protease inhibitor (SLPI) and elafin were investigated as well as antimicrobial activity.IL-4 and IL-13 increased mRNA expression of hCAP18/LL-37 and hBD-2. Dot blot analysis also showed an increase in hCAP18/LL-37 protein in apical washes of IL-4-treated ALI cultures, whereas Western Blot analysis showed expression of a protein of approximately 4.5 kDa in basal medium of IL-4-treated cultures. Using sandwich ELISA we found that also hBD-2 in apical washes was increased by both IL-4 and IL-13. SLPI and elafin levels were not affected by IL-4 or IL-13 at the mRNA or protein level. Apical wash obtained from IL-4- and IL-13-treated cultures displayed increased antimicrobial activity against Pseudomonas aeruginosa compared to medium-treated cultures. In addition, differentiation in the presence of Th2 cytokines resulted in increased MUC5AC production as has been shown previously.These data suggest that prolonged exposure to Th2 cytokines during mucociliary differentiation contributes to antimicrobial defence by increasing the expression and release of selected antimicrobial peptides and mucus.
Highlights
The airway epithelium is a pseudostratified columnar epithelium containing basal, secretory and ciliated cells
Two-week exposure of differentiating bronchial epithelial cells to IL-4 or IL-13 enhances hCAP18/LL-37 and human beta defensins (hBD)-2 mRNA expression as well as hCAP18/LL-37 protein release To study how exposure to IL-4 or IL-13 during differentiation of bronchial epithelial cells affects expression of antimicrobial peptides, we exposed primary bronchial epithelial cells (PBEC) that were cultured at the air-liquid interface (ALI) to various concentrations of these cytokines for 14 days to induce differentiation
Using SDSPAGE and Western Blot analysis, we show that concentrated basal medium of ALI cultures treated with IL-4 contain a protein of approximately 4.5 kDa (Figure 2C), suggesting that hCAP18 is cleaved into a smaller fragment which could either be LL-37 or other peptides known to be cleaved from hCAP18 [24]. hBD-2 protein level in apical washes was increased by both IL-4 and IL-13 (Figure 2D), whereas in basal medium it was not. hBD-3 protein release into apical washes as measured by ELISA was variable: it was undetectable in cultures from two out of six donors; IL-4 induced hBD-3 protein release in cultures of two donors, whereas it decreased hBD-3 protein release in cultures of two other donors
Summary
The airway epithelium is a pseudostratified columnar epithelium containing basal, secretory and ciliated cells. This layer constantly regenerates through migration, proliferation and differentiation of epithelial cells to form a barrier to protect against inhaled pathogens. Various studies including our own [9] have indicated that Th2 cytokines are able to influence the phenotype of the airway epithelium. It was shown that IL-4 can drive differentiation of cultured human airway epithelial cells towards a mucus hypersecretory phenotype [13]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
