Introduction
The nasal epithelium represents the point of first contact between the respiratory system and the external environment. The nasal epithelium is comprised of goblet, basal and ciliated cells, which are essential in establishing mucociliary clearance, producing anti-microbial peptides, chemokines and cytokines, and forming a protective barrier. The normal respiratory epithelium has the ability to remodel and repair its integrity after epithelial damage 1,2. Persistent asthma is associated with epithelial dysfunction, associated with a disturbance of the normal ability to repair wounds 3. Studies using primary bronchial epithelial cells, obtained from children with atopy and/or “asthma” and grown in submerged, monolayer cultures, suggest an inability to heal wounds (reviewed in 4). While these results are consistent with observations from bronchial biopsies in adults with persistent asthma 3, submerged, monolayer cultures do not adequately represent the conditions seen in a fully differentiated pseudostratified epithelium in vivo 5. To minimize these deficiencies primary airway epithelial cells can be grown at the air-liquid interface (ALI) into a fully differentiated pseudostratified epithelium consisting of basal, goblet and ciliated cells 6.
Respiratory viral infections are involved in the induction and progression of asthma 7,8. Wheezing and asthma exacerbation, especially in children and the elderly, are often associated with respiratory infections due to respiratory viruses such as respiratory syncytial virus (RSV) and human rhinovirus infection9,10. Debate exists about whether the asthmatic respiratory epithelium has an exaggerated response to respiratory viral infections but evidence from in vivo and ex vivo studies show a different pattern of cytokine secretion from “asthmatic” epithelial cells under baseline and stimulated conditions1,11. Certainly, the inflammatory milieu differs in the “asthmatic” airway when compared to that in healthy individuals3. How this milieu influences wound healing is little studied.
We have recently developed an ex vivo model for assessing wound healing in a well-differentiated epithelium, grown at the air-liquid interface (ALI), using primary nasal epithelial cells (NECs)6. The aim of the present study was to use our model to determine: a) the ability of a nasal epithelium, grown in ALI culture, from cells obtained from subjects with asthma and/or atopy, to heal a wound, and b) to determine the influence of the “asthmatic” airway milieu on wound healing. We chose to use primary NECs obtained from adults to avoid the uncertainties in asthma diagnosis in children.
Methods ( full details can be found in the online supplement)