The airway epithelium forms a continuous barrier from the nose to the alveoli and serves a variety of functions. Multiple functionally distinct cell types are involved in these processes. The innate defence functions require a patent airway epithelium, with infections often associated with epithelial defects and phenotypic alterations that are themselves associated with multiple lung diseases. Non-typeable Haemophilus influenzae (NTHi) and respiratory syncytial virus (RSV) are frequently identified in the airways in a range of respiratory diseases These pathogens often trigger exacerbations and worsening symptoms that often result in hospitalisation. This is particularly true in paediatric populations. Although mortality for NTHi and RSV infections alone are themselves low it remains unclear what role these infections play in mortality rates in complex chronic respiratory infections. These studies aimed to establish NTHi and RSV infections within airway epithelium models, and use them as tools to study pulmonary innate defence mechanisms in order to understand the role of these infections in respiratory disease.
In vitro airway models were established using lung derived cell lines, undifferentiated primary human bronchial epithelial (uHBE) cells and air-liquid interface (ALI) differentiated uHBE cell cultures. Following establishment of differentiation we validated ALI cultures using a number of markers, including for the putative innate defence PLUNC family proteins, gel-forming mucins and tubulin. These markers are representative of different epithelial cell types within the cultures. Cultures were infected with NTHi or RSV for periods of time ranging from 1 hour to 7 days with a view to establishing chronic infections and allowing biofilm formation. Monolayer cultures showed an enhanced susceptibility to both infections. Cytokine array profiling showed enhanced pro-inflammatory cytokine profiles in response to NTHi and RSV infections in ALI cells resulting in an ability to manage infections compared to monolayer cultures. Expression analysis indicated that both infections altered the transcription of a number of pro-inflammatory genes. Neutrophil products and trypsin were shown to degrade PLUNC proteins in ALI cell secretions. NTHi also appeared to cause degradation of PLUNC proteins suggesting that infection may impair the innate defence shield of the airway epithelium. Our data showed that differential ALI cultures of human airway cells are a useful model for the study of respiratory pathogens
