Abstract
IntroductionThe epithelial and endothelial barriers of the airway mucosa are critical for regulation of tissue homeostasis and protection against pathogens or other tissue damaging agents. In response to a viral infection, epithelial cells must signal to the endothelium to initiate immune cell recruitment. This is a highly temporal regulated process; however, the mechanisms of this cross‐talk are not fully understood.MethodsIn a close‐contact co‐culture model of human airway epithelial and endothelial cells, cellular crosstalk was analyzed using transepithelial electrical resistance (TER) measurements, immunofluorescence, electron microscopy, and ELISA. Viral infections were simulated by exposing airway epithelial cells apically to double‐stranded RNA (Poly(I:C)). Using a microfluidic culture system, the temporal release of mediators was analyzed in the co‐culture model.ResultsWithin 4 h of challenge, double‐stranded RNA induced the release of TNF‐α by epithelial cells. This activated endothelial cells by triggering the release of the chemoattractant CX3CL1 (fractalkine) by 8 h post‐challenge and expression of adhesion molecules E‐selectin and ICAM‐1. These responses were significantly reduced by neutralising TNF‐α.ConclusionBy facilitating kinetic profiling, the microfluidic co‐culture system has enabled identification of a key signaling mechanism between the epithelial and endothelial barriers. Better understanding of cell–cell cross‐talk and its regulatory mechanisms has the potential to identify new therapeutic strategies to control airway inflammation.
Highlights
The epithelial and endothelial barriers of the airway mucosa are critical for regulation of tissue homeostasis and protection against pathogens or other tissue damaging agents
The close proximity of the epithelial and endothelial cells in the co-culture model was important for the observed decrease in ionic permeability in the co-cultures, since culturing the endothelial cells at the bottom of the culture plate rather than directly on the basolateral side of the permeable filter support resulted in a smaller increase in transepithelial electrical resistance (TER) (Fig. 2B)
We demonstrated that cellular crosstalk plays an important role in co-ordinating barrier functions of the airway epithelium and endothelium
Summary
The epithelial and endothelial barriers of the airway mucosa are critical for regulation of tissue homeostasis and protection against pathogens or other tissue damaging agents. In response to a viral infection, epithelial cells must signal to the endothelium to initiate immune cell recruitment This is a highly temporal regulated process; the mechanisms of this cross-talk are not fully understood. Results: Within 4 h of challenge, double-stranded RNA induced the release of TNF-a by epithelial cells This activated endothelial cells by triggering the release of the chemoattractant CX3CL1 (fractalkine) by 8 h post-challenge and expression of adhesion molecules E-selectin and ICAM-1. As well as contributing to tissue homeostasis through its barrier functions, the airway epithelium must be able to respond appropriately when it is compromised by signaling to cells of the innate and adaptive immune system [3] These immune cells may reside locally, or be recruited from the circulation via endothelial cell activation. The integrated responses arising from this cell–cell communication can be observed readily in animal models in vivo, in vitro models using human cells are more amenable for dissection of mechanisms of cell–cell communication and identification of key cell-type specific mediators with relevance to human disease [4]
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