The small airways are known as ‘the silent region’ of the lung as pathology in this area often goes undetected by currently available tests. This deficiency has deadly consequences for patients with lung transplants as it is the obliteration of the small airways by scarring as a result of chronic, untreated rejection that eventually leads to the loss of the allograft.

We have developed a safe and simple method of reliably sampling the small airway epithelium during post-transplant bronchoscopy. By combining this technique with our established practice for evaluating epithelium using multiparameter flow cytometry we are able to gain unprecedented insight into the inflammatory processes, both alloimmune (eg. CD8⁺CD103⁺GB⁺) and tolerising (eg. CD4⁺CD25⁺CD127^lowFoxp3⁺), which determine patient outcomes after transplantation.

In the clinic, we anticipate that this exciting advance will allow clinicians to identify the patient whose allograft is at risk and allow timely intervention, as well as allowing better titration of immunosuppression in patients with a healthy allograft in order to minimise the side-effects of immunosuppression. In the lab, it will provide valuable insight into the relationships between the innate and adaptive immune systems and the epithelium, not only in the setting of transplantation, but also, for the first time, in healthy humans. We anticipate that our findings will have implications for the understanding of transplantation immunology in other epithelialized allografts, and that the techniques we describe will be applied to the study of other lung diseases, such as chronic obstructive pulmonary disease and asthma.