The respiratory tract is divided into the upper respiratory tract and the lower respiratory tract - see diagram. The cells lining the respiratory tract (known as epithelial cells) are the body’s first line of defence against the bacteria, viruses, allergens and environmental particles such as dust, which we breathe in. These cells include ones with small ‘hairs’ or cilia on their surface, which beat in a coordinated way to shuttle inhaled particles and mucus out of the airways and other cells which trap inhaled particles and micro-organisms, which are dealt with by the immune system. These cells are tightly joined together to ensure they form an impenetrable barrier.
Recently, with improved molecular techniques, scientists have begun to understand:
• the important role of the cells lining the respiratory tract in the body’s immune response
• the complexity of the lung microbiome – the bacteria, viruses and fungi, which live there – and the role they play in health and disease.
The interaction of these micro-organisms with the epithelial cells, lining the respiratory tract, has been found to be essential for the optimal functioning of the immune system.
This review summarises what is known about how the molecular and cellular mechanisms in the cells lining the respiratory tract interact with the microbiome to shape immunity in the lung. It also discusses the links that exist between the microbiomes of the gut and lung (the so-called ‘gut-lung axis’), their interaction and how they influence each other.
Damage to the lining of the respiratory tract following exposure to infection can result in the onset of inflammation in susceptible individuals and may culminate in lung disease, including pulmonary fibrosis. Changes in the microbiome, resulting in a greater proportion of harmful bacteria and viruses, are also associated with increased incidence of disease and death. Respiratory viruses are also associated with acute exacerbations in IPF.
It is clear we need to understand the lung microbiome better in order to develop:
• markers to predict how a disease is likely to progress so that patients can be given the most appropriate treatments;
• new therapies to target pulmonary fibrosis (and other lung diseases).
This is the main focus of Phil's APF-funded 3-year research project (2019-22).