The Role of the Lung Microbiome in COPD
Much has been made of the role of the microbiome in disease. The gut microbiome in particular plays a central role in a number of complex inflammatory disease (including IBD, obesity and probably a number of neurological disorders). The main reason for this being that ~70% of your immune system resides within your gut, and intestinal microflora (your gut microbiome) is necessary for the proper development of your immune system.
The lung microbiome on the other hand is much less well examined. However, a growing number of studies suggest that the lung microbiome plays an important role in chronic obstructive pulmonary disease (COPD). Periods of worsening COPD symptoms are called acute exacerbations and are associated with or caused by bacterial colonization.
What is COPD?
COPD or chronic obstructive pulmonary disease is a progressive disease that makes it difficult to breathe. Progressive means that it gets worse over time.
- COPD is a major cause of disability in the USA.
- COPD is the third leading cause of death in the USA (cardiovascular disease and stroke are number 1 and 2).
- Cigarette smoking is the leading cause of COPD.
- Many cases go undiagnosed.
- COPD has no cure.
There is no cure for COPD, partly because the causes aren’t really known either. Current treatments focus on alleviating symptoms and largely fail to address the underlying cause, so it’s important for scientists to figure out what is causing the disease in order to develop effective treatments.
In a new study published in the European Respiratory Journal (1), an international research team analyzed the lung microbiome of 87 volunteers with COPD when they were stable, undergoing exacerbations (flares in symptoms), at 2 weeks and 6 weeks post-recovery.
The authors not only showed that the microbiome changes during symptom flares, but that the changes were distinct depending on the underlying cause of the symptoms i.e. bacterial or driven by inflammation (caused by white blood cells called eosinophils). Bacterial symptom flares caused an increase in Proteobacteria, while inflammation-derived symptom flares caused an increase in Firmicutes (increases in Firmicutes have been linked to obesity).
In addition to differences in the microbiome of these two flare-up causes, response to treatment usually used during the exacerbations was also different: the bacterial symptom flares responded more to antibiotics and the white blood cell inflammation symptom flares responded better to corticosteroids. Interestingly, corticosteroids have previously been found to affect the lung microbiome (2). The lung microbiota of COPD patients treated with an inhaled corticosteroid and bronchodilator were different from untreated patients showing that the microbiome is not only dependent on the disease but also on the type of medication used.
This study firstly creates a better understanding about what is going on in the lungs of a COPD patient, and secondly suggests that modulation of the microbiome may present a method to modulate the lung inflammatory response.