Your lungs are not sterile and have their own microbiota

While we know a lot about the gut and its microbiome, the lung microbiome remains a mystery for most of us. For a long time, scientists believed that the lungs lacked microbial life. In fact, the lung mucosa hosts a variety of bacteria, fungi, and viruses, though fewer in number compared to the gut microbiota. “The respiratory microbiome is perpetually renewed and dynamic due to respiration and mucosal movements,” explained Dr. Gregory Bouchaud, an immunologist at INRAE and expert in the lung microbiome.

As it turns out, science is revealing the unique ways your lung microbiota can affect your health. Its microbial community is vital for respiratory health, helping to regulate immune responses and defend against harmful pathogens. “The lung microbiota is acquired throughout the first two years of life, after which it gains resilience, providing therefore a barrier against pathogens,” stated Dr. Bouchaud.

It was traditionally believed that the respiratory system was separate from the digestive system. However, emerging research has revealed a complex communication network between the gut and lungs, known as the gut-lung axis. Simply put, this two-way communication means that the intestine influences the lungs and vice versa. For instance, viral lung infections can impact the gut microbiota. “Patients suffering from viral lung infections, such as influenza (flu), often exhibit gastrointestinal symptoms,” noted Dr. Bouchaud. This crosstalk underscores the importance of considering both the lungs and the gut when addressing respiratory illnesses. Likewise, a healthy gut microbiota ensures that immune cells in the lungs work well to keep respiratory infections at bay.

 

How are the lungs and gut connected?

The gut and lungs are intricately linked through the immune system. When the gut detects harmful pathogens, it activates immune responses to combat them. “The lung microbiome communicates with the gut and vice versa, through bacterial components and metabolites that travel through the bloodstream to influence the immune system preparing it to fight off potential threats, ” explained Dr. Bouchaud.

Conversely, imbalances in the composition of the gut microbiota can lead to a damaged gut lining, allowing pathogens to exit the gut, enter the bloodstream and trigger dysregulated immune responses in distant parts of the body, increasing the lungs’ susceptibility to infections and inflammatory conditions. “Scientists use animals without microorganisms (germ-free) to prove that in the absence of a pulmonary microbiome, they are more susceptible to respiratory diseases,” said Dr. Bouchaud. Disruptions to the gut microbiota composition, such as those caused by antibiotics, diet, or stress, can impact the balance of the immune function and contribute to respiratory diseases. “During COVID-19, researchers found that people with severe infections had a dysbiotic lung microbiome. In addition, in lung cancer, scientists use the lung microbiome to predict patient reactions to immunotherapy,” added Dr. Bouchaud.

 

What is the link between the gut microbiota and respiratory diseases?

While acute inflammation (response of your immune system to fight pathogens) is a necessary response to infections; chronic inflammation can have detrimental effects on lung function triggering the development and progression of diseases. An altered lung microbiota is associated with respiratory disease progression, but whether it is causally involved in disease onset and its relevance for managing symptoms remains to be studied:

  • Asthma: is a chronic inflammatory disorder characterized by airway inflammation with respiratory symptoms such as wheezing and shortness of breath. Emerging evidence suggests that disturbances to the gut microbiota composition during early life, through C-section, antibiotic use or an extremely clean environment (hygiene hypothesis) could increase the risk of asthma in adulthood. “Interestingly, patients with varying asthma severity show distinct lung microbiome signatures, but we don’t know if this is the cause or the consequence,” Dr. Bouchaud noted.
  • Chronic Obstructive Pulmonary Disease (COPD): is characterized by airflow limitation and respiratory symptoms. While smoking is a primary risk factor for COPD, emerging research indicates that dysbiosis of the gut microbiota may contribute to disease progression and exacerbation.
  • Cystic Fibrosis (CF): involves the excessive accumulation of scar tissue in the lungs, leading to impaired gas exchange and respiratory function. While the exact causes of fibrosis remain elusive, dysregulated immune responses and chronic inflammation are thought to play significant roles. In addition, patients with CF present a distinct gut microbiota compared to healthy controls.

 

What is the future of this field?

Advances in microbiome research offer exciting possibilities for disease prevention through targeted interventions, using prebiotics or probiotics. Prebiotics and dietary fiber are known to influence the gut microbiome and promote the release of beneficial metabolites regulating overall inflammation. “Probiotics could be a promising avenue, but more research needs to be done to determine their impact on respiratory health. We are not there just yet,” Dr. Bouchaud stated.

Lifestyle factors such as diet, exercise, stress management, and smoking cessation can profoundly influence the gut microbiota and immune function, thereby impacting respiratory outcomes. “We should eat a healthy diet rich in fruit and vegetables that contain antioxidants, fiber, and other beneficial components rather than relying on dietary supplements alone,” suggested Dr. Bouchaud. “Tobacco and stress change the pH, temperature, and humidity of the lungs, making them more likely to be colonized by opportunistic pathogens,” he warned. By addressing modifiable risk factors and promoting a healthy environment, individuals can take proactive steps toward improving their lung health and overall well-being.

The recently discovered gut-lung axis represents a new field of research, shedding light on the complex interaction between gut microbiota and respiratory health. By dispelling myths and exploring potential interventions, we can pave the way for innovative strategies to prevent and manage respiratory disease. “We are taking a holistic approach, with immunologists and microbiologists working together to examine the immune function and microbiome. Our focus is on the stages of life when the lung microbiome is most susceptible to change (from pregnancy to two years old), in order to establish the right trajectory,” said Dr. Bouchaud.

 

 

References:

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