Lung Microbiome - Everything You Need to Know

Introduction

The lung microbiota is diverse. However, the microbes are less in the lungs compared to the gastrointestinal tract. The lung microbiome is present in healthy individuals and those with respiratory disorders. They prevent diseases by influencing the susceptibility to pathogens, but the microbiota also gets affected by diseases. The lung microbiome has a major impact on respiratory diseases and infections. They interact with the host and the pathogen to regulate immune homeostasis.

What Is Lung Microbiome?

The lung microbiota is the community of bacteria, fungi, viruses, and bacteriophages in the lungs. Bacterial species include Prevotella, Sphingomonas, Pseudomonas, Acinetobacter, Fusobacterium, Megasphaera, Veillonella, Staphylococcus, and Streptococcus. Fungi commonly seen are Candida, Malassezia, Saccharomyces, and Aspergillus.

How Does the Lung Microbiome Effects Lungs?

The lung microbiome interacts with lung immune cells and identifies pathogens. They induce these cells to produce inflammatory cytokines to destroy the pathogens. This initiates innate immune responses. The immune cells discriminate the difference in signals between good and bad bacteria and destroy only the bad bacteria. The lung microbiota cannot cross the mucosal layer and cannot be sensed by the immune cells. Therefore, the lung microbiota develops, activates, and recruits immune cells to prevent inflammation in the lungs.

What Is the Role of Lung Microbiota in Lung Diseases?

Chronic lung disorders include chronic obstructive pulmonary disease (COPD), cystic fibrosis, and lung cancer. Microbiota dysbiosis accompanies or induces exacerbations of these disorders, characterized by acute worsening or decline in pulmonary function.

COPD

Exacerbations cause changes in the lung microbiota and airway inflammation. In severe conditions of COPD, an increase in the Firmicutes community is noted. This increases Lactobacillus species. Phagocytosis of Lactobacillus by macrophages reduces cigarette smoke-related inflammation. Hence, the lung microbiota helps to reduce inflammation in COPD.

Asthma

In asthmatic conditions, Proteobacteria is predominant in the airway. Short-chain fatty acid propionate generates macrophages and dendritic cells with high phagocytic and attenuating abilities to act against allergic inflammation.

Cystic Fibrosis

Cystic fibrosis is an autosomal disease of the lungs. This causes a shift in the lung microbiome. There is an increase in the bacterial burden resulting in airway inflammation. In addition, oral microbes predispose cystic fibrosis patients to subsequent infections.

Lung Cancer

Lung microbiota in cancer patients is Proteobacteria, Firmicutes, Actinobacteria, Bacteroides, and Verrucomicrobia. A significant shift in the microbiota may also cause lung cancer. Lung microbiota is an essential diagnostic and preventive marker in lung cancer. Veillonella and Megasphaera are potent lung cancer biomarkers. The lung microbiome is essential for the immune homeostasis of the mucous membrane in the lungs. Balance in the microbiome provokes an antitumor response. Probiotics may help in destroying cancer cells during chemotherapy.

What Is Its Relationship With GI Tract?

The gut harbors trillions of microbes. The gut and the lungs are connected through the chemical messengers produced by the microbiota. Alterations in gut microbiota are associated with lung disorders.

• Early-life asthma is associated with a decrease in Bifidobacteria and an increase in clostridia species.

• Depletion of gut microbiota due to antibiotics induces lung diseases and allergic inflammation.

• Neomycin causes gut dysbiosis and increases susceptibility to influenza virus infection.

Dysbiosis in the lung microbiota influences the gut microbiota.

• Influenza virus infection in the lungs increases Enterobacteriaceae and reduces Lactobacilli and Lactococci in the gut.

• Staphylococcus aureus or Pseudomonas aeruginosa infection in the lungs results in intestinal injury.

What Is the Role of Diet in Lung Function?

A fiber-rich diet is essential for gut microbiota and lung microbiota to modulate lung immunity. The gut microbiota assimilates dietary fiber to produce metabolites like short-chain fatty acids (SCFAs), which travel via the blood to protect against lung inflammation. A high-fiber diet reduces inflammatory markers and modulates innate immunity.

What Is the Role of Probiotics in Lung Diseases?

Probiotics are good microbes that have health benefits. They are present in yogurt, fermented foods, and dietary supplements.

• Probiotic bacteria like Lactobacillus rhamnosus, Bifidobacterium lactis, and Bifidobacterium breve modulates allergic response in asthma.

• Administration of Lactobacillus casei Shirota or Lactobacillus rhamnosus leads to a reduction in exacerbation symptoms in cystic fibrosis.

• Lactobacillus rhamnosus and Bifidobacterium breve suppress the inflammation induced by cigarette smoke-induced diseases like COPD.

• Probiotics enhance intestinal barrier function against antigens like lipopolysaccharides from reaching the lungs. And prevents inflammatory disorders like allergies, COPD, asthma, and inflammatory bowel disease.

• Administration of Lactobacillus acidophilus in lung cancer patients undergoing Cisplatin treatment shows a significant reduction in tumor size.

• Bifidobacterium cocktail (B.bifidum, B.longum, B.lactis, and B.breve) significantly reduces tumor size.

• Administering Enterococcus hirae and Barnesiella intestine hominis improves the efficacy of chemotherapy in lung cancer patients.

What Are the Future Perspectives on Lung Microbiome?

The lung microbiota plays a role in maintaining immune homeostasis and the pathogenesis of chronic lung disorders. Analyzing the effects of lung microbiota promotes the development of targeted therapies and the introduction of prognostic and diagnostic markers for chronic lung diseases.

The lung microbiome field is relatively new and requires human intervention and animal studies to address questions like:

• Is the microbiome the cause of the disease, a consequence of the disease, or both?

• Can microbiome-targeted sequence-based technologies act as markers to differentiate health and disease?

• Do environmental and other factors causing lung diseases influence the mechanism of injury of lung microbiota?

• What are the mechanisms by which the lung microbiota affects the host?

• Can microbiota be therapeutically manipulated by administering beneficial microbes by selective reduction of inflammatory mediators or by using microbially derived molecules with beneficial host effects?

Conclusion

The lung microbiome plays a significant role in health and disease. Impairment in the lung or gut microbiota increases the susceptibility to infections. It not only influences the susceptibility or cause of disease but is also affected by diseases. The gut-lung connection is vital in lung immunity. Dysbiosis in the gut and lung microbiota increases exacerbations of chronic lung diseases. Overall, a fiber-rich diet plays a major role in maintaining gut health, thereby preventing intestinal and lung disorders. This highlights the need for future studies on lung microbiota.