The dynamic lung microbiome in health and disease

Abstract

New methods and technologies within the field of lung biology are beginning to shed new light into the microbial world of the respiratory tract. Long considered to be a sterile environment, it is now clear that the human lungs are frequently exposed to live microbes and their by-products. The nature of the lung microbiome is quite distinct from other microbial communities inhabiting our bodies such as those in the gut. Notably, the microbiome of the lung exhibits a low biomass and is dominated by dynamic fluxes of microbial immigration and clearance, resulting in a bacterial burden and microbiome composition that is fluid in nature rather than fixed. As our understanding of the microbial ecology of the lung improves, it is becoming increasingly apparent that certain disease states can disrupt the microbial–host interface and ultimately affect disease pathogenesis. In this Review, we provide an overview of lower airway microbial dynamics in health and disease and discuss future work that is required to uncover novel therapeutic targets to improve lung health.

Neurological Disorder after Severe Pneumonia is Associated with Translocation of Bacteria from Lung to Brain

“…The lung is frequently exposed to air and contains a pulmonary microbial community, while its function is still controversial. Changes in the pulmonary microbial community seem to play a role in progression of pulmonary disorders 12 . In contrast, the brain should be a sterile environment under normal conditions, as the blood-brain barrier is able to prevent bacteria from entering the brain tissue.…”

“…Studies have shown that the brain and lung can communicate through a variety of ways, such as neuroanatomical pathway, endocrine pathway, and immune pathway etc. 11 The lung is an organ that contains microbiota 12 . The microbial community in the lung composes of about 140 distinct families, while most of their functions in healthy individuals are still unknown 12 .…”

Airway microbiome-immune crosstalk in chronic obstructive pulmonary disease

“…Airway microbiome sensing by bronchial epithelial cells, alveolar macrophages, and DCs activate innate lymphoid cells (ILCs) (7), which modulate other immune cells' activity. Depending on the type and degree of microbial exposure, DCs induce a wide range of immune responses, from immune tolerance induced by plasmacytoid DCs (pDCs) to inflammation induced by conventional DCs (cDCs) (8). Continuous microbial sampling and trafficking by activated DCs, and alveolar macrophages deliver processed microbial antigens to naïve CD4+T and CD8+T cells within mucosa-associated lymphoid tissue (MALT) and draining lymph nodes (8).…”

“…Foxp3+T cells drive IL-10 production, facilitating mucosal immune tolerance (7). In another mechanism, microbial-induced Tregs promote mucosal memory B or plasma cells' IgA secretion (8). Created with BioRender.com.…”

“…The mechanisms driving COPD progression have yet to become fully known. The airway microbiome has been implicated in several respiratory diseases, such as COPD, bronchiectasis, and asthma ( 8 ). However, it is still unclear how changes in airway microbiota drive persistent immune activation and consequent lung damage in COPD.…”