Lung Microbiota and Its Impact on the Mucosal Immune Phenotype

Abstract

The use of culture-independent techniques has allowed us to appreciate that the upper and lower respiratory tract contain a diverse community of microbes in health and disease. Research has only recently explored the effects of the microbiome on the host immune response. The exposure of the human body to the bacterial environment is an important factor for immunological development; thus, the interaction between the microbiome and its host is critical to understanding the pathogenesis of disease. In this article, we discuss the mechanisms that determine the composition of the airway microbiome and its effects on the host immune response. With the use of ecological principles, we have learned how the lower airways constitute a unique niche subjected to frequent microbial migration (e.g., through aspiration) and constant immunological pressure. The discussion will focus on the possible inflammatory pathways that are up- and downregulated when the immune system is challenged by dysbiosis. Identification of potential markers and microbial targets to address the modulation of inflammation in early disease, when changes may have the most effect, will be critical for future therapies.

Respiratory Bordetella bronchiseptica Carriage is Associated with Broad Phenotypic Alterations of Peripheral CD4+CD25+ T Cells and Differentially Affects Immune Responses to Secondary Non-Infectious and Infectious Stimuli in Mice

“…Currently, increasing attention is being directed to the interactions between responses to different simultaneous or sequential immunologically relevant stimuli in single hosts. Furthermore, next to the gut and skin, the lower respiratory tract is now being acknowledged as a niche for colonization by harmless and potentially harmful microorganisms [ 1 , 2 ]. The questions arising are, what regulatory mechanisms are potentially induced through respiratory pathogen carriage and how these affect the response to secondary immunological triggers.…”

“…The lung as the central site of gas exchange is, together with the conducting airways, constantly exposed to all kinds of environmental factors and thereby confronted with potential hazards, such as pollutants and pathogenic microorganisms. While it was long believed to represent a sterile compartment, research of the last years has delivered evidence that the lower respiratory tract displays a favorable niche for commensal microorganisms [ 1 , 2 ]. The lungs central role in oxygen supply, its delicate structure, its constant exposure to harmful as well as harmless microorganisms, and its potential to serve as an entry site for invading pathogens, altogether demand for an effective and at the same time tightly regulated immune system.…”

Epithelial MHC Class II Expression and Its Role in Antigen Presentation in the Gastrointestinal and Respiratory Tracts

“…Though the lung and gut share a common origin at the oropharynx, microbial populations are vastly different. The lung is not completely sterile but has a much lower bacterial burden without a characteristic microbiome like the gut; rather, lung flora tends to resemble oral flora and may change in response to a variety of stimuli and pathologies ( 161 , 162 ).…”

Perspectives on Probiotics and Bronchopulmonary Dysplasia

“…The incipient composition of the lung microbiota cannot be neglected because it is closely related to the onset of mucosal immunity (18), the development of immune tolerance in the lungs (19), and healthy breathing (15). Several reports have shown alterations in the stability and diversity of the respiratory tract microbiota in BPD.…”