Different Airway Inflammatory Phenotypes Correlate with Specific Fungal and Bacterial Microbiota in Asthma and Chronic Obstructive Pulmonary Disease

Narrative review: respiratory tract microbiome and never smoking lung cancer

Background and Objective

The lung microbiome was previously thought to be a sterile environment where only gaseous exchange takes place, but recent studies have shown the presence of microbiota in the lung. This review investigates the current literature on the effects of an environmental driven dysbiosis on the healthy oral and respiratory microbiome and its relationship to lung cancer risk in never-smokers.

Methods

An online electronic search was performed on PubMed of all English-language literature using combinations of the following keywords: "lung cancer", "dysbiosis", "non-smokers", "oral microbiome", and "respiratory microbiome". All population-based studies reporting results on oral and/or respiratory microbiome in adults were considered for our narrative review.

Key Content and Findings

Metagenomic analyses have been performed on isolated samples from healthy participants and compared to samples from those with lung cancer. Research shows that a decrease in alpha diversity of microbes in the oral microbiome is associated with increased risk of lung cancer, along with differences in beta diversity in the sputum of lung cancer cases and healthy controls. Further, several studies have observed that significant changes in the abundance of genera such as increased abundance of Lactobacillales, Bacilli, and Firmicutes associated with an increased lung cancer risk among participants with exposure to certain household solid fuels.

Conclusions

These findings suggest potential carcinogenic processes such as increased inflammation associated with changes in flora. Additionally, studies showed that increase in certain taxa such as Bacteroides and Spirochetes might have a protective effect on lung cancer risk. The review also provides insight into how understanding the microbial changes can be beneficial for lung cancer treatment and disease-free survival. Larger studies in different populations need to be performed to strengthen the current associations between microbial diversity and lung cancer risk.

Human matters in asthma: Considering the microbiome in pulmonary health

Microbial communities form an important symbiotic ecosystem within humans and have direct effects on health and well-being. Numerous exogenous factors including airborne triggers, diet, and drugs impact these established, but fragile communities across the human lifespan. Crosstalk between the mucosal microbiota and the immune system as well as the gut-lung axis have direct correlations to immune bias that may promote chronic diseases like asthma. Asthma initiation and pathogenesis are multifaceted and complex with input from genetic, epigenetic, and environmental components. In this review, we summarize and discuss the role of the airway microbiome in asthma, and how the environment, diet and therapeutics impact this low biomass community of microorganisms. We also focus this review on the pediatric and Black populations as high-risk groups requiring special attention, emphasizing that the whole patient must be considered during treatment. Although new culture-independent techniques have been developed and are more accessible to researchers, the exact contribution the airway microbiome makes in asthma pathogenesis is not well understood. Understanding how the airway microbiome, as a living entity in the respiratory tract, participates in lung immunity during the development and progression of asthma may lead to critical new treatments for asthma, including population-targeted interventions, or even more effective administration of currently available therapeutics.

Impact of Lung Microbiota on COPD

There is a fine balance in maintaining healthy microbiota composition, and its alterations due to genetic, lifestyle, and environmental factors can lead to the onset of respiratory dysfunctions such as chronic obstructive pulmonary disease (COPD). The relationship between lung microbiota and COPD is currently under study. Little is known about the role of the microbiota in patients with stable or exacerbated COPD. Inflammation in COPD disorders appears to be characterised by dysbiosis, reduced lung activity, and an imbalance between the innate and adaptive immune systems. Lung microbiota intervention could ameliorate these disorders. The microbiota’s anti-inflammatory action could be decisive in the onset of pathologies. In this review, we highlight the feedback loop between microbiota dysfunction, immune response, inflammation, and lung damage in relation to COPD status in order to encourage the development of innovative therapeutic goals for the prevention and management of this disease.

Clinical Aspergillus Signatures in COPD and Bronchiectasis

Pulmonary mycoses remain a global threat, causing significant morbidity and mortality. Patients with airways disease, including COPD and bronchiectasis, are at increased risks of pulmonary mycoses and its associated complications. Frequent use of antibiotics and corticosteroids coupled with impaired host defenses predispose patients to fungal colonization and airway persistence, which are associated with negative clinical consequences. Notably, Aspergillus species remain the best-studied fungal pathogen and induce a broad spectrum of clinical manifestations in COPD and bronchiectasis ranging from colonization and sensitization to more invasive disease. Next-generation sequencing (NGS) has gained prominence in the field of respiratory infection, and in some cases is beginning to act as a viable alternative to traditional culture. NGS has revolutionized our understanding of airway microbiota and in particular fungi. In this context, it permits the identification of the previously unculturable, fungal composition, and dynamic change within microbial communities of the airway, including potential roles in chronic respiratory disease. Furthermore, inter-kingdom microbial interactions, including fungi, in conjunction with host immunity have recently been shown to have important clinical roles in COPD and bronchiectasis. In this review, we provide an overview of clinical Aspergillus signatures in COPD and bronchiectasis and cover the current advances in the understanding of the mycobiome in these disease states. The challenges and limitations of NGS will be addressed.