Delayed Microbial Maturation Durably Exacerbates Th17-driven Asthma in Mice

The gut microbiota modulates airway inflammation in allergic asthma through the gut-lung axis related immune modulation: A review

The human gut microbiota is a vast and complex microbial community. According to statistics, the number of bacteria residing in the human intestinal tract is approximately ten times that of total human cells, with over 1000 different species. The interaction between the gut microbiota and various organ tissues plays a crucial role in the pathogenesis of local and systemic diseases, exerting a significant influence on disease progression. The relationship between the gut microbiota and intestinal diseases, along with its connection to the pulmonary immune environment and the development of lung diseases, is commonly referred to as the "gut-lung axis." The incidence of bronchial asthma is rising globally. With ongoing research on gut microbiota, it is widely believed that intestinal microorganisms and their metabolic products directly or indirectly participate in the occurrence and development of asthma. Based on the gut-lung axis, this review examines recent research suggesting that the intestinal microbiota can influence the occurrence and progression of allergic asthma through the modulation of cytokine immune balance and mucosal integrity. Though the precise immune pathways or microbial species influencing asthma through the gut-lung axis are still under exploration, summarizing the immune modulation through the gut-lung axis in allergic asthma may provide insights for the clinical management of the condition.

Integrative Roles of Pro-Inflammatory Cytokines on Airway Smooth Muscle Structure and Function in Asthma

Asthma has become more appreciated for its heterogeneity with studies identifying type 2 and non-type 2 phenotypes/endotypes that ultimately lead to airflow obstruction, airway hyperresponsiveness, and remodeling. The pro-inflammatory environment in asthma influences airway smooth muscle (ASM) structure and function. ASM has a vast repertoire of inflammatory receptors that, upon activation, contribute to prominent features in asthma, notably immune cell recruitment and activation, hypercontractility, proliferation, migration, and extracellular matrix protein deposition. These pro-inflammatory responses in ASM can be mediated by both type 2 (e.g., IL-4, IL-13, and TSLP) and non-type 2 (e.g., TNFα, IFNγ, IL-17A, and TGFβ) cytokines, highlighting roles for ASM in type 2 and non-type 2 asthma phenotypes/endotypes. In recent years, there has been considerable advances in understanding how pro-inflammatory cytokines promote ASM dysfunction and impair responsiveness to asthma therapy, corticosteroids and long-acting β2-adrenergic receptor agonists (LABAs). Transcriptomic analyses on human ASM cells and tissues have expanded our knowledge in this area but have also raised new questions regarding ASM and its role in asthma. In this review, we discuss how pro-inflammatory cytokines, corticosteroids, and LABAs affect ASM structure and function, with particular focus on changes in gene expression and transcriptional programs in type 2 and non-type 2 asthma.

Maternal OM-85 administration alleviates offspring allergic airway inflammation by downregulating IL-33/ILC2 axis

BACKGROUND

Type 2 innate lymphoid cells (ILC2s) are essential for maintaining immune regulation and promoting tissue homeostasis in allergic asthma. How the development of gut microbiota on neonatal ILC2s influences allergic airway inflammation remains unclear. Here we focus on offspring ILC2 development in the context of alterations in maternal gut microbiota.

METHODS

C57BL/6 maternal mice were gavaged with OM-85 during pregnancy and/or lactation, ILC2-driven allergic airway inflammation in the OVA-sensitized adult offspring was observed. ILC2 development in offspring early life were investigated using recombinant (r)IL-33, rIL-25 and Bromodeoxyuridine in the vivo experiments. Further ILC2 promoting factors- IL-33 and IL-25 production in offspring early life were analysed. Finally, we examined the changes in gut microbiota and its metabolites in both dams and pups, and explored the effects of short-chain fatty acids (SCFAs) on IL-33 expression and secretion.

RESULTS

Maternal OM-85 administration restrained ILC2-driven allergic airway inflammation in the OVA-sensitized adult offspring. During ILC2 development in offspring early life, maternal OM-85 administration suppressed IL-33 and IL-25 production to inhibit ILC2 expansion and ILC2 responsiveness to alarmins, and infantile ILC2s could persist into adulthood. Maternal OM-85 administration increased SCFAs in breast milk and SCFA-producing gut probiotics (predominant Bacteroides and Blautia) in offspring, especially during pregnancy and lactation. SCFAs down-regulated IL-33 expression and reduced IL-33 secretion by inhibited gasdermin D (GSDMD) formation.

CONCLUSION

Maternal OM-85 administration restrains ILC2-driven allergic airway inflammation in adult offspring by increasing offspring intestinal SCFAs to modulate ILC2 development at an early stage, demonstrating that the transgenerational effects of maternal OM-85 exposure on offspring innate immunity.

Lung microbiota: implications and interactions in chronic pulmonary diseases

The lungs, as vital organs in the human body, continuously engage in gas exchange with the external environment. The lung microbiota, a critical component in maintaining internal homeostasis, significantly influences the onset and progression of diseases. Beneficial interactions between the host and its microbial community are essential for preserving the host's health, whereas disease development is often linked to dysbiosis or alterations in the microbial community. Evidence has demonstrated that changes in lung microbiota contribute to the development of major chronic lung diseases, including chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), asthma, and lung cancer. However, in-depth mechanistic studies are constrained by the small scale of the lung microbiota and its susceptibility to environmental pollutants and other factors, leaving many questions unanswered. This review examines recent research on the lung microbiota and lung diseases, as well as methodological advancements in studying lung microbiota, summarizing the ways in which lung microbiota impacts lung diseases and introducing research methods for investigating lung microbiota.

The respiratory microbiome in childhood asthma

Asthma is the most prevalent noncommunicable disease in childhood, characterized by reversible airway constriction and inflammation of the lower airways. The respiratory tract consists of the upper and lower airways, which are lined with a diverse community of microbes. The composition and density of the respiratory microbiome differs across the respiratory tract, with microbes adapting to the gradually changing physiology of the environment. Over the past decade, both the upper and lower respiratory microbiomes have been implicated in the etiology and disease course of asthma, as well as in its severity and phenotype. We have reviewed the literature on the role of the respiratory microbiome in asthma, making a careful distinction between the relationship of the microbiome with development of childhood asthma and its relationship with the disease course, while accounting for age and the microbial niches studied. Furthermore, we have assessed the literature regarding the underlying asthma endotypes and the impact of the microbiome on the host immune response. We have identified distinct microbial signatures across the respiratory tract associated with asthma development, stability, and severity. These data suggest that the respiratory microbiome may be important for asthma development and severity and may therefore be a potential target for future microbiome-based preventive and treatment strategies.