Microbiome-Immune Interactions in Allergy and Asthma

RSV infection in neonatal mice and gastrointestinal microbiome alteration contribute to allergic predisposition

Severe respiratory syncytial virus (RSV) infection during infancy is associated with a 2 to 4-fold increased risk for the development of wheezing and asthma. Recent studies have implicated microbiome changes, either within the lung or gut, during early life can also affect the development of pulmonary disease. Our studies demonstrate long-term gastrointestinal and lung microbiome changes following early life (EL) RSV infection. To determine the respective roles of ELRSV infection and the gut microbiome, we performed germ-free neonatal infection and microbiome colonization using a microbiome from an uninfected animal followed by cockroach allergen (CRA)-induced asthma 4 weeks later. Germ-free animals with ELRSV infection displayed increased airway disease that was diminished by microbiome colonization, including airway hyperreactivity (AHR), mucus, and eosinophil infiltration. To address the role of virus induced gastrointestinal microbiome alterations, we utilized GF mice conventionalized with RSV-associated or naive microbiomes followed by CRA-induced disease. Transfer of neonatal microbiome taken during acute RSV infection did not alter the allergic response to CRA. However, the transfer of a naive adult microbiome conferred protection from enhanced AHR in response to CRA whereas an RSV associated microbiome did not. Taken together, our data indicate that microbiome alteration and early life RSV infection both contribute to allergic predisposition.

Perturbations in the airway microbiome are associated with type 2 asthma phenotype and severity

BACKGROUND

Airway microbiome has been linked to asthma heterogeneity, yet little is known about the associations between airway microbiota and type 2 (T2) asthma phenotype and severity.

OBJECTIVE

To determine the relationship of nasopharyngeal (NP) and induced sputum (IS) microbiota to the phenotypic features of T2 asthma.

METHODS

NP and IS samples from subjects with T2 mild-to-moderate asthma (n = 23), subjects with severe asthma (n = 21), and healthy controls (n = 16) were analyzed. Bacterial microbiota and functional profiles were compared. The correlation between microbial communities and clinical and inflammatory features was evaluated in individuals with asthma of 2 statuses.

RESULTS

Differences in NP and IS microbiota were associated with T2 asthma phenotype. Alterations in NP microbiota were more reflective of T2 inflammation and severity, with additional stratification of a subgroup characterized by significant elevations in T2 inflammatory biomarkers and reductions in bacterial richness and diversity (P < .05). Burkholderia-Caballeronia-Paraburkholderia, Ralstonia, and Rhodococcus were identified as hub taxa within NP microbial network in T2 severe asthma, which were prevalent in the entire airway and involved in bacterial functions including inflammatory and steroid responses (P < .05). The composition and diversity of IS microbiota were complex, with Veillonella as the most altered genus, having an increase with increasing asthma severity.

CONCLUSION

Our work revealed the significant associations of microbiota perturbations throughout the entire respiratory tract to the extent of T2 inflammation, phenotype and severity in T2 asthma. The specific taxa identified invite further mechanistic investigations to unravel their possibility as biomarkers and therapeutic targets for T2 severe asthma.

Microbiome modifications by steroids during viral exacerbation of asthma and in healthy mice

In the present studies, the assessment of how viral exacerbation of asthmatic responses with and without pulmonary steroid treatment alters the microbiome in conjunction with immune responses presents striking data. The overall findings identify that although steroid treatment of allergic animals diminished the severity of the respiratory syncytial virus (RSV)-induced exacerbation of airway function and mucus hypersecretion, there were local increases in IL-17 expression. Analysis of the lung and gut microbiome suggested that there are differences in RSV exacerbation that are further altered by fluticasone (FLUT) treatment. Using metagenomic inference software, PICRUSt2, we were able to predict that the metabolite profile produced by the changed gut microbiome was significantly different with multiple metabolic pathways and associated with specific treatments with or without FLUT. Importantly, measuring plasma metabolites in an unbiased manner, our data indicate that there are significant changes associated with chronic allergen exposure, RSV exacerbation, and FLUT treatment that are reflective of responses to the disease and treatment. In addition, the changes in metabolites appeared to have contributions from both host and microbial pathways. To understand if airway steroids on their own altered lung and gut microbiome along with host responses to RSV infection, naïve animals were treated with lung FLUT before RSV infection. The naïve animals treated with FLUT before RSV infection demonstrated enhanced disease that corresponded to an altered microbiome and the related PICRUSt2 metagenomic inference analysis. Altogether, these findings set the foundation for identifying important correlations of severe viral exacerbated allergic disease with microbiome changes and the relationship of host metabolome with a potential for early life pulmonary steroid influence on subsequent viral-induced disease.NEW & NOTEWORTHY These studies outline a novel finding that airway treatment with fluticasone, a commonly used inhaled steroid, has significant effects on not only the local lung environment but also on the mucosal microbiome, which may have significant disease implications. The findings further provide data to support that pulmonary viral exacerbations of asthma with or without steroid treatment alter the lung and gut microbiome, which have an impact on the circulating metabolome that likely alters the trajectory of disease progression.

Asthma Pathogenesis: Phenotypes, Therapies, and Gaps: Summary of the Aspen Lung Conference 2023

Although substantial progress has been made in our understanding of asthma pathogenesis and phenotypes over the nearly 60-year history of the Aspen Lung Conferences on asthma, many ongoing challenges exist in our understanding of the clinical and molecular heterogeneity of the disease and an individual patient's response to therapy. This report summarizes the proceedings of the 2023 Aspen Lung Conference, which was organized to review the clinical and molecular heterogeneity of asthma and to better understand the impact of genetic, environmental, cellular, and molecular influences on disease susceptibility, heterogeneity, and severity. The goals of the conference were to review new information about asthma phenotypes, cellular processes, and cellular signatures underlying disease heterogeneity and treatment response. The report concludes with ongoing gaps in our understanding of asthma pathobiology and provides some recommendations for future research to better understand the clinical and basic mechanisms underlying disease heterogeneity in asthma and to advance the development of new treatments for this growing public health problem.

Cross-domain microbiomes: the interaction of gut, lung and environmental microbiota in asthma pathogenesis

Recent experimental and epidemiological studies underscore the vital interaction between the intestinal microbiota and the lungs, an interplay known as the "gut-lung axis". The significance of this axis has been further illuminated following the identification of intestinal microbial metabolites, such as short-chain fatty acids (SCFA), as key mediators in setting the tone of the immune system. Through the gut-lung axis, the gut microbiota and its metabolites, or allergens, are directly or indirectly involved in the immunomodulation of pulmonary diseases, thereby increasing susceptibility to allergic airway diseases such as asthma. Asthma is a complex outcome of the interplay between environmental factors and genetic predispositions. The concept of the gut-lung axis may offer new targets for the prevention and treatment of asthma. This review outlines the relationships between asthma and the respiratory microbiome, gut microbiome, and environmental microbiome. It also discusses the current advancements and applications of microbiomics, offering novel perspectives and strategies for the clinical management of chronic respiratory diseases like asthma.

Pre-asthma: a useful concept for prevention and disease-modification? A EUFOREA paper. Part 1-allergic asthma

Asthma, which affects some 300 million people worldwide and caused 455,000 deaths in 2019, is a significant burden to suffers and to society. It is the most common chronic disease in children and represents one of the major causes for years lived with disability. Significant efforts are made by organizations such as WHO in improving the diagnosis, treatment and monitoring of asthma. However asthma prevention has been less studied. Currently there is a concept of pre- diabetes which allows a reduction in full blown diabetes if diet and exercise are undertaken. Similar predictive states are found in Alzheimer's and Parkinson's diseases. In this paper we explore the possibilities for asthma prevention, both at population level and also investigate the possibility of defining a state of pre-asthma, in which intensive treatment could reduce progression to asthma. Since asthma is a heterogeneous condition, this paper is concerned with allergic asthma. A subsequent one will deal with late onset eosinophilic asthma.

Global knowledge mapping and emerging research trends in the microbiome and asthma: A bibliometric and visualized analysis using VOSviewer and CiteSpace

Background

Numerous prior studies have extensively highlighted the significance of the microbiome in association with asthma. While several studies have concentrated on the asthma microbiome in previous research, there is currently a lack of publications that employ bibliometric methods to assess this area.

Methods

In this study, the Web of Science Core Collection database was utilized as the data source, and the SCI-EXPANDED index was employed to ensure that the retrieved data were comprehensive and accurate. All original research articles and review articles related to the correlation between asthma and the microbiome were systematically searched from the inception of the database until June 20, 2023. These articles were subsequently visualized and analyzed using VOSviewer and CiteSpace software.

Results

A total of 1366 relevant publications were acquired, indicating a consistent annual increase in global publications in the field. The United States and China emerged as the top two contributors to international publications. Among prolific authors, Susan V. Lynch achieved the highest publication record, with Hans Bisgaard and Jakob Stokholm sharing the second position. The majority of publications concentrated on allergy-related and microbiome areas, with a few comprehensive journals standing out. Journals with 40 or more publications included the Journal of Allergy and Clinical Immunology, Allergy, Frontiers in Immunology, and PLOS One. The top 5 cited journals were the Journal of Allergy and Clinical Immunology, PLOS One, American Journal of Respiratory and Critical Care Medicine, Clinical and Experimental Allergy, and Nature. Upon analyzing keywords, high-frequency terms, such as asthma, gut microbiota, microbiome, children, childhood asthma, allergy, risk, exposure, inflammation, diversity, and chain fatty acids emerged as representative terms in the field.

Conclusion

This study systematically presented a comprehensive overview of the literature regarding the association between asthma and the microbiome over the last two decades. Through a bibliometric perspective, the findings may assist researchers with a better understanding of the essential information in the field.

The re-emerging role of linoleic acid in paediatric asthma

Asthma is the most common chronic disease within the paediatric population. Although it is multifactorial, its onset may be linked to early-life exposures with subsequent impact on immune system development. Microbial and dietary metabolic products have been implicated in the development and exacerbation of paediatric asthma. Linoleic acid is the most common omega-6 polyunsaturated fatty acid in the Western diet. In this review, we summarise the literature regarding the involvement of linoleic acid in the development of and its impact on existing paediatric asthma. First, we summarise the existing knowledge surrounding the relationship between human microbial metabolism and allergic diseases in children. Next, we examine cellular or animal model-based mechanistic studies that investigated the impact of dietary- and microbial-derived linoleic acid metabolites on asthma. Finally, we review the literature investigating the impact of linoleic acid metabolites on the development and exacerbation of childhood asthma. While there is conflicting evidence, there is growing support for a role of linoleic acid in the onset and pathophysiology of asthma. We recommend that additional cellular, animal, and longitudinal studies are performed that target linoleic acid and its metabolites.

Severe Asthma and Biological Therapies: Now and the Future

Recognition of phenotypic variability in pediatric asthma allows for a more personalized therapeutic approach. Knowledge of the underlying pathophysiological and molecular mechanisms (endotypes) of corresponding biomarkers and new treatments enables this strategy to progress. Biologic therapies for children with severe asthma are becoming more relevant in this sense. The T2 phenotype is the most prevalent in childhood and adolescence, and non-T2 phenotypes are usually rare. This document aims to review the mechanism of action, efficacy, and potential predictive and monitoring biomarkers of biological drugs, focusing on the pediatric population. The drugs currently available are omalizumab, mepolizumab, benralizumab, dupilumab, and 1ezepelumab, with some differences in administrative approval prescription criteria between the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA). Previously, we described the characteristics of severe asthma in children and its diagnostic and therapeutic management.

Impact of local human microbiota on the allergic diseases: Organ-organ interaction

The homogeneous impact of local dysbiosis on the development of allergic diseases in the same organ has been thoroughly studied. However, much less is known about the heterogeneous influence of dysbiosis within one organ on allergic diseases in other organs. A comprehensive analysis of the current scientific literature revealed that most of the relevant publications focus on only three organs: gut, airways, and skin. Moreover, the interactions appear to be mainly unidirectional, that is, dysbiotic conditions of the gut being associated with allergic diseases of the airways and the skin. Similar to homogeneous interactions, early life appears to be not only a crucial period for the formation of the microbiota in one organ but also for the later development of allergic diseases in other organs. In particular, we were able to identify a number of specific bacterial and fungal species/genera in the intestine that were repeatedly associated in the literature with either increased or decreased allergic diseases of the skin, like atopic dermatitis, or the airways, like allergic rhinitis and asthma. The reported studies indicate that in addition to the composition of the microbiome, also the relative abundance of certain microbial species and the overall diversity are associated with allergic diseases of the corresponding organs. As anticipated for human association studies, the underlying mechanisms of the organ-organ crosstalk could not be clearly resolved yet. Thus, further work, in particular experimental animal studies are required to elucidate the mechanisms linking dysbiotic conditions of one organ to allergic diseases in other organs.

Effects of Lactobacillus on the Differentiation of Intestinal Mucosa Immune Cells and the Composition of Gut Microbiota in Soybean-Sensitized Mice

In the early stage of this study, three strains of Lactobacillus with anti-soybean allergy potential were screened: Lactobacillus acidophilus CICC 6081, Lactobacillus delbrueckii subsp. Bulgaricus CICC 6103 and Lactobacillus plantarum subsp. Plantarum CICC 20988. The aim of this study was to analyze the desensitization effect of three strains of Lactobacillus administered by gavage to soybean-allergic mice through the differentiation of immune cells in intestinal lymph nodes and the changes to gut microbiota. The results showed that the three strains of Lactobacillus could stimulate the proliferation of dendritic cells (DCs) and regulate the balance of Th1/Th2 differentiation in the MLNs and PPs of soybean-allergic mice. Furthermore, the Th17/Tregs cell-differentiation ratio in the MLNs of the Lactobacillus-treated mice was significantly lower than that of the allergic mice (p < 0.05). Compared to the control group, the Shannon, Sobs and Ace indexes of intestinal microbiota in the allergic mice were significantly increased (p < 0.05), and the proportion of Clostridiales was significantly higher (p < 0.05), which was reversed by Lactobacillus gavage. In conclusion, the three strains of Lactobacillus can inhibit the intestinal mucosal immune response and regulate gut microbiota balance in soybean-allergic mice.

Microbiome and Asthma: Microbial Dysbiosis and the Origins, Phenotypes, Persistence, and Severity of Asthma

The importance of the microbiome, and of the gut-lung axis in the origin and persistence of asthma, is an ongoing field of investigation. The process of microbial colonisation in the first three years of life is fundamental for health, with the first hundred days of life being critical. Different factors are associated with early microbial dysbiosis, such as caesarean delivery, artificial lactation and antibiotic therapy, among others. Longitudinal cohort studies on gut and airway microbiome in children have found an association between microbial dysbiosis and asthma at later ages of life. A low α-diversity and relative abundance of certain commensal gut bacterial genera in the first year of life are associated with the development of asthma. Gut microbial dysbiosis, with a lower abundance of Phylum Firmicutes, could be related with increased risk of asthma. Upper airway microbial dysbiosis, especially early colonisation by Moraxella spp., is associated with recurrent viral infections and the development of asthma. Moreover, the bacteria in the respiratory system produce metabolites that may modify the inception of asthma and is progression. The role of the lung microbiome in asthma development has yet to be fully elucidated. Nevertheless, the most consistent finding in studies on lung microbiome is the increased bacterial load and the predominance of proteobacteria, especially Haemophilus spp. and Moraxella catarrhalis. In this review we shall update the knowledge on the association between microbial dysbiosis and the origins of asthma, as well as its persistence, phenotypes, and severity.