Pathogenesis of Children's Allergic Diseases: Refocusing the Role of the Gut Microbiota

Gut microbiota of one-and-a-half-year-old food-allergic and healthy children

BACKGROUND

Intestinal bacteria may play a role in the development of food allergies. This study aimed to analyze and compare the gut microbiota of food-allergic children with that of healthy children of the same age.

METHODS

Stool samples were collected from one-and-a-half-year-old food-allergic (FA group, n = 29) and healthy controls (HC group, n = 19). A questionnaire was provided to examine the children's birth, dietary, medical, and social histories. The gut microbiota was profiled by 16S rRNA sequencing. Differences in taxonomic composition were assessed using linear discriminant analysis effect size (LEfSe), and microbial functional profiles were predicted with Tax4Fun2.

RESULTS

No significant difference in the alpha diversity index between the two groups; however, a negative correlation was observed between the Shannon diversity index and the relative abundance of Bacteroides. A significant difference was observed in beta diversity (permutational multivariate analysis of variance) in the bacterial composition between the FA and HC groups (P < 0.05). The FA group had a higher abundance of Escherichia and Anaeromassilibacillus and a lower abundance of Bacteroides, Oscillibacter, Ruminococcus, Hungateiclostridium and Anaerotaenia than the HC group (LEfSe: linear discriminant analysis score >2). The FA group showed a predicted increase in the expression levels of genes associated with intestinal pathogenicity compared with that in the HC group.

CONCLUSIONS

The gut microbiota of food-allergic children has a higher abundance of bacteria involved in intestinal inflammation and a lower abundance of bacteria involved in immune tolerance than that of healthy children. This dysbiosis may also be associated with food allergies.

The Microbiota and Equine Asthma: An Integrative View of the Gut-Lung Axis

Both microbe-microbe and host-microbe interactions can have effects beyond the local environment and influence immunological responses in remote organs such as the lungs. The crosstalk between the gut and the lungs, which is supported by complex connections and intricate pathways, is defined as the gut-lung axis. This review aimed to report on the potential role of the gut-lung gut-lung axis in the development and persistence of equine asthma. We summarized significant determinants in the development of asthma in horses and humans. The article discusses the gut-lung axis and proposes an integrative view of the relationship between gut microbiota and asthma. It also explores therapies for modulating the gut microbiota in horses with asthma. Improving our understanding of the horse gut-lung axis could lead to the development of techniques such as fecal microbiota transplants, probiotics, or prebiotics to manipulate the gut microbiota specifically for improving the management of asthma in horses.

Reversible aberrancies in gut microbiome of moderate and late preterm infants: results from a randomized, controlled trial

The aim of this study was to obtain insight into the composition and function of the deviant gut microbiome throughout infancy in children born moderately and late preterm and their response to microbiome modulation. We characterized the longitudinal development of the gut microbiome from birth to the age of 12 months by metagenomic sequencing in 43 moderate and late preterm children participating in a randomized, controlled trial (ClinicalTrials.gov/no.NCT00167700) assessing the impact of a probiotic (Lactobacillus rhamnosus GG, ATCC 53,103, currently Lacticaseibacillus rhamnosus GG) and a prebiotic (galacto-oligosaccharide and polydextrose mixture, 1:1) intervention as compared to a placebo administered from 3 to 60 days of life. In addition, 9 full-term, vaginally delivered, breast-fed infants, who remained healthy long-term were included as references. Significant differences in taxonomy, but not in functional potential, were found when comparing the gut microbiome composition of preterm and full-term infants during the first month of life. However, the gut microbiome of preterm infants resembled that of full-term infants by 6 months age. Probiotic and prebiotic treatments were found to mitigate the shift in the microbiome of preterm infants by accelerating Bifidobacteria-dominated gut microbiome in beta diversity analysis. This study provides intriguing information regarding the establishment of the gut microbiome in children born moderately and late preterm, representing the majority of children born preterm. Specific pro- and prebiotics may reverse the proinflammatory gut microbiome composition during the vulnerable period, when the microbiome is low in resilience and susceptible to environmental exposure and simultaneously promotes immunological and metabolic maturation.

Lung Microbiome as a Treatable Trait in Chronic Respiratory Disorders

Once thought to be a sterile environment, it is now established that lungs are populated by various microorganisms that participate in maintaining lung function and play an important role in shaping lung immune surveillance. Although our comprehension of the molecular and metabolic interactions between microbes and lung cells is still in its infancy, any event causing a persistent qualitative or quantitative variation in the composition of lung microbiome, termed "dysbiosis", has been virtually associated with many respiratory diseases. A deep understanding of the composition and function of the "healthy" lung microbiota and how dysbiosis can cause or participate in disease progression will be pivotal in finding specific therapies aimed at preventing diseases and restoring lung function. Here, we review lung microbiome dysbiosis in different lung pathologies and the mechanisms by which these bacteria can cause or contribute to the severity of the disease. Furthermore, we describe how different respiratory disorders can be caused by the same pathogen, and that the real pathogenetic mechanism is not only dependent by the presence and amount of the main pathogen but can be shaped by the interaction it can build with other bacteria, fungi, and viruses present in the lung. Understanding the nature of this bacteria crosstalk could further our understanding of each respiratory disease leading to the development of new therapeutic strategies.

The First 1000 Days of Life: How Changes in the Microbiota Can Influence Food Allergy Onset in Children

BACKGROUND

Allergic disease, including food allergies (FA)s, has been identified as a major global disease. The first 1000 days of life can be a "window of opportunity" or a "window of susceptibility", during which several factors can predispose children to FA development. Changes in the composition of the gut microbiota from pregnancy to infancy may play a pivotal role in this regard: some bacterial genera, such as Lactobacillus and Bifidobacterium, seem to be protective against FA development. On the contrary, Clostridium and Staphylococcus appear to be unprotective.

METHODS

We conducted research on the most recent literature (2013-2023) using the PubMed and Scopus databases. We included original papers, clinical trials, meta-analyses, and reviews in English. Case reports, series, and letters were excluded.

RESULTS

During pregnancy, the maternal diet can play a fundamental role in influencing the gut microbiota composition of newborns. After birth, human milk can promote the development of protective microbial species via human milk oligosaccharides (HMOs), which play a prebiotic role. Moreover, complementary feeding can modify the gut microbiota's composition.

CONCLUSIONS

The first two years of life are a critical period, during which several factors can increase the risk of FA development in genetically predisposed children.

Early Prediction of Asthma

The clinical manifestations of asthma in children are highly variable, are associated with different molecular and cellular mechanisms, and are characterized by common symptoms that may diversify in frequency and intensity throughout life. It is a disease that generally begins in the first five years of life, and it is essential to promptly identify patients at high risk of developing asthma by using different prediction models. The aim of this review regarding the early prediction of asthma is to summarize predictive factors for the course of asthma, including lung function, allergic comorbidity, and relevant data from the patient's medical history, among other factors. This review also highlights the epigenetic factors that are involved, such as DNA methylation and asthma risk, microRNA expression, and histone modification. The different tools that have been developed in recent years for use in asthma prediction, including machine learning approaches, are presented and compared. In this review, emphasis is placed on molecular mechanisms and biomarkers that can be used as predictors of asthma in children.

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.

Phenotype-specific signatures of systems-level gut microbiome associated with childhood airway allergies

BACKGROUND

Perturbation of gut symbiosis has been linked to childhood allergic diseases. However, the underlying host-microbe interaction connected with specific phenotypes is poorly understood.

METHODS

To address this, integrative analyses of stool metagenomic and metabolomic profiles associated with IgE reactions in 56 children with mite-sensitized airway allergies (25 with rhinitis and 31 with asthma) and 28 nonallergic healthy controls were conducted.

RESULTS

We noted a decrease in the number and abundance of gut microbiome-encoded carbohydrate-active enzyme (CAZyme) genes, accompanied with a reduction in species richness, in the asthmatic gut microflora but not in that from allergic rhinitis. Such loss of CAZymes was consistent with the observation that a CAZyme-linked decrease in fecal butyrate was found in asthmatics and negatively correlated with mite-specific IgE responses. Different from the CAZymes, we demonstrated an increase in α diversity at the virulome levels in asthmatic gut microbiota and identified phenotype-specific variations of gut virulome. Moreover, use of fecal metagenomic and metabolomic signatures resulted in distinct effects on differentiating rhinitis and asthma from nonallergic healthy controls.

CONCLUSION

Overall, our integrative analyses reveal several signatures of systems-level gut microbiome in robust associations with fecal metabolites and disease phenotypes, which may be of etiological and diagnostic implications in childhood airway allergies.

Biotics in atopic diseases: state of the art and future perspectives

Prevalence of allergic diseases has growing in recent decades, being a significant burden for patients and their families. Different environmental factors, acting in early life, can significantly affect the timing and diversity of bacterial colonization and the immune system development. Growing evidence points to a correlation between early life microbial perturbation and development of allergic diseases. Besides, changes in the microbiota in one body site may influence other microbiota communities at distance by different mechanisms, including microbial-derived metabolites, mainly the short chain fatty acids (SCFA). Hence, there has been an increasing interest on the role of "biotics" (probiotics, prebiotics, symbiotics and postbiotics) in shaping dysbiosis and modulating allergic risk. Systemic type 2 inflammation is emerging as a common pathogenetic pathway of allergic diseases, intertwining communication with the gut mcirobiota. The aim of this review was to provide an update overview of the current knowledge of biotics in prevention and treatment of allergic diseases, also addressing research gaps which need to be filled.

Association of vitamin A supplementation with immune-related allergic diseases: A meta-analysis

BACKGROUND

Allergic diseases are type I hypersensitivity reactions mediated by various allergens. The most common allergic diseases include allergic rhinitis, allergic asthma, allergic dermatitis, and allergic conjunctivitis. The incidence of allergic diseases has been increasing in the recent past, and allergen avoidance and adoption of desensitization treatment can significantly decrease the incidence of allergic diseases. Previous studies have explored the association between vitamin A supplementation and allergic diseases; however, the results are inconsistency. The aim of the present study was to evaluate the association between vitamin A supplementation and allergic diseases, with a focus on atopy and wheezing.

METHODS

Articles reporting randomized controlled trials (RCTs) on the association of vitamin A supplementation and allergic diseases were retrieved from PubMed, Embase, Web of science, and China National Knowledge Infrastructure database from inception of to November 15, 2021. STATA 12.0 software was used for meta-analysis, sensitivity analysis and analysis of publication bias.

RESULTS

Seven studies comprising 2201 participants met the inclusion criteria and were included in the meta-analysis. The findings showed that vitamin A supplementation was associated with increased risk of atopy in young females compared with the placebo [RR = 1.70, 95% confidence interval (1.20, 2.41), P = 0.171, I 2 = 43.4% fixed effect model]. The frequency of delayed atopy among adults was associated with vitamin A supplementation (MD = 0.46, 95% CI = 0.04, 0.88). Analysis showed no significant association between vitamin A supplementation with incidence of wheezing in children [RR = 1.40, 95% CI (0.49, 3.98), P = 0.018, I 2 = 82.1% random effect model]. Sensitivity and publication bias analysis showed that each individual study did not affect the combined results and there was no significant publication bias among the studies.

CONCLUSION

The findings showed that vitamin A supplementation is associated with increased risk of atopy but no correlation was observed with the incidence of wheezing. The results of this meta-analysis provide evidence for effective management of fibrosis. More studies should be conducted to verify the results.

(R)Evolution in Allergic Rhinitis Add-On Therapy: From Probiotics to Postbiotics and Parabiotics

Starting from the “Hygiene Hypothesis” to the “Microflora hypothesis” we provided an overview of the symbiotic and dynamic equilibrium between microbiota and the immune system, focusing on the role of dysbiosis in atopic march, particularly on allergic rhinitis. The advent of deep sequencing technologies and metabolomics allowed us to better characterize the microbiota diversity between individuals and body sites. Each body site, with its own specific environmental niches, shapes the microbiota conditioning colonization and its metabolic functionalities. The analysis of the metabolic pathways provides a mechanistic explanation of the remote mode of communication with systems, organs, and microflora of other body sites, including the ecosystem of the upper respiratory tract. This axis may have a role in the development of respiratory allergic disease. Notably, the microbiota is significant in the development and maintenance of barrier function; influences hematopoiesis and innate immunity; and shows its critical roles in Th1, Th2, and Treg production, which are necessary to maintain immunological balance and promote tolerance, taking part in every single step of the inflammatory cascade. These are microbial biotherapy foundations, starting from probiotics up to postbiotics and parabiotics, in a still-ongoing process. When considering the various determinants that can shape microbiota, there are several factors to consider: genetic factors, environment, mode of delivery, exposure to antibiotics, and other allergy-unrelated diseases. These factors hinder the engraftment of probiotic strains but may be upgradable with postbiotic and parabiotic administration directly on molecular targets. Supplementation with postbiotics and parabiotics could represent a very exciting perspective of treatment, bypassing probiotic limitations. At present, this avenue remains theoretical and to be explored, but it will certainly be a fascinating path to follow.

Temporal changes of the respiratory microbiota as cats transition from health to experimental acute and chronic allergic asthma

In humans, deviation from a core airway microbiota may predispose to development, exacerbation, or progression of asthma. We proposed to describe microbiota changes using 16 rRNA sequencing in samples from the upper and lower airways, and rectal swabs of 8 cats after experimental induction of asthma using Bermuda grass allergen, in acute (6 weeks) and chronic (36 weeks) stages. We hypothesized that asthma induction would decrease richness and diversity and alter microbiota composition and structure in the lower airways, without significantly impacting other sites. After asthma induction, richness decreased in rectal (p = 0.014) and lower airway (p = 0.016) samples. B diversity was significantly different between health and chronic asthma in all sites, and between all time points for lower airways. In healthy lower airways Pseudomonadaceae comprised 80.4 ± 1.3% whereas Sphingobacteriaceae and Xanthobacteraceae predominated (52.4 ± 2.2% and 33.5 ± 2.1%, respectively), and Pseudomonadaceae was absent, in 6/8 cats with chronic asthma. This study provides evidence that experimental induction of asthma leads to dysbiosis in the airways and distant sites in both the acute and chronic stages of disease. This article has been published alongside "Respiratory dysbiosis in cats with spontaneous allergic asthma" (1).

Probiotics Function in Preventing Atopic Dermatitis in Children

Atopic dermatitis (AD) is a chronic inflammatory skin disorder characterized by relapsing eczematous injuries and severe pruritus. In the last few years, the AD prevalence has been increasing, reaching 20% in children and 10% in adults in high-income countries. Recently, the potential role of probiotics in AD prevention has generated considerable interest. As many clinical studies show, the gut microbiota is able to modulate systemic inflammatory and immune responses influencing the development of sensitization and allergy. Probiotics are used increasingly against AD. However, the molecular mechanisms underlying the probiotics mediated anti-allergic effect remain unclear and there is controversy about their efficacy. In this narrative review, we examine the actual evidence on the effect of probiotic supplementation for AD prevention in the pediatric population, discussing also the potential biological mechanisms of action in this regard.

Do Probiotics in Pregnancy Reduce Allergies and Asthma in Infancy and Childhood? A Systematic Review

The maternal immune system is very important in the development of the foetal immune system. Probiotics have been shown to help regulate immune responses. Therefore, it is possible that the administration of probiotics to pregnant women could influence the development of the foetal immune system, reducing the likelihood of infants and children developing an allergic condition. The aim of this research was to conduct a systematic review to determine whether administering probiotics to pregnant women can reduce the incidence of allergic disease in their children. Medline, CINAHL and Embase databases were searched for randomised controlled trials (RCTs) that compared supplementation of probiotics to pregnant women to a placebo control and recorded the presentation of allergic conditions in their children. Data extracted from the study reports included their characteristics and findings. Study quality and risk of bias were assessed. From a total of 850 articles identified in the search, 6 were eligible for inclusion in this review. Two studies found no effect of maternal probiotics on the outcomes measured, two studies found that the incidence of eczema or atopic dermatitis (AD) was reduced by maternal probiotics, one study found no effect on the overall incidence of atopic sensitisation, but a reduction in a subgroup of children at high hereditary risk of allergic disease, and one study found no effect in an intention to treat analysis, but a reduction in AD in complete case analysis. The results of these studies are inconsistent but demonstrate that probiotics may have the potential to reduce infant allergies when administered prenatally, particularly in children at high risk of allergy development. There is a need for further larger-scale studies to be performed in order to provide a more definitive answer. Such studies should focus on at-risk groups.

Polymorphic Variants of Interleukin-13 R130Q and Interleukin-4 T589C in Children with and without Cow's Milk Allergy

Cow’s milk allergy (CMA) is one of the most frequent types of food allergy. The aim of the study was to investigate whether IL-13 R130Q and IL-4 T589C polymorphisms are associated with the risk of CMA in young Ukrainian children. A total of 120 children (age range: 1−3 years) participated in the study and were divided into two groups: CMA (n = 60) and healthy controls (CNT, n = 60). The CMA group had two subgroups: specific oral tolerance induction (SOTI, n = 30) and milk elimination diet (MED, n = 30). The CNT group had two subgroups: positive family history of allergy (+FHA, n = 24) and negative family history of allergy (−FHA, n = 36). In the CMA group, molecular genetic testing of CC, CT, and TT genotypes of single nucleotide IL-4 T589C gene polymorphisms showed significantly higher rates of the CC genotype compared to healthy controls (92.2% vs. 58.8%; p < 0.01). In the CMA group, molecular genetic testing of GG, GA, and AA genotypes of single nucleotide IL-13 R130Q gene polymorphisms showed significantly higher rates of GA and AA polymorphic locus genotypes compared to healthy controls (43.5% vs. 22.4%, p < 0.05 and 8.7% vs. 0%, p < 0.05, respectively). In future studies, the genotypic and allelic distribution of these polymorphic variants will be determined in children with CMA and healthy children.

New Directions in Understanding Atopic March Starting from Atopic Dermatitis

Recent evidence showed that the postulated linear progression of the atopic march, from atopic dermatitis to food and respiratory allergies, does not capture the heterogeneity of allergic phenotypes, which are influenced by complex interactions between environmental, genetic, and psychosocial factors. Indeed, multiple atopic trajectories are possible in addition to the classic atopic march. Nevertheless, atopic dermatitis is often the first manifestation of an atopic march. Improved understanding of atopic dermatitis pathogenesis is warranted as this could represent a turning point in the prevention of atopic march. In this review, we outline the recent findings on the pathogenetic mechanisms leading to atopic dermatitis that could be targeted by intervention strategies for the prevention of atopic march.