Does diversity of environmental microbial exposure matter for the occurrence of allergy and asthma?

Prenatal and childhood infections: implications for the development and treatment of childhood asthma

Bacterial and viral infections occur early and recurrently in life and thereby impose a substantial disease burden. Besides causing clinical symptoms, a potential role of infection in the development of the asthma syndrome later in life has also been suggested. However, whether bacterial and viral infections unmask host factors in children at risk of asthma or whether they directly cause asthma remains unclear; both viewpoints could be justified, but the underlying mechanisms are complex and poorly understood. Recently, the role of the bacterial microbiome has been emphasised. But data are still sparse and future studies are needed for definitive conclusions to be made. In this Review, we discuss present knowledge of viruses and bacteria that infect and colonise the respiratory tract and mucosal surfaces, including their timepoint of action, host factors related to infection, and their effect on childhood asthma. Childhood asthma could be the result of a combination of altered host susceptibility and infectious agents.

Toll-like receptors link atopic march to the hygiene hypothesis

In recent decades, the prevalence of atopic diseases has increased substantially worldwide, but their molecular pathologies are now being elucidated. The report by Haapakoski et al. in this issue suggests that the manner in which the immune system encounters an allergen is key to the subsequent polarization of its responses, and the presence of microbial ligands appears to be important in this process. Data in this report provide further proof of the hygiene hypothesis that combine it with known features of the atopic march.

Current and future directions in pediatric allergic rhinitis

BACKGROUND

Allergic rhinitis (AR) is a common pediatric problem that significantly affects sleep, learning, performance, and quality of life. In addition, it is associated with significant comorbidities and complications.

OBJECTIVE

The aim was to provide an update on the epidemiology, comorbidities, pathophysiology, current treatment, and future direction of pediatric AR.

METHODS

Literature reviews in each of these areas were conducted, and the results were incorporated.

RESULTS

The prevalence of AR is increasing in the pediatric population and is associated with significant morbidity, comorbidities, and complications. The mainstay of current treatment strategies includes allergen avoidance, pharmacotherapy, and allergen specific immunotherapy.

CONCLUSIONS

In the future, diagnosis will be improved by microarrayed recombinant allergen testing and therapy will be expanded to include emerging treatments such as sublingual immunotherapy and combination products.

Staphylococcal enterotoxin specific IgE and asthma: a systematic review and meta-analysis

BACKGROUND

Recent literature suggests that Staphylococcal enterotoxin specific IgE may be a risk factor for asthma.

OBJECTIVE

To investigate the associations between Staphylococcal enterotoxin sensitization and asthma.

METHODS

A systematic review and meta-analysis was performed for relevant case-control or population-based studies, published in the peer-reviewed journals until February 2013. Data were extracted on study designs, subjects, definitions and the prevalence of Staphylococcal enterotoxin sensitization.

RESULTS

A total of 683 studies were initially identified, of which 7 studies finally met the inclusion criteria (5 case-control and 2 population-based studies). All the included studies reported higher prevalence of the sensitization in asthmatics than in controls, despite clinical and methodological heterogeneity. In a meta-analysis, the pooled odds ratio of the sensitization for asthma was 2.95 (95% confidence intervals 2.28-3.82).

CONCLUSION

Staphylococcal enterotoxin sensitization was significantly associated with asthma. The mechanisms of associations warrant further elucidation.

Microbes and mucosal immune responses in asthma

The substantial increase in the worldwide prevalence of asthma and atopy has been attributed to lifestyle changes that reduce exposure to bacteria. A recent insight is that the largely bacterial microbiome maintains a state of basal immune homoeostasis, which modulates immune responses to microbial pathogens. However, some respiratory viral infections cause bronchiolitis of infancy and childhood wheeze, and can exacerbate established asthma; whereas allergens can partly mimic infectious agents. New insights into the host’s innate sensing systems, combined with recently developed methods that characterise commensal and pathogenic microbial exposure, now allow a unified theory for how microbes cause mucosal inflammation in asthma. The respiratory mucosa provides a key microbial interface where epithelial and dendritic cells interact with a range of functionally distinct lymphocytes. Lymphoid cells then control a range of pathways, both innate and specific, which organise the host mucosal immune response. Fundamental to innate immune responses to microbes are the interactions between pathogen-associated molecular patterns and pattern recognition receptors, which are associated with production of type I interferons, proinflammatory cytokines, and the T-helper-2 cell pathway in predisposed people. These coordinated, dynamic immune responses underlie the differing asthma phenotypes, which we delineate in terms of Seven Ages of Asthma. An understanding of the role of microbes in the atopic march towards asthma, and in causing exacerbations of established asthma, provides the rationale for new specific treatments that can be assessed in clinical trials. On the basis of these new ideas, specific host biomarkers might then allow personalised treatment to become a reality for patients with asthma.

Advances in adult asthma diagnosis and treatment in 2012: potential therapeutics and gene-environment interactions

In the Journal of Allergy and Clinical Immunology in 2012, research reports related to asthma in adults clustered around mechanisms of disease, with a special focus on their potential for informing new therapies. There was also consideration of the effect of the environment on health from pollution, climate change, and epigenetic influences, underlining the importance of understanding gene-environment interactions in the pathogenesis of asthma and response to treatment.

Genetic variation of ITGB3 is associated with asthma in Chinese Han children

Previous studies have demonstrated that integrins are involved in the aetiology of asthma. Several single-nucleotide polymorphisms (SNPs) in the integrin β3 (ITGB3) gene are significantly associated with asthma in Western populations. Given the important roles of environmental exposures in the development of asthma, we evaluated the associations between six SNPs in ITGB3 and asthma in Chinese Han children. A total of 321 unrelated Chinese children with asthma and 315 healthy children were recruited for the study. SNP genotyping was performed by high-resolution melting analysis (HRM). The selected SNPs were well genotyped by HRM, and SNP rs3809865 in the 3′ untranslated region (3′UTR) of ITGB3 was found to be strongly associated with asthma (adjusted p = 0.004). The minor allele of rs3809865 showed a protective effect against asthma (OR: 0.59; 95% CI: 0.43–0.8). The seed regions of two miRNAs (hsa-mir-124 and hsa-mir-506) were predicted to bind to the sequence containing rs3809865 by TargetScan and PITA. Luciferase reporter assays demonstrated that the T allele of rs3809865 was more efficiently targeted by hsa-mir-124 than was the A allele, which suggested that rs3809865 could affect the binding of hsa-mir-124 to ITGB3. Furthermore, the transfection of A549 cells with hsa-mir-124 resulted in the downregulation of ITGB3 expression. Our results revealed that rs3809865 was significantly associated with asthma due to its effect on the binding of hsa-mir-124 to ITGB3.

Lipopolysaccharide inhibits Th2 lung inflammation induced by house dust mite allergens in mice

The complex biology of asthma compels the use of more relevant human allergens, such as house dust mite (HDM), to improve the translation of animal models into human asthma. LPS exposure is associated with aggravations of asthma, but the mechanisms remain unclear. Here, we studied the effects of increasing LPS doses on HDM-evoked allergic lung inflammation. To this end, mice were intranasally sensitized and challenged with HDM with or without increasing doses of LPS (0.001-10 μg). LPS dose-dependently inhibited HDM-induced eosinophil recruitment into the lungs and mucus production in the airways. LPS attenuated the production of Th2 cytokines (IL-4, IL-5, IL-10, and IL-13) in HDM-challenged lungs, while enhancing the HDM-induced release of IL-17, IL-33, IFN-γ, and TNF-α. The shift toward a Th1 inflammatory response was further illustrated by predominant neutrophilic lung inflammation after LPS administration at higher doses. LPS did not influence HDM-induced plasma IgE concentrations. Although LPS did not significantly affect the activation of coagulation or complement in HDM-challenged lungs, it reduced HDM-initiated endothelial cell activation. This study is the first to provide insights into the effects of LPS in an allergic lung inflammation model making use of a clinically relevant allergen without a systemic adjuvant, revealing that LPS dose-dependently inhibits HDM-induced pulmonary Th2 responses.

Advances in pediatric asthma in 2012: moving toward asthma prevention

Last year's "Advances in pediatric asthma: moving forward" concluded the following: "Now is also the time to utilize information recorded in electronic medical records to develop innovative disease management plans that will track asthma over time and enable timely decisions on interventions in order to maintain control that can lead to disease remission and prevention." This year's summary will focus on recent advances in pediatric asthma on modifying disease activity, preventing asthma exacerbations, managing severe asthma, and risk factors for predicting and managing early asthma, as indicated in Journal of Allergy and Clinical Immunology publications in 2012. Recent reports continue to shed light on methods to improve asthma management through steps to assess disease activity, tools to standardize outcome measures in asthma, genetic markers that predict risk for asthma and appropriate treatment, and interventions that alter the early presentation of asthma to prevent progression. We are well on our way to creating a pathway around wellness in asthma care and also to use new tools to predict the risk for asthma and take steps to not only prevent asthma exacerbations but also to prevent the early manifestations of the disease and thus prevent its evolution to severe asthma.

Allergic airway diseases in childhood - marching from epidemiology to novel concepts of prevention

In the past years, a wide range of epidemiological, clinical, and experimental studies have produced remarkable advances in the field of respiratory allergies in childhood. By the recent investigations on epidemiological trends, risk factors, and prevention of asthma and allergic rhinitis, various exiting concepts have been challenged, and novel innovative approaches have been developed. Pediatric Allergy and Immunology (PAI), with a number of highly relevant contributions between 2010 and 2012, has become an important forum in this area. The prevalence of asthma in some developed countries may have reached a plateau, while in developing countries, where the prevalence was previously low, allergic diseases are still on the increase. A wide array of risk and protective factors, including hygiene, infections, outdoor and indoor air pollution, allergen exposure, breast-feeding practices, nutrition, and obesity, play a multifaceted role in shaping the observed worldwide trends of respiratory allergies. Under the guidance of recent research, prediction and prevention strategies in the clinical practice are progressively changing, the focus moving away from avoidance of allergen exposure and toward tolerance induction.

Microbial regulation of allergic responses to food

The incidence of food allergy in developed countries is rising at a rate that cannot be attributed to genetic variation alone. In this review, we discuss the environmental factors that may contribute to the increasing prevalence of potentially fatal anaphylactic responses to food. Decreased exposure to enteric infections due to advances in vaccination and sanitation, along with the adoption of high-fat (Western) diets, antibiotic use, Cesarean birth, and formula feeding of infants, have all been implicated in altering the enteric microbiome away from its ancestral state. This collection of resident commensal microbes performs many important physiological functions and plays a central role in the development of the immune system. We hypothesize that alterations in the microbiome interfere with immune system maturation, resulting in impairment of IgA production, reduced abundance of regulatory T cells, and Th2-skewing of baseline immune responses which drive aberrant responses to innocuous (food) antigens.

Asthma: a chronic infectious disease?

There are increasing data to support the "hygiene" and "microbiota" hypotheses of a protective role of infections in modulating the risk of subsequent development of asthma. There is less evidence that respiratory infections can actually cause the development of asthma. There is some evidence that rhinovirus respiratory infections are associated with the development of asthma, particularly in childhood, whereas these infections in later life seem to have a weaker association with the development of asthma. The role of bacterial infections in chronic asthma remains unclear. This article reviews the available evidence indicating that asthma may be considered as a chronic infectious disease.