Endotoxin exposure and childhood wheeze and asthma: a meta-analysis of observational studies

The microbiome: an integral player in immune homeostasis and inflammation in the respiratory tract

The last decade of microbiome research has highlighted its fundamental role in systemic immune and metabolic homeostasis. The microbiome plays a prominent role during gestation and into early life, when maternal lifestyle factors shape immune development of the newborn. Breast milk further shapes gut colonization, supporting the development of tolerance to commensal bacteria and harmless antigens while preventing outgrowth of pathogens. Environmental microbial and lifestyle factors that disrupt this process can dysregulate immune homeostasis, predisposing infants to atopic disease and childhood asthma. In health, the low-biomass lung microbiome, together with inhaled environmental microbial constituents, establishes the immunological set point that is necessary to maintain pulmonary immune defense. However, in disease perturbations to immunological and physiological processes allow the upper respiratory tract to act as a reservoir of pathogenic bacteria, which can colonize the diseased lung and cause severe inflammation. Studying these host-microbe interactions in respiratory diseases holds great promise to stratify patients for suitable treatment regimens and biomarker discovery to predict disease progression. Preclinical studies show that commensal gut microbes are in a constant flux of cell division and death, releasing microbial constituents, metabolic by-products, and vesicles that shape the immune system and can protect against respiratory diseases. The next major advances may come from testing and utilizing these microbial factors for clinical benefit and exploiting the predictive power of the microbiome by employing multiomics analysis approaches.

Effects of indoor air quality and home environmental characteristics on allergic diseases among preschool children in the Greater Taipei Area

Indoor air quality and home environmental characteristics are potential factors associated with the onset and exacerbation of allergic diseases. Our study examined the effects of these factors on allergic diseases (i.e., asthma, allergic rhinitis, allergic conjunctivitis, and atopic dermatitis) among preschool children. We recruited a total of 120 preschool children from an ongoing birth cohort study in the Greater Taipei Area. A comprehensive environmental evaluation was conducted at each participant's residence and included measurements of indoor and outdoor air pollutants, fungal spores, endotoxins, and house dust mite allergens. A structured questionnaire was used to collect information on the allergic diseases and home environments of participants. Land-use characteristics and points of interest in the surrounding area of each home were analyzed. Other covariates were obtained from the cohort data. Multiple logistic regressions were used to examine the relationships between allergic diseases and covariates. We observed that all mean indoor air pollutant levels were below Taiwan's indoor air quality standards. After adjustment for covariates, the total number of fungal spores and the ozone, Der f 1, and endotoxin levels were significantly associated with increased risks of allergic diseases. Biological contaminants more significantly affected allergic diseases than other pollutants. Moreover, home environmental characteristics (e.g., living near power facilities and gas stations) were associated with an increased risk of allergic diseases. Regular and proper home sanitation is recommended to prevent the accumulation of indoor pollutants, especially biological contaminants. Living away from potential sources of pollution is also crucial for protecting the health of children.

What Have Mechanistic Studies Taught Us About Childhood Asthma?

Childhood asthma is a chronic heterogeneous syndrome consisting of different disease entities or phenotypes. The immunologic and cellular processes that occur during asthma development are still not fully understood but represent distinct endotypes. Mechanistic studies have examined the role of gene expression, protein levels, and cell types in early life development and the manifestation of asthma, many under the influence of environmental stimuli, which can be both protective and risk factors for asthma. Genetic variants can regulate gene expression, controlled partly by different epigenetic mechanisms. In addition, environmental factors, such as living space, nutrition, and smoking, can contribute to these mechanisms. All of these factors produce modifications in gene expression that can alter the development and function of immune and epithelial cells and subsequently different trajectories of childhood asthma. These early changes in a partially immature immune system can have dramatic effects (e.g., causing dysregulation), which in turn contribute to different disease endotypes and may help to explain differential responsiveness to asthma treatment. In this review, we summarize published studies that have aimed to uncover distinct mechanisms in childhood asthma, considering genetics, epigenetics, and environment. Moreover, a discussion of new, powerful tools for single-cell immunologic assays for phenotypic and functional analysis is included, which promise new mechanistic insights into childhood asthma development and therapeutic and preventive strategies.

The Environmental Microbiome, Allergic Disease, and Asthma

The environmental microbiome represents the entirety of the microbes and their metabolites that we encounter in our environments. A growing body of evidence supports the role of the environmental microbiome in risk for and severity of allergic diseases and asthma. The environmental microbiome represents a ubiquitous, lifelong exposure to non-self antigens. During the critical window between birth and 1 year of life, interactions between our early immune system and the environmental microbiome have 2 consequences: our individual microbiome is populated by environmental microbes, and our immune system is trained regarding which antigens to tolerate. During this time, a diversity of exposures appears largely protective, dramatically decreasing the risk of developing allergic diseases and asthma. As we grow older, our interactions with the environmental microbiome change. While it continues to exert influence over the composition of the human microbiome, the environmental microbiome becomes increasingly a source for antigenic stimulation and infection. The same microbial exposure protective against disease development may exacerbate disease severity. Although much has been learned about the importance of the environmental microbiome in allergic disease, much more remains to be understood about these complicated interactions between our environment, our microbiome, our immune system, and disease.

Epithelial barrier hypothesis: Effect of the external exposome on the microbiome and epithelial barriers in allergic disease

Environmental exposure plays a major role in the development of allergic diseases. The exposome can be classified into internal (e.g., aging, hormones, and metabolic processes), specific external (e.g., chemical pollutants or lifestyle factors), and general external (e.g., broader socioeconomic and psychological contexts) domains, all of which are interrelated. All the factors we are exposed to, from the moment of conception to death, are part of the external exposome. Several hundreds of thousands of new chemicals have been introduced in modern life without our having a full understanding of their toxic health effects and ways to mitigate these effects. Climate change, air pollution, microplastics, tobacco smoke, changes and loss of biodiversity, alterations in dietary habits, and the microbiome due to modernization, urbanization, and globalization constitute our surrounding environment and external exposome. Some of these factors disrupt the epithelial barriers of the skin and mucosal surfaces, and these disruptions have been linked in the last few decades to the increasing prevalence and severity of allergic and inflammatory diseases such as atopic dermatitis, food allergy, allergic rhinitis, chronic rhinosinusitis, eosinophilic esophagitis, and asthma. The epithelial barrier hypothesis provides a mechanistic explanation of how these factors can explain the rapid increase in allergic and autoimmune diseases. In this review, we discuss factors affecting the planet's health in the context of the 'epithelial barrier hypothesis,' including climate change, pollution, changes and loss of biodiversity, and emphasize the changes in the external exposome in the last few decades and their effects on allergic diseases. In addition, the roles of increased dietary fatty acid consumption and environmental substances (detergents, airborne pollen, ozone, microplastics, nanoparticles, and tobacco) affecting epithelial barriers are discussed. Considering the emerging data from recent studies, we suggest stringent governmental regulations, global policy adjustments, patient education, and the establishment of individualized control measures to mitigate environmental threats and decrease allergic disease.

Effects of early-life exposure to dust mite allergen and endotoxin on the development of asthma and wheezing: The Japan Environment and Children's Study

BACKGROUND

The effects of early-life exposure to house dust mite allergen and endotoxin on the development of asthma are unclear in the literature. We investigated the association of early-life exposure (0-36 months old) to house dust mite allergen and endotoxin with asthma incidence.

METHODS

In this novel, large-scale, nationwide birth cohort study, 5017 participants were randomly selected from those who met the eligibility criteria. House dust was vacuum-sampled from the children's mattresses within homes and assayed for the presence of dust mite allergen (Der 1) and endotoxin. The participants were classified into four quartiles (Q1-Q4) according to exposure levels. We defined the incidence of asthma and wheezing using questionnaires at 12, 24, and 36 months old. Odds ratios (ORs) of the incidence of asthma and wheezing by age in Der 1 and endotoxin exposure level were estimated using logistic regression.

RESULTS

The cumulative incidence rates of asthma and wheezing during 0-36 months were 10.4% and 38.1%, respectively. Significant ORs were observed in asthma onset during 12-24 months old, asthma onset during 24-36 months old, and wheezing onset during 0-12 months old in the Q4 Der 1 group. In the Q4 endotoxin group, significant positive associations between endotoxin exposure and asthma (OR 2.00, 95% confidence interval [CI]: 1.03-3.85) and wheezing (OR 1.78, 95% CI: 1.01-3.12) onset during 24-36 months old were found.

CONCLUSIONS

Our results indicated that high levels of early-life exposure to Der 1 and endotoxin in mattresses may be involved in the development of asthma.

Association of indoor microbial aerosols with respiratory symptoms among under-five children: a systematic review and meta-analysis

BACKGROUND

Despite the recognition of the importance of indoor microbial exposures on children's health, the role of different microbial agents in development and aggravation of respiratory symptoms and diseases is only poorly understood. This study aimed to assess whether exposure to microbial aerosols within the indoor environment are associated with respiratory symptoms among children under-5 years of age.

METHODS

A systematic literature search was conducted on PubMed, Web of Science, GreenFILE, ScienceDirect, EMBASE and Cochrane library through February 2020. Studies that investigated the exposure-response relationship between components of the indoor microbial communities and respiratory symptoms among under-five children were eligible for inclusion. A random-effect meta-analysis was applied to estimate pooled relative risk (RR) and 95% confidence interval (CI) for study specific high versus low microbial exposures. The potential effect of individual studies on the overall estimate was evaluated using leave-one-out analysis, while heterogeneity was evaluated by I² statistics using RevMan 5.3.

RESULTS

Fifteen studies were eligible for inclusion in a meta-analysis. The pooled risk estimate suggested that increased microbial exposure was associated with an increased risk of respiratory symptoms [pooled relative risk (RR): 1.24 (1.09, 1.41), P = 0.001]. The association was strongest with exposure to a combination of Aspergillus, Penicillium, Cladosporium and Alternaria species [pooled RR: 1.73 (1.30, 2.31), P = 0.0002]. Stratified analysis revealed an increased risk of wheeze [pooled RR: 1.20 (1.05, 1.37), P = 0.007 and allergic rhinitis [RR: 1.18 (0.94, 1.98), P = 0.16] from any microbial exposure.

CONCLUSIONS

Microbial exposures are, in general, associated with risk of respiratory symptoms. Future studies are needed to study the indoor microbiome more comprehensively, and to investigate the mechanism of these associations.

Exposures in the Indoor Environment and Prevalence of Allergic Conditions in the United States of America

Our study examines the association of the presence of mildew, cockroaches, and pets in homes as well as household dust allergens with the prevalence and/or severity of allergic diseases. No study has concurrently assessed home environment exposures in relation to allergic conditions in the general US population. Data from 5409 participants from the 2005–2006 National Health and Nutrition Examination Survey (NHANES) living in their current homes for ≥one year were analyzed. Multivariate logistic regression analyses between home exposures and allergic diseases prevalence and severity were performed. In adjusted analyses, mildew was associated with higher current asthma, allergies, and allergic rhinitis prevalence; endotoxin, with higher current asthma prevalence; and dust Canis familiaris (Can f) 1, with higher allergic rhinitis prevalence. However, presence of cockroaches and dust Dermatophagoides farinae (Der f) 1 were associated, respectively, with lower current asthma and allergies prevalence. Presence of mildew, dust Der f1, Dermatophagoides pteronyssinus (Der p) 1, Felis domesticus (Fel d) 1, and endotoxin were all associated with asthma and/or wheeze severity. Non-atopic asthma was more frequent with mildew and/or musty smell dust and higher dust Fel d1 concentration, while atopic asthma was more prevalent with higher Can f1 and endotoxin concentrations in dust. This study confirms previous relationships and reports novel associations, generating hypotheses for future research.

The intersect of genetics, environment, and microbiota in asthma-perspectives and challenges

In asthma, a significant portion of the interaction between genetics and environment occurs through microbiota. The proposed mechanisms behind this interaction are complex and at times contradictory. This review covers recent developments in our understanding of this interaction: the "microbial hypothesis" and the "farm effect"; the role of endotoxin and genetic variation in pattern recognition systems; the interaction with allergen exposure; the additional involvement of host gut and airway microbiota; the role of viral respiratory infections in interaction with the 17q21 and CDHR3 genetic loci; and the importance of in utero and early-life timing of exposures. We propose a unified framework for understanding how all these phenomena interact to drive asthma pathogenesis. Finally, we point out some future challenges for continued research in this field, in particular the need for multiomic integration, as well as the potential utility of asthma endotyping.

Indoor Microbial Exposures and Chronic Lung Disease: From Microbial Toxins to the Microbiome

Effects of environmental microbial exposures on human health have long been of interest. Microbes were historically assumed to be harmful, but data have suggested that microbial exposures can modulate the immune system. We focus on the effects of indoor environmental microbial exposure on chronic lung diseases. We found contradictory data in bacterial studies using endotoxin as a surrogate for bacterial exposure. Contradictory data also exist in studies of fungal exposure. Many factors may modulate the effect of environmental microbial exposures on lung health, including coexposures. Future studies need to clarify which method of assessing environmental microbial exposures is most relevant.

The effect of the indoor environment on wheeze- and sleep-related symptoms in young Indian children

Background

Environmental exposures have a significant effect on respiratory and sleep symptoms in young children. Although the effect of air pollution on the respiratory symptoms in young children is well-established, less is known about the effect of household environmental characteristics and practices on wheeze and sleep concerns.

Aims

The aim of this pilot study is to explore the association between household environmental characteristics and practices with the symptoms of wheezing and sleep concerns in the past year in a convenience sample of young Indian children.

Materials and Methods

A detailed questionnaire about the child's home environment and respiratory and sleep symptoms was administered to the caregivers of 190 outpatients aged between 6 months and 5 years old at a teaching hospital.

Results

Indoor environmental characteristics and cleaning techniques were analyzed for the association with wheeze and sleep disorders. Half (50%) of the cohort had the symptoms of wheezing and 21% had occasional or frequent sleep concerns. Sleeping with a stuffed toy was significantly associated with both wheezing and sleep concerns (P = 0.05).

Conclusions

: Sleeping with a stuffed toy was a risk factor for wheeze and a risk factor for sleep disorders independent of wheeze.

House dust endotoxin, asthma and allergic sensitization through childhood into adolescence

Background

House dust endotoxin may have beneficial effects on allergic sensitization and asthma in children. Evidence is scarce for adolescents and most studies so far have been cross‐sectional and limited to a single exposure measurement.

Objective

We assessed associations of house dust endotoxin with asthma and allergic sensitization from birth to age 17 years longitudinally taking into account exposure early in life and at primary school age.

Methods

We used data of 854 participants of the prospective Dutch PIAMA birth cohort study with house dust endotoxin measurements at 3 months and/or 5‐6 years and data on asthma and/or allergic sensitization from at least one of 11 follow‐ups until age 17. We assessed overall and age‐specific associations of the prevalence of asthma and sensitization with mattress and living room floor dust concentrations (per gram of dust) and loads (per m² of sampling surface).

Results

Higher living room floor dust endotoxin concentrations at 3 months were associated with lower odds of asthma until age 4 [odds ratio (95% confidence interval) ranging from 0.70 (0.51‐0.97) at age 1 to 0.76 (0.57‐1.00) at age 3 per interquartile range increase], but not thereafter in children of allergic mothers. Higher living room floor dust endotoxin at 5‐6 years was associated with higher odds of sensitization at 8‐16 years [eg odds ratio (95% confidence interval) 1.70 (1.17‐2.47) per interquartile range increase in endotoxin load].

Conclusions and clinical relevance

House dust endotoxin may have beneficial effects on asthma in preschool children of allergic mothers, which do not persist into adolescence. Beneficial associations with allergic sensitization could not be confirmed.

Endotoxin clustering with allergens in house dust and asthma outcomes in a U.S. national study

BACKGROUND

Endotoxin is ubiquitous in the environment, but its clustering with indoor allergens is not well characterized. This study examined the clustering patterns of endotoxin with allergens in house dust and their association with asthma outcomes.

METHODS

We analyzed data from 6963 participants of the 2005-2006 National Health and Nutrition Examination Survey. House dust sampled from bedroom floor and bedding was evaluated for endotoxin and allergens from fungi, cockroach, dog, cat, mites, and rodents. Two-step cluster analysis and logistic regressions were performed to identify the clustering patterns and their associations with current asthma and wheeze in the past 12 months, adjusting for covariates.

RESULTS

Of the homes, 17.8% had low endotoxin and allergen levels in house dust (Cluster 1). High endotoxin level clustered with Alternaria and pet allergens in the homes of participants with a high socioeconomic status who own pets (Cluster 2) (48.9%). High endotoxin clustered with Aspergillus, dust mites, cockroach, and rodent allergens in the homes of participants with low socioeconomic status (Cluster 3) (33.3%). Compared to Cluster 1, Cluster 2 was associated with higher asthma prevalence (OR 1.42, 95% CI: 1.06-1.91) and wheeze (OR 1.32, 95% CI: 1.07-1.63). Cluster 3 was positively associated with wheeze only in participants sensitized to inhalant allergens (OR 1.42, 95% CI: 1.06-1.91) or exposed to tobacco smoke (OR 1.72, 95% CI: 1.15-2.60).

CONCLUSIONS

The clustering of endotoxin with allergens in dust from homes with pets or of people with low socioeconomic status is associated with asthma and wheeze.

Synergistic Association of House Endotoxin Exposure and Ambient Air Pollution with Asthma Outcomes

Rationale: House endotoxin and ambient air pollution are risk factors for asthma; however, the effects of their coexposure on asthma are not well characterized.Objectives: To examine potential synergistic associations of coexposure to house dust endotoxin and ambient air pollutants with asthma outcomes.Methods: We analyzed data of 6,488 participants in the National Health and Nutrition Examination Survey 2005-2006. Dust from bedding and bedroom floor was analyzed for endotoxin content. The Community Multiscale Air Quality Modeling System (CMAQ) and Downscaler Model data were used to determine annual average particulate matter ≤2.5 μm in aerodynamic diameter (PM_2.5), ozone (O₃), and nitrogen dioxide (NO₂) exposures at participants' residential locations. The associations of the coexposures with asthma outcomes were assessed and tested for synergistic interaction.Measurements and Main Results: In adjusted analysis, PM_2.5 (CMAQ) (odds ratio [OR], 1.12; 95% confidence interval [CI], 1.07-1.18), O₃ (Downscaler Model) (OR, 1.07; 95% CI, 1.02-1.13), and log₁₀ NO₂ (CMAQ) (OR, 3.15; 95% CI, 1.33-7.45) were positively associated with emergency room visits for asthma in the past 12 months. Coexposure to elevated concentrations of house dust endotoxin and PM_2.5 (CMAQ) was synergistically associated with the outcome, increasing the odds by fivefold (OR, 5.01; 95% CI, 2.54-9.87). A synergistic association was also found for coexposure to higher concentrations of endotoxin and NO₂ in children (OR, 3.45; 95% CI, 1.65-7.18).Conclusions: Coexposure to elevated concentrations of residential endotoxin and ambient PM_2.5 in all participants and NO₂ in children is synergistically associated with increased emergency room visits for asthma. Therefore, decreasing exposure to both endotoxin and air pollution may help reduce asthma morbidity.

How a farming environment protects from atopy

It is now well established that the exposure to certain environments such as farms has the potential to protect from the development of allergies later in life. This protection is achieved when repeated exposure to the farming environment occurs early in life, but persists when children spend sufficient amount of time in contact with livestock and hay, and drink unpasteurized milk. The capacity of farm dust to protect from allergy development lies, amongst others, in the microbe composition in the farm. These protective microbes release various metabolites and cell wall components that change farmers' home dust composition, when compared to urbanized home dust. Additionally, they can colonize various barrier sites (skin, lung, intestine) in farmers' children, leading to persistent changes in the way their immune system and their barrier cells respond to environmental allergens.

Primary prevention of keratinocyte carcinoma among outdoor workers, the general population and medical professionals: a systematic review updated for 2019

Worldwide 2-3 million cases of keratinocyte carcinoma (KC) are diagnosed annually. Sun-related knowledge is essential for adequate protection against solar ultraviolet radiation (UVR), the main risk factor for KC. The goal was (i) to provide an updated overview of primary prevention against KC including skin cancer-related knowledge, attitudes and sun protection behaviour (SPB) of outdoor workers, the general population and medical professionals as well as (ii) to evaluate the effectiveness and acceptability of sun protection programmes. We conducted a systematic review of articles indexed for MEDLINE on PubMed using selected MeSH terms and keywords related to the studied topic as well as an extensive hand search of publications between 1 January 2012 and 31 December 2018. We identified 51 relevant cross-sectional studies and 22 interventional studies. Sun-related knowledge and attitude showed substantial differences with some alarming results, including people who had not even heard about skin cancer before. Reported SPB varied enormously between the included studies, with none of the studies providing an overall sufficient SPB in their examined sun protection measures. However, sun protection programmes using new technologies seem to have great potential to increase sun-related knowledge and SPB. In countries worldwide, particularly in those where KC is not yet a public health issue, UVR protection should be promoted by healthcare institutions and authorities, politicians, cancer foundations and dermatologists to increase awareness as well as SPB and to decrease the worldwide burden of KC.

Is childhood wheeze and asthma in Latin America associated with poor hygiene and infection? A systematic review

Introduction

High asthma prevalence in Latin-American cities is thought to be caused by poor hygiene and infections. This contradicts the widely accepted 'hygiene hypothesis' for asthma aetiology.

Methods

Systematic review of observational studies evaluating the association between poor hygiene exposures or infections and asthma/wheeze among Latin-American children aged 4-16 years. MEDLINE, EMBASE, LILACS and CINAHL electronic databases were searched following a predefined strategy to 18 December 2017. We quantified outcomes measured and reported, assessed risk of bias and tabulated the results.

Results

Forty-five studies included: 6 cohort, 30 cross-sectional and 9 case-control studies. 26 cross-sectional studies were school-based surveys (14 of over 3000 children), whereas 5 case-control studies were hospital/health centre-based. Exposures measured and reported varied substantially between studies, and current wheeze was the most common outcome reported. Data showed selective reporting based on statistical significance (P value <0.05): 17/45 studies did not clearly describe the number of exposures measured and 15/45 studies reported on less than 50% of the exposures measured. Most exposures studied did not show an association with wheeze or asthma, except for a generally increased risk associated with acute respiratory infections in early life. Contradictory associations were observed frequently between different studies.

Conclusion

Selective reporting is common in observational studies exploring the association between environmental exposures and risk of wheeze/asthma. This, together with the use of different study outcomes (wheeze/asthma) associated with possibly distinct causal mechanisms, complicates inferences about the role of poor hygiene exposures and childhood infections in explaining asthma prevalence in Latin-American children.

Indoor fungal diversity in primary schools may differently influence allergic sensitization and asthma in children

BACKGROUND

Childhood exposure to microbiologic agents may influence the development of allergic and respiratory diseases. Apart from home, children spend most of their time at school, which represents an environment of significant exposure to indoor air microbes. Therefore, we aimed to assess how the prevalence of allergic sensitization and asthma in schoolchildren is affected by microbiologic exposure within classrooms.

METHODS

Spirometry with bronchodilation, exhaled nitric oxide measurements and skin-prick tests data were retrieved from 858 children aged 8-10 years attending 71 classrooms in 20 primary schools. Air samples were collected in all classrooms using a single-stage microbiologic air impactor through agar plates. Gram-negative endotoxins were collected using flow control pumps and analysed by limulus amebocyte lysate assay. Diversity scores were established as the number of different fungal species found in each classroom.

RESULTS

Classrooms with increased diversity scores showed a significantly lower prevalence of children with atopic sensitization, but not asthma. The risk of sensitization increased with increasing endotoxin exposure in classrooms. Similarly, significantly higher concentrations of Penicillium spp were found in classrooms with a higher number of children with atopic sensitization.

CONCLUSIONS

Although no causal relationships could be established, exposure to higher fungal diversity was protective against allergic sensitization but this was not seen for asthma. In contrast, higher exposure to Gram-negative endotoxins and Penicillium spp in primary school's classrooms was associated with increasing odds of allergic sensitization in children.

Risk and Protective Factors for Childhood Asthma: What Is the Evidence?

To summarize the principal findings on risk and protective factors for childhood asthma, we retrieved systematic reviews on these topics in children (aged 1 to 18 years), up to January 2016, through MEDLINE, EMBASE, CINAHL, SCOPUS, and CDSR. A total of 227 studies were searched from databases. Among those, 41 systematic reviews (SRs) were included: 9 focused on prenatal factors, 5 on perinatal factors, and 27 on postnatal factors. Of these 41 SRs, 83% had good methodological quality, as determined by the Assess Systematic Reviews tool. After reviewing all evidence, parental asthma, prenatal environmental tobacco smoke, and prematurity (particularly very preterm birth) are well-established risk factors for childhood asthma. Current findings do suggest mild-to-moderate causal effects of certain modifiable behaviors or exposures during pregnancy (maternal weight gain or obesity, maternal use of antibiotics or paracetamol, and maternal stress), the perinatal period (birth by Caesarean delivery), or postnatal life (severe respiratory syncytial virus infection, overweight or obesity, indoor exposure to mold or fungi, and outdoor air pollution) on childhood asthma, but this suggestive evidence must be confirmed in interventional studies or (if interventions are not feasible) well-designed prospective studies.

Endotoxin exposure, serum vitamin D, asthma and wheeze outcomes

BACKGROUND

Endotoxin has been shown to induce neutrophilic asthma and wheeze after binding toll-like receptor 4 to produce pro-inflammatory cytokines. Animal models have demonstrated that vitamin D might inhibit lipopolysaccharide-induced cytokines. However, whether endotoxin exposure and serum vitamin D deficiency interact to affect asthma and wheeze in humans has never been investigated in an epidemiological study.

METHODS

Joint associations of house dust endotoxin and vitamin D with asthma and wheeze were examined using logistic regression adjusted for covariates in 5924 US participants of the National Health and Nutrition Examination Survey (NHANES). Interactions were assessed on the multiplicative as well as additive scale using the relative excess risk, the attributable portion due to additive interaction, and the synergy index.

RESULTS

The median endotoxin concentration was 19.1 EU/mg. Prevalence of vitamin D inadequacy (20-30 ng/ml) and deficiency (<20 ng/ml) were respectively 42.9 and 33.4%. The combination of high endotoxin and low vitamin D was associated with current asthma (OR: 1.56, 95% CI: 1.09, 2.23), wheeze in the past 12 months (OR: 1.72, 95% CI: 1.10, 3.71), recurrent wheeze (OR: 1.97, 95% CI: 1.00, 4.00), asthma diagnosis or recurrent wheeze (OR: 1.88, 95% CI: 1.33, 2.66), and current asthma or recurrent wheeze (OR:1.81, 95% CI: 1.23, 2.68) when compared to low endotoxin and normal vitamin D. The interactions between the exposures were not significant on the multiplicative or additive scale for any of the outcomes.

CONCLUSIONS

Combination of high endotoxin exposure and low vitamin D increases the odds of asthma and wheeze, but the exposures do not interact or modify each other's effect in the NHANES cohort.

The microbial environment and its influence on asthma prevention in early life

There is accumulating evidence to suggest that the environmental microbiome plays a significant role in asthma development. The very low prevalence of asthma in populations highly exposed to microbial environments (farm children and Amish populations) highlights its preventive potential. This microbial diversity might be necessary to instruct a well-adapted immune response and regulated inflammatory responses to other inhaled and ingested environmental elements, such as allergens, particles, and viruses. Like the internal gut microbiome, which is increasingly recognized as an important instructor of immune maturation, the external environmental microbiome might shape immune responses on the skin, airway mucosal surfaces, and potentially also the gut early in life. The diversity of the external microbial world will ensure that of the many maladapted pathways leading to asthma development, most, if not all, will be counterbalanced. Likewise, important contributors to asthma, such as allergen sensitization and allergic manifestations early in life, are being suppressed. Thus the facets of innate immunity targeted by microbes and their compounds and metabolites might be the master switch to asthma and allergy protection, which has been found in environments rich in microbial exposures.

Farm environment during infancy and lung function at the age of 31: a prospective birth cohort study in Finland

OBJECTIVES

Farming as an occupation is considered a risk factor for asthma and reduced lung function. By contrast, living on a farm during infancy has been reported to be associated with lower risk of asthma in adulthood. However, little is known about the association between farming environment during infancy and lung function in adulthood. We aimed to study the prospective longitudinal association between farming environment during infancy and lung function in adulthood.

DESIGN

A prospective birth cohort study.

SETTING

Northern Finland.

PARTICIPANTS

5666 participants born in 1966 were followed up at the age of 31 years.

PRIMARY OUTCOME MEASURES

Spirometry at the age of 31 years.

RESULTS

To be born into a farmer's family was associated with higher forced expiratory volume in 1 s (FEV1) (36 mL; 95% CI 6 to 67 mL) and forced vital capacity (FVC) (40 mL; 95% CI 5 to 75 mL) at the age of 31 years. Contact with farm animals during infancy was associated with higher FEV1. No associations were seen with FEV1/FVC (FEV1/FVC ratio). Having dogs in childhood revealed similar associations. There was a suggestive dose-dependent association with the number of animal species during childhood and higher FEV1 and FVC at adulthood, especially among women.

CONCLUSIONS

Farming environment in early life may have a positive impact on lung function in adulthood.

Determinants of house dust, endotoxin, and β-(1→3)-D-glucan in homes of Danish children

Little is known about the geographic variation and determinants of bacterial endotoxin and β-(1,3)-D-glucan in Danish house dust. In a population of 317 children, we: (i) described loads and concentrations of floor dust, endotoxin, and β-(1→3)-D-glucan and (ii) their correlations and (iii) assessed their determinants; (iv) Finally, we compared our findings with previous European studies. Bedroom floor dust was analyzed for endotoxin content by the kinetic limulus amoebocyte lysate assay and for β-(1→3)-D-glucan by the inhibition enzyme immunoassay. The parents answered questions regarding potential determinants. We found: geometric means (geometric standard deviations) 186 mg/m(2) (4.3) for dust; 5.46 × 10(3) EU/m(2) (8.0) and 31.1 × 10(3) EU/g (2.6) for endotoxin; and 142 μg/m(2) (14.3) and 0.71 × 10(3) μg/g (7.3) for β-(1→3)-D-glucan. High correlations (r > 0.75) were found between floor dust and endotoxin and β-(1→3)-D-glucan loads, while endotoxin and β-(1→3)-D-glucan concentrations were moderately correlated (r = 0.36-0.41) with the dust load. Having a carpet was positively associated with dust load and with endotoxin and β-(1→3)-D-glucan concentrations. Pet keeping, dwelling type, and dwelling location were determinants of endotoxin concentrations. No other determinants were associated with β-(1→3)-D-glucan concentrations. Compared with other European studies, we found lower β-(1→3)-D-glucan loads and concentrations but higher endotoxin loads and concentrations suggesting a geographically determined different composition of Danish floor dust compared with other European regions.

Enhanced Allergic Inflammation of Der p 2 Affected by Polymorphisms of MD-2 Promoter

Purpose

Myeloid differentiation-2 (MD-2) has been associated with endotoxin and inflammatory disorders because it can recognize lipopolysaccharide (LPS) binding and attenuate Toll-like receptor 4 (TLR4)-mediated signaling. However, its role in allergic inflammation has yet to be clarified. We examined whether single nucleotide polymorphisms (SNPs) in MD-2 promoter can affect MD-2 expression and aimed to clarify the relationship between Der p 2 allergy and SNPs of MD-2 promoter.

Methods

The function of SNPs of MD-2 promoter and the effects of cytokines and immunoglobulin on the secretion and mRNA expression were investigated in 73 allergic subjects with different MD-2 gene promoter variants. Peripheral blood mononuclear cells were cultured with or without LPS in the presence of Dermatophagoides pteronyssinus group 2 allergen (Der p 2), followed by mRNA extraction and cytokine expression analysis. The culture supernatants were collected for cytokine measurement.

Results

Patients with the MD-2 promoter SNPs (rs1809441/rs1809442) had increased mRNA expressions of MD-2, ε heavy chain of IgE (Cε), and interleukin (IL)-8; however, only MD-2 and IL-8 were further up-regulated after Der p 2 stimulation. Patients with SNPs of MD-2 promoter tended to have high levels of IL-1β, IL-6, IL-8, IL-10, and tumor necrosis factor (TNF)-α after Der p 2 and LPS stimulation. Increased secretions of IL-6, IL-8, and IL-10 were found to be up-regulated by Der p 2 stimulation, and an increased secretion of IFN-γ and decreased secretion of IL-4 were noted after LPS stimulation.

Conclusions

The high levels of proinflammatory cytokines secreted by Der p 2 were predetermined by MD-2 promoter SNPs (rs1809441/rs1809442). Through cytokine secretion by Der p 2 and LPS, these SNPs may serve as an indicator of the pathological phenotype of Der p 2-induced allergic inflammation.

Childhood asthma: recent developments and update

PURPOSE OF REVIEW

The purpose of this review is to provide an update on childhood asthma specifically related to the underlying genetic background and pathophysiology of asthma and their interaction with environmental stimuli. We will also discuss emerging data in the field of disease phenotyping.

RECENT FINDINGS

The field of genetics is continuously evolving to expand our knowledge on the cause of disease. Childhood onset asthma has been related to atopy and exposure to early-life infections. More recently, phenotypes have been used to classify asthma as transient and persistent, but the association of each phenotype with the genetic origin of asthma is not clearly understood.

SUMMARY

This review covers the topics of genetics, epigenetics, pathophysiology, phenotypes and treatment as they relate to childhood asthma. Overall, it provides a basis for the future of asthma treatment through description of the current research.

Quantity and diversity of environmental microbial exposure and development of asthma: a birth cohort study

Background

Early-life exposure to environmental microbial agents may be associated with the development of allergies. The aim of the study was to identify better ways to characterize microbial exposure as a predictor of respiratory symptoms and allergies.

Methods

A birth cohort of 410 children was followed up until 6 years of age. Bacterial endotoxin, 3-hydroxy fatty acids, N-acetyl-muramic acid, fungal extracellular polysaccharides (EPS) from Penicillium and Aspergillus spp., β-D-glucan, ergosterol, and bacterial or fungal quantitative polymerase chain reactions (qPCRs) were analyzed from dust samples collected at 2 months of age. Asthma, wheezing, cough, and atopic dermatitis were assessed using repeated questionnaires. Specific IgEs were determined at the age of 1 and 6 years.

Results

Only few associations were found between single microbial markers and the studied outcomes. In contrast, a score for the total quantity of microbial exposure, that is, sum of indicators for fungi (ergosterol), Gram-positive (muramic acid) bacteria, and Gram-negative (endotoxin) bacteria, was significantly (inverted-U shape) associated with asthma incidence (P < 0.001): the highest risk was found at medium levels (adjusted odds ratio (aOR) 2.24, 95% confidence interval (95% CI) 0.87–5.75 for 3rd quintile) and the lowest risk at the highest level (aOR 0.34, 95% CI 0.09–1.36 for 5th quintile). The microbial diversity score, that is, sum of detected qPCRs, was inversely associated with risk of wheezing and was significantly (inverted-U shape) associated with sensitization to inhalant allergens.

Conclusion

Score for quantity of microbial exposure predicted asthma better than single microbial markers independently of microbial diversity and amount of dust. Better indicators of total quantity and diversity of microbial exposure are needed in studies on the development of asthma.

Improved exposure characterization with robotic (PIPER) sampling and association with children's respiratory symptoms, asthma and eczema

Particulate matter (PM) and its constituents are recognized risk factors for the development of respiratory symptoms and illness in children. Most measurements of exposure have relied upon stationary indoor monitors (SIMs), overlooking the role of resuspended PM. To improve exposure characterization to resuspended aerosol PM, a recently developed methodology has been employed. The goal of this study was to characterize the resuspendable fraction of house dust and early childhood exposures to PM and its constituents in the child's home and compare conventional SIM and the Pre-toddler Inhalable Particulate Environmental Robotic (PIPER), an innovative mobile sampler. The study seeks to demonstrate that PIPER provides a more relevant estimate of exposure from inhalable particulate matter through improved correlation with respiratory symptoms in young children. Seventy-five households with children between 3 and 59 months of age were recruited from clinics in central New Jersey. Demographic information, and responses to a health questionnaire based upon that used by the International Study of Allergies and Asthma in Childhood (ISAAC), and household data were collected. Household exposures to inhalable PM (PM100) and endotoxin were determined with simultaneous SIM and mobile (PIPER) sampling. Univariate and multivariate analyses were carried out. History of wheeze ("recent" (<1 year) and "ever"), cough, asthma and eczema was evaluated. Multivariate analysis models included PM100 and endotoxin levels by tertiles of exposure. Risk of asthma for the highest tertile of PM100, as measured by PIPER (odds ratio=4.2; 95% confidence interval 0.7-24.0), was compared with measurements by SIM (odds ratio=0.7; 95% confidence interval 0.2-2.6). Measurements of PM and its constituents with PIPER are more strongly associated with asthma, eczema and wheeze compared with measurements using SIMs. Application of this methodology may provide useful insights into early childhood exposures related to the etiology of childhood illnesses associated with inhalation exposures.

Exposure to Beta-(1,3)-D-glucan in house dust at age 7-10 is associated with airway hyperresponsiveness and atopic asthma by age 11-14

BACKGROUND

Mould exposure has been linked to childhood asthma and bronchial hyper-responsiveness. Few studies have assessed beta-(1,3)-d-glucan (beta-glucan), a significant fungal cell wall constituent, in relation to asthma in adolescence.

OBJECTIVE

To determine whether house dust-derived beta-glucan exposure at age 7-10 is associated with the development and persistence of atopic and non-atopic asthma, and bronchial hyper-responsiveness (BHR) by age 11-14.

METHODS

Dust samples were collected from the 1995 Study of Asthma, Genes, and Environment (SAGE) birth cohort. This cohort was derived from Manitoba provincial healthcare administrative records of children high and low risk for asthma. Samples were collected from the homes of 422 children at age 7-10 and analyzed using beta-glucan and endotoxin-specific Limulus Amoebocyte Lysate assays. Asthma, atopy, and BHR status of each child were also assessed at ages 7-10 and 11-14.

RESULTS

At age 7-10, beta-glucan dust levels in the home were associated with persistent atopic asthma at age 11-14 (OR 1.79 for each unit increase in levels, 95% CI 1.14-2.81), independent of endotoxin exposure, and Alternaria or Cladosporium sensitization. The likelihood of BHR almost doubled with unit increases in dust beta-glucan in asthmatic children. In children without asthma, exposure to high beta-glucan levels at age 7-10 also elevated risk for BHR in adolescence (OR 1.74, 95% CI 1.05-2.89). New-onset atopic asthma was twice more likely following high beta-glucan exposure in children without asthma but the association did not reach statistical significance. No associations were evident with concurrent asthma phenotype at age 7-10 or non-atopic asthma at age 11-14.

CONCLUSION

These findings implicate home beta-glucan exposure at school-age as a risk factor for persistent atopic asthma and new-onset BHR. The higher prevalence of BHR in urban adolescents may be propagated by this home exposure.

Perinatal influences on the development of asthma and atopy in childhood

BACKGROUND

In most children with asthma and atopy, onset of disease occurs early in life, indicating a crucial role of in utero and early childhood environment. However, only a small part of this burden of disease established early in life has been explained.

OBJECTIVE

To examine the effects of early environmental exposures on the development of asthma and atopy within the setting of an affluent urban population.

METHODS

The authors followed 526 German children from birth to 5 years of age. Parental interviews in pregnancy and then yearly assessed the health of the child and environmental characteristics. Endotoxin and allergens in house dust were measured at 3 months. Atopic sensitization was assessed at 1 and 5 years.

RESULTS

In atopic mothers, acute atopic symptoms during pregnancy were associated with increased risk of early atopic dermatitis (adjusted odds ratio [aOR] 1.74, 95% confidence interval [CI] 1.00-3.02) and allergic rhinitis at 5 years (aOR 2.11, 95% CI 1.01-4.41). Further, maternal illnesses during pregnancy (ie, repeated common colds) increased the risk of asthma at 5 years (aOR 2.31, 95% CI 1.12-4.78). Endotoxin in the child's mattress was inversely associated with atopic sensitization (aOR 0.79, 95% CI 0.64-0.97) and asthma (aOR 0.71, 95% CI 0.55-0.93). A contrasting effect of early endotoxin and mite exposure was observed for mite sensitization: mite exposure increased the risk of mite sensitization at 5 years (aOR 1.30, 95% CI 1.11-1.53), whereas endotoxin exposure was inversely associated with mite sensitization (aOR 0.73, 95% CI 0.57-0.95).

CONCLUSION

Factors affecting the in utero environment, such as maternal atopy and infections, and bacterial exposure in pregnancy or early life may act as immunomodulators enhancing or inhibiting the development of asthma and atopy in childhood.

Asthma and rhinitis in cleaning workers: a systematic review of epidemiological studies

OBJECTIVE

This article presents a systematic review of epidemiological studies linking cleaning work and risk of asthma and rhinitis.

METHODS

Published reports were identified from PubMed covering the years from 1976 through June 30, 2012. In total, we identified 24 papers for inclusion in the review. The quality of studies was evaluated using the Strengthening of the Reporting of Observational Studies in Epidemiology (STROBE) statement checklist of 22 items for cross-sectional, cohort and case-control studies.

RESULTS

Increased risk of asthma or rhinitis has been shown in 79% of included epidemiological studies. In four studies the increased risk of asthma in cleaning workers was confirmed by objective tests, such as bronchial hyper-reactivity or airflow obstruction. Level of exposure to cleaning products, cleaning sprays, bleach, ammonia, mixing products and specific job tasks has been identified as specific causes of asthma and rhinitis.

CONCLUSIONS

Possible preventive measures encompass the substitution of cleaning sprays, bleach and ammonia, avoidance of mixing products, the use of respiratory protective devices, worker education and medical surveillance.

Exposure to microbial agents in house dust and wheezing, atopic dermatitis and atopic sensitization in early childhood: a birth cohort study in rural areas

BACKGROUND

Early-life exposure to environmental microbial agents may be associated with development of wheezing and allergic diseases.

OBJECTIVE

To assess the association of microbial exposure in rural homes with the risk of asthma, wheezing, atopic dermatitis and sensitization.

METHODS

Birth cohorts of rural children (n = 1133), half from farmer families, were followed up from birth to 2 years of age by questionnaires in five European centres. Endotoxin and extracellular polysaccharides (EPS) of Penicillium and Aspergillus spp. were determined from living room floor and mother's mattress dust samples collected at 2 months of age. Specific IgE against 19 allergens was measured at 1 year of age. Discrete-time hazard models, generalized estimations equations (GEE) and logistic regression were used for statistical analyses.

RESULTS

The incidence of asthma was inversely associated with the amount of dust (adjusted odds ratio (aOR) 0.73, 95% CI 0.58-0.93) and the loads (units/m(2)) of EPS (aOR 0.75, 95% CI 0.55-1.04) and endotoxin (aOR 0.79, 95% CI 0.60-1.05) in the mother's mattress. Similar associations were seen with wheezing and with living room floor dust. The microbial markers were highly correlated and their effects could not be clearly separated. The inverse associations were seen especially among non-farmers. The risk of sensitization to inhalant allergens increased with increasing endotoxin exposure from mattress dust. No associations were observed with concentrations (units/g) or with atopic dermatitis.

CONCLUSION AND CLINICAL RELEVANCE

The amount and microbial content of house dust were inversely associated with asthma and wheezing, but due to high correlations between microbial agents and amount of dust, it was not possible to disentangle their individual effects. New ways to better measure and represent exposure to environmental microbes, including indexes of biodiversity, are needed especially among farmers.

The effects of various doses of bacterial lipopolysaccharide on the expression of CD63 and the release of histamine by basophils of atopic and non-atopic patients

OBJECTIVE

We tested the effect of various doses of bacterial lipopolysaccharide (LPS, endotoxin) on the expression of CD63 and the in vitro release of histamine by basophils stimulated with ragweed allergen in patients with or without ragweed and mite allergies.

METHODS

The peripheral blood of 11 patients with ragweed allergy, 10 patients with mite allergy and 14 control patients was incubated with ragweed allergen extract following pretreatment with varying doses of LPS. The expression of CD63 in basophils was measured by flow cytometry, and the release of histamine was determined by ELISA.

RESULTS

In the samples of patients with ragweed allergy that were exposed to specific allergen, only high doses of LPS significantly elevated the expression of CD63 (200 ng/ml; 1,000 EU/ml) and the release of histamine (2,000 ng/ml; 10,000 EU/ml). There was no effect of LPS in any other cases.

CONCLUSIONS

Bacterial LPS (endotoxin) concentrations higher than 200 ng/ml (1,000 EU/ml), which rarely occurs in nature, could only activate the basophils from atopic patients whilst in the presence of the specific allergen. Thus, the restoration of the urban, "microbe-poor" milieu with endotoxin (as LPS) can be a promising and harmless approach for allergy prevention.

Effect of endotoxin and allergens on neonatal lung function and infancy respiratory symptoms and eczema

BACKGROUND

Exposure to endotoxin and allergens in house dust has been found to be associated with childhood wheeze and asthma. Neonatal lung function is rarely examined in relation to this exposure.

OBJECTIVES

To assess the association between exposure to endotoxin, house dust mite and cat allergens and neonatal lung function, and respiratory symptoms and eczema in infancy.

METHODS

In the Wheezing Illnesses Study Leidsche Rijn (WHISTLER) birth cohort study, levels of endotoxin, house dust mite allergens, and cat allergen have been measured in dust samples collected in the child's home. Lung function was measured before age 2 months, and respiratory symptoms and eczema were recorded in a daily diary during the first year of life. Associations of lung function (N = 302), respiratory symptoms (N = 361), and eczema (N = 342) with endotoxin and allergen levels have been studied by means of linear and logistic regression, respectively.

RESULTS

Mattress dust endotoxin was associated with a significant increase in neonatal respiratory compliance [adjusted mean difference (95% confidence interval) 2.31 (0.33; 4.29) ml/kPa per interquartile range increase in exposure] and a non-significant decrease in neonatal airway resistance [0.32 (-0.77; 0.14) kPa/l/s]. There were no associations between allergen exposure and neonatal lung function and respiratory symptoms.

CONCLUSIONS

Environmental exposure to endotoxin may have an important role in the development of lung function.

The effect of environmental oxidative stress on airway inflammation

PURPOSE OF REVIEW

Asthma is an inflammatory respiratory condition with significantly associated morbidity and mortality that is increasing in prevalence. Air pollution is an important factor in both the development of asthma and in asthma exacerbations. Oxidative stress as a result of exposure to air pollution and underlying genetic polymorphisms that may play a role in susceptibility to this oxidative stress are the subject of current investigation. This article reviews the data regarding the effects of air pollution on the innate immune response and potential clinical and treatment implications of how genetic polymorphisms affect this response.

RECENT FINDINGS

Recent investigation reveals how pollutant-induced oxidative stress impacts airway inflammatory responses. Work by our study group demonstrates that asthmatic patients have an exaggerated inflammatory response to air pollution-induced oxidative stress. New trials investigating antioxidants as potential therapeutic interventions may target this specific issue.

SUMMARY

Air pollution plays a critical role in asthma and may affect certain patients more than others. Further investigation into the genetic polymorphisms that affect inflammatory responses may help target patient populations at greatest risk for air pollution-induced asthma and may provide new therapeutic options for these patient populations.

The association between leisure-time physical activities and asthma symptoms among 10- to 12-year-old children: the effect of living environment in the PANACEA study

OBJECTIVE

This study evaluated the interrelationships of living environment, physical activity, lifestyle/dietary habits, and nutritional status on the prevalence of childhood asthma.

METHODS

In a cross-sectional survey 1125 children (529 boys), 10 to 12 years old, were selected from 18 schools located in an urban environment (Athens, n = 700) and from 10 schools located in rural areas (n = 425) in Greece.

RESULTS

Children living in Athens had higher likelihood of "ever had" asthma compared with children living in rural areas (odds ratio (OR) = 1.78, 95% confidence interval (CI) = 1.25-2.54), after adjusting for age and sex. After adjusting for age, sex, body mass index, and adherence to the Mediterranean diet (KIDMED score), leisure-time physical activity was inversely associated with "ever had" asthma. When stratifying by county of residence, a trend toward reduced asthma symptoms among children engaged in outdoor physical activities during their leisure time who reside in rural (but not urban) environment was observed (OR = 0.88, 95% CI = 0.77-1.01).

CONCLUSIONS

The inverse relationship between asthma symptoms and leisure-time physical activity in the rural environment and the lack of an association between asthma symptoms and organized sports-related activities should draw the attention of public healthcare authorities. Their efforts should focus on the planning of a sustainable natural environment, which will promote the physical health of children and reduce the burden of childhood asthma.