The hygiene hypothesis in allergy and asthma: an update

A systematic review on the development of asthma and allergic diseases in relation to international immigration: the leading role of the environment confirmed

BACKGROUND

The prevalence of asthma and allergic diseases is rising worldwide. Evidence on potential causal pathways of asthma and allergies is growing, but findings have been contradictory, particularly on the interplay between allergic diseases and understudied social determinants of health like migration status. This review aimed at providing evidence for the association between migration status and asthma and allergies, and to explore the mechanisms between migration status and the development of asthma and allergies.

METHODS AND FINDINGS

Systematic review on asthma and allergies and immigration status in accordance with the guidelines set by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The pooled odds ratio (OR) of the prevalence of asthma in immigrants compared to the host population was 0.60 (95% CI 0.45-0.84), and the pooled OR for allergies was 1.01 (95% CI 0.62-1.69). The pooled OR for the prevalence of asthma in first generation versus second generation immigrants was 0.37 (95% CI 0.25-0.58). Comparisons between populations in their countries of origin and those that emigrated vary depending on their level of development; more developed countries show higher rates of asthma and allergies.

CONCLUSIONS

Our findings suggest a strong influence of the environment on the development of asthma and allergic diseases throughout the life course. The prevalence of asthma is generally higher in second generation than first generation immigrants. With length of residence in the host country the prevalence of asthma and allergic diseases increases steadily. These findings are consistent across study populations, host countries, and children as well as adults. Differences have been found to be significant when tested in a linear model, as well as when comparing between early and later age of migration, and between shorter and longer time of residence.

Influence of farming exposure on the development of asthma and asthma-like symptoms

Based upon age and type of farming exposures, a wide range of studies demonstrate either protective or deleterious effects of the farming environment on asthma. In this review, we highlight key studies supporting the concept that farming exposure protects children from asthma and atopy based on studies performed largely in European pediatric cohorts. Various types of farming in certain regions appear to have a greater effect on asthma protection, as does the consumption of unpasteurized milk. In the United State, where concentrated animal feeding operations (CAFOs) are more common, asthma is increased in children exposed especially to swine CAFOs; whereas, rates of atopy and allergy are lower in these children. We also review studies evaluating the role of farming exposures both as a child and/or as an adult on asthma seen in adults. The importance of microbes in farming environments and the contribution of various components of the innate immune system including toll-like receptors to the underlying mechanisms of asthma related to farming exposures are also reviewed.

Immunotherapy of type-1 allergies with virus-like particles and CpG-motifs

Immunotherapy of type-I-allergies is regarded as the most efficient treatment option besides allergen avoidance. Different forms of allergen preparations are used as well as different routes of application. Virus-like particles represent a potent vaccine platform with proven immunogenicity and clinical efficacy. The addition of toll-like receptor ligands and/or depot-forming adjuvants further enhances immune cell activation. This article will focus on the function of virus-like particles loaded with DNA rich in CpG-motifs and discuss clinical experience in treatment of allergic rhinitis. Evidence will be presented that clinically effective treatment can be obtained even in the absence of allergens. Results encourage further investigation of virus-like particles and CpG-motifs in immunotherapy, either as a stand alone product, or as adjuvants for allergen-specific immunotherapy.

Examining mediators of housing mobility on adolescent asthma: results from a housing voucher experiment

Literature on neighborhood effects on health largely employs non-experimental study designs and does not typically test specific neighborhood mediators that influence health. We address these gaps using the Moving to Opportunity (MTO) housing voucher experiment. Research has documented both beneficial and adverse effects on health in MTO, but mediating mechanisms have not been tested explicitly. We tested mediation of MTO effects on youth asthma (n = 2829). MTO randomized families living in public housing to an experimental group receiving a voucher to subsidize rental housing, or a control group receiving no voucher, and measured outcomes 4-7 years following randomization. MTO had a harmful main effect vs. controls for self-reported asthma diagnosis (b = 0.24, p = 0.06), past-year asthma attack (b = 0.44, p = 0.02), and past-year wheezing (b = 0.17, p = 0.17). Using Inverse Odds Weighting mediation we tested mental health, smoking, and four housing dimensions as potential mediators of the MTO-asthma relationship. We found no significant mediation overall, but mediation may be gender-specific. Gender-stratified models displayed countervailing mediation effects among girls for asthma diagnosis by smoking (p = 0.05) and adult-reported housing quality (p = 0.06), which reduced total effects by 35% and 42% respectively. MTO treatment worsened boys' mental health and mental health reduced treatment effects on asthma diagnosis by 27%. Future research should explore other potential mediators and gender-specific mediators of MTO effects on asthma. Improving measurement of housing conditions and other potential mediators may help elucidate the "black box" of neighborhood effects.

Broncho-Vaxom attenuates allergic airway inflammation by restoring GSK3β-related T regulatory cell insufficiency

Background

Oral administration of bacterial extracts (eg, Broncho-Vaxom (BV)) has been proposed to attenuate asthma through modulating Treg cells. However, the underlying mechanism has not been fully characterized. This study sought to assess the effects of oral administration of BV on GSK-3β expression and Treg cells in ovalbumin (OVA)-induced asthmatic mice models.

Method

Asthmatic mice models were established with OVA challenge and treated with oral administration of BV. Next, infiltration of inflammatory cells including eosinophil and neutrophils, mucous metaplasia, levels of Th1/Th2/Treg-typed cytokines and expression of GSK3β and Foxp3 were examined in asthmatic mice models by histological analysis, Bio-Plex and western blot, respectively. Moreover, the frequencies of Treg cells were evaluated in cultured splenocytes by flow cytometry in the presence of BV or GSK3β siRNA interference.

Results

We found significant decrease of infiltrated inflammatory cells in bronchoalveolar lavage fluid (BALF) in asthmatic mice models after oral administration of BV. Oral administration of BV was shown to significantly suppress mucus metaplasia, Th2-typed cytokine levels and GSK3β expression while increasing Foxp3 production in asthmatic mice models. Moreover, BV significantly enhanced GSK3β-related expansion of Treg cells in cultured spleen cells in vitro.

Conclusion

Our findings provide evidence that oral administration of BV is capable of attenuating airway inflammation in asthmatic mice models, which may be associated with GSK3β-related expansion of Treg cells.

Early life events influence whole-of-life metabolic health via gut microflora and gut permeability

The capacity of our gut microbial communities to maintain a stable and balanced state, termed 'resilience', in spite of perturbations is vital to our achieving and maintaining optimal health. A loss of microbial resilience is observed in a number of diseases including obesity, diabetes and metabolic syndrome. There are large gaps in our understanding of why an individual's co-evolved microflora consortium fail to develop resilience thereby establishing a trajectory towards poor metabolic health. This review examines the connections between the developing gut microbiota and intestinal barrier function in the neonate, infant and during the first years of life. We propose that the effects of early life events on the gut microflora and permeability, whilst it is in a dynamic and vulnerable state, are fundamental in shaping the microbial consortia's resilience and that it is the maintenance of resilience that is pivotal for metabolic health throughout life. We review the literature supporting this concept suggesting new potential research directions aimed at developing a greater understanding of the longitudinal effects of the gut microflora on metabolic health and potential interventions to recalibrate the 'at risk' infant gut microflora in the direction of enhanced metabolic health.

Traditional cheeses: rich and diverse microbiota with associated benefits

The risks and benefits of traditional cheeses, mainly raw milk cheeses, are rarely set out objectively, whence the recurrent confused debate over their pros and cons. This review starts by emphasizing the particularities of the microbiota in traditional cheeses. It then describes the sensory, hygiene, and possible health benefits associated with traditional cheeses. The microbial diversity underlying the benefits of raw milk cheese depends on both the milk microbiota and on traditional practices, including inoculation practices. Traditional know-how from farming to cheese processing helps to maintain both the richness of the microbiota in individual cheeses and the diversity between cheeses throughout processing. All in all more than 400 species of lactic acid bacteria, Gram and catalase-positive bacteria, Gram-negative bacteria, yeasts and moulds have been detected in raw milk. This biodiversity decreases in cheese cores, where a small number of lactic acid bacteria species are numerically dominant, but persists on the cheese surfaces, which harbour numerous species of bacteria, yeasts and moulds. Diversity between cheeses is due particularly to wide variations in the dynamics of the same species in different cheeses. Flavour is more intense and rich in raw milk cheeses than in processed ones. This is mainly because an abundant native microbiota can express in raw milk cheeses, which is not the case in cheeses made from pasteurized or microfiltered milk. Compared to commercial strains, indigenous lactic acid bacteria isolated from milk/cheese, and surface bacteria and yeasts isolated from traditional brines, were associated with more complex volatile profiles and higher scores for some sensorial attributes. The ability of traditional cheeses to combat pathogens is related more to native antipathogenic strains or microbial consortia than to natural non-microbial inhibitor(s) from milk. Quite different native microbiota can protect against Listeria monocytogenes in cheeses (in both core and surface) and on the wooden surfaces of traditional equipment. The inhibition seems to be associated with their qualitative and quantitative composition rather than with their degree of diversity. The inhibitory mechanisms are not well elucidated. Both cross-sectional and cohort studies have evidenced a strong association of raw-milk consumption with protection against allergic/atopic diseases; further studies are needed to determine whether such association extends to traditional raw-milk cheese consumption. In the future, the use of meta-omics methods should help to decipher how traditional cheese ecosystems form and function, opening the way to new methods of risk-benefit management from farm to ripened cheese.

Allergens are not pathogens: why immunization against allergy differs from vaccination against infectious diseases

Vaccination against infectious diseases has been one of the major breakthroughs in human medical history, saving the lives of millions of people each year. More recently, prophylactic vaccination against non-infectious diseases such as cancer, Alzheimer’s disease, diabetes, and type I allergy is being investigated. Particularly in case of IgE-driven allergic disorders, which afflict almost a quarter of the population in highly developed countries, preventative measures would represent a major improvement for patients’ health as well as an economic relief for public health services. As an alternative to allergen-specific immunotherapy, prophylactic vaccination against type I allergic diseases could slow down or even stop the progress of the allergy pandemic. Allergen-encoding gene-based vaccines, i.e., plasmid DNA and mRNA vaccines, provide the advantage of purity over crude allergen extracts, which involve the risk of de novo sensitizations. Furthermore, these formulations have been demonstrated to induce T helper 1 as well as T regulatory immune responses—a pre-requisite for prophylactic intervention against allergies. However, prophylactic vaccines against environmental allergens strikingly differ from conventional vaccines against infectious diseases or therapeutic approaches concerning the underlying immunological mechanisms.

The role of the environment in the development of pediatric inflammatory bowel disease

The incidence of inflammatory bowel disease (IBD) is rising worldwide, with a particularly sharp increase in children. Rates are highest in North America and Europe, with rapid increases noted in developing nations adopting the Westernized environment. While many genetic risk loci have been identified that predispose people to IBD, incomplete penetrance and overlapping genotypes among patients with different phenotypes inadequately explain the etiology of these chronic diseases. Therefore, environmental risk factors have been the subject of much recent research. This article reviews the role of the environment in IBD, with particular focus on early-life exposures and pediatric-onset disease. The literature surrounding environmental risk factors is reviewed, including prenatal and perinatal exposures, the hygiene hypothesis, the urban environment, infection and antibiotic use, and secondhand tobacco smoke exposure. In addition, the possible role of the environment in altering the intestinal microbiome is addressed.

Endocrine disruptors found in food contaminants enhance allergic sensitization through an oxidative stress that promotes the development of allergic airway inflammation

In the past few decades, there has been a significant increase in incidence of allergic diseases. The hygiene hypothesis may provide some clues to explain this rising trend, but it may also be attributable to other environmental factors that exert a proallergic adjuvant effects. However, there is limited information on the risks of developing allergic asthma and related diseases through the ingestion of environmental chemicals found in food contaminants. In the present study, we have shown that oral administration of tributyltin, used as a model environmental chemical, induced oxidative-stress status in the bronchial lymph node, mesenteric lymph node and spleen, but not in the lung, where the initial step of allergic asthma pathogenesis takes place. Mice exposed to tributyltin exhibited heightened Th2 immunity to the allergen with more severe airway inflammation. Tributyltin also induced Treg cells apoptosis preferentially over non-Treg cells. All these effects of tributyltin exposure were canceled by the administration of glutathione monoethyl ester. Meanwhile, tributyltin did not affect airway inflammation of mice transferred with allergen-specific Th2 cells. Collectively, these results suggest that tributyltin exerts its pathological effect during the sensitization phase through oxidative stress that enhances the development of allergic diseases. The current study dissects the pathogenic role of oxidative stress induced by oral exposure to an environmental chemical during the sensitization phase of allergic airway inflammation and would be important for developing therapeutics for prevention of allergic diseases.

Severity of allergic airway disease due to house dust mite allergen is not increased after clinical recovery of lung infection with Chlamydia pneumoniae in mice

Chlamydia pneumoniae is associated with chronic inflammatory lung diseases like bronchial asthma and chronic obstructive pulmonary disease. The existence of a causal link between allergic airway disease and C. pneumoniae is controversial. A mouse model was used to address the question of whether preceding C. pneumoniae lung infection and recovery modifies the outcome of experimental allergic asthma after subsequent sensitization with house dust mite (HDM) allergen. After intranasal infection, BALB/c mice suffered from pneumonia characterized by an increased clinical score, reduction of body weight, histopathology, and a bacterial load in the lungs. After 4 weeks, when infection had almost resolved clinically, HDM allergen sensitization was performed for another 4 weeks. Subsequently, mice were subjected to a methacholine hyperresponsiveness test and sacrificed for further analyses. As expected, after 8 weeks, C. pneumoniae-specific antibodies were detectable only in infected mice and the titer was significantly higher in the C. pneumoniae/HDM allergen-treated group than in the C. pneumoniae/NaCl group. Intriguingly, airway hyperresponsiveness and eosinophilia in bronchoalveolar lavage fluid were significantly lower in the C. pneumoniae/HDM allergen-treated group than in the mock/HDM allergen-treated group. We did observe a relationship between experimental asthma and chlamydial infection. Our results demonstrate an influence of sensitization to HDM allergen on the development of a humoral antibacterial response. However, our model demonstrates no increase in the severity of experimental asthma to HDM allergen as a physiological allergen after clinically resolved severe chlamydial lung infection. Our results rather suggest that allergic airway disease and concomitant cellular changes in mice are decreased following C. pneumoniae lung infection in this setting.

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.

Asthma phenotyping, therapy, and prevention: what can we learn from systems biology?

Asthma has a high prevalence worldwide, and contributes significantly to the socioeconomic burden. According to a classical paradigm, asthma symptoms are attributable to an allergic, Th2-driven airway inflammation that causes airway hyperresponsiveness and results in reversible airway obstruction. Diagnosis and therapy are based mainly on these pathophysiologic concepts. However, these have increasingly been challenged by findings of recent studies, and the frequently observed failure in controlling asthma symptoms. Important recent findings are the protective "farm effect" in children, the possible prenatal mechanisms of this protection, the recognition of many different asthma phenotypes in children and adults, and the partly disappointing clinical effects of new targeted therapeutic approaches. Systems biology approaches may lead to a more comprehensive view of asthma pathophysiology and a higher success rate of new therapies. Systems biology integrates clinical and experimental data by means of bioinformatics and mathematical modeling. In general, the "-omics" approach, and the "mathematical modeling" approach can be described. Recently, several consortia have been attempting to bring together clinical and molecular data from large asthma cohorts, using novel experimental setups, biostatistics, bioinformatics, and mathematical modeling. This "systems medicine" approach to asthma will help address the different asthma phenotypes with adequate therapy and possibly preventive strategies.

Increased prevalence of self-reported asthma among Korean adults: an analysis of KNHANES I and IV data

BACKGROUND

Asthma is one of the most common chronic conditions. Knowing the longitudinal trends of prevalence is important in developing health service planning and in assessing the impact of the disease. However, there have been no studies that examined current asthma prevalence trends in Korea through the analysis of nationwide surveys.

METHODS

Data were acquired from patients aged 20-59 years who participated in the First Korean National Health and Nutritional Examination Surveys (KNHANES), which was conducted in 1998, and in the second year of the Fourth KNHANES, which was conducted in 2008. To estimate the prevalence of asthma with age and gender standardization, we used data from the Population and Housing Census, which was conducted by Statistics Korea in 2005.

RESULTS

The prevalence of physician-diagnosed asthma increased from 1998 to 2008 (1998: 0.7 %, 2008: 2.0 %). The prevalence of asthma medication usage also increased from 1998 to 2008 (1998: 0.3 %, 2008: 0.7 %); however, the prevalence of wheezing decreased between 1998 and 2008 (1998: 13.7 %, 2008: 6.3 %). A similar trend was observed after estimating the prevalence of asthma with age and gender standardization. Allergic rhinitis might be the reason for the increased prevalence of physician-diagnosed asthma, while the observed decrease in wheezing may be related to the decrease in smoking or the increase in the use of asthma medication.

CONCLUSIONS

The present study showed that the prevalence of both self-reported physician-diagnosed asthma and asthma medication usage increased from 1998 to 2008 in Korea, despite a possible changing pattern of diagnosing asthma.

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.