Update on environmental determinants of allergic diseases.

Is it all in our genes? The “mite-y” truth

What should we tell allergic families about pets?

Environmental and occupational allergies

Allergic diseases are quite prevalent worldwide, and the incidence of allergy is increasing everywhere [1-7]. Because allergic and immunologic processes overlap all organ systems, allergy is not always taught in medical schools as a separate subject. Indeed, lack of recognition of the specialty and of the need to teach about allergic and immunologic diseases results in allergy not being included at all in some medical school curricula [8]. With an estimated 22% of the global population experiencing allergic and immunologic diseases, it is time to recognize and strengthen education in allergy and immunology [8]. The World Allergy Organization (WAO), an alliance of 74 national and regional allergy societies, created this consensus document to establish educational guidelines for worldwide application to help identify and correct allergy education and training deficiencies and to define appropriate competencies. In creating this consensus, it is recognized that each country has its own principles and goals in medical education at the undergraduate and postgraduate levels. This document defines what WAO considers medical practitioners should know to care appropriately for allergic patients.

Gene-environment interaction in allergic disease: More questions, more answers?

A close relationship has been described between atopy, allergic rhinitis and asthma. The purpose of this work was to review recent data that have become available on the interactions between these conditions and the ways in which they influence one another. Recent findings support previous observations suggesting that atopic dermatitis and rhinitis often accompany or precede the development of asthma. Further data support the notion that early-life exposure to domestic animals, a farming environment, passive smoking, and being raised in a large family, may be protective against the development of atopy and/or allergic diseases, although this seems modulated by genetic factors. Furthermore, the appearance of house-dust-mite-specific immunoglobulin E antibodies in early childhood has been identified as a major risk factor for the development of asthma in children with atopic dermatitis; and the association between sensitization to specific allergens and airway hyperresponsiveness was reported to be the strongest for indoor allergens such as house-dust-mite and cat. Allergen exposure can increase airway responsiveness in non-asthmatic subjects with allergic rhinitis and is associated with an increase in markers of lower airway inflammation, particularly with indoor allergens. Furthermore, nasal allergen provocation can induce bronchial inflammation and vice versa, suggesting close interrelations between upper and lower airways. In summary, the recent observations on the relationships between atopy, rhinitis and asthma support the hypothesis of a unique systemic condition with variable manifestations, which may develop following an imbalance between T helper cell types 1 and 2 lymphocyte populations. The latter may be influenced by environmental exposure in early life. Upper- and lower-airway inflammatory events influence each other, supporting the concept of 'united airways'. Further studies should look at the relationships between these conditions to identify individuals at high-risk of developing them and develop strategies to possibly prevent their onset.

The Editors' Choice

Allergic diseases are one of the most common and important diseases that can exert hazardous effects on children's health. The prevalence of allergic diseases in childhood is gradually increasing all over the world in recent decades. Known causes of these diseases include anomalous immune responses and allergic inflammatory reactions, but the causes of allergic diseases in childhood are complex. PubMed, Cochrane Library, Embase and Web of Science were searched for articles focusing on environmental exposure during pregnancy and the risk of childhood allergic diseases, including asthma and atopic dermatitis, and the possible underlying mechanism. In terms of environmental factors, allergic diseases in childhood are closely related to environmental chemical exposure during pregnancy, including bisphenols, phthalates acid esters, perfluorochemicals, polybrominated diphenyl ethers, and polychlorinated biphenyls. However, allergic diseases in childhood are also closely associated with maternal dietary nutrition, maternal intake of drugs, such as acetylsalicylic acid (aspirin), paracetamol and antibiotics, and maternal lifestyle. Several harmful environmental factors during pregnancy can result in the interruption of the function of helper T cells (Th1/Th2), cytokines and immunoglobulins and may activate allergic reactions, which can lead to allergic diseases during childhood.

Exposome study for allergic diseases in children: Rationale and design of ECHO-COCOA study.

Atopic dermatitis(AD)is a chronic, recurrent, inflammatory skin disease in children. The disease is characterized by dryness, chronic eczema-like lesions and obvious itching, seriously affecting the quality of life of children and their families. The pathogenesis of AD is not yet to be clear, and it might be the interaction of genetic susceptibility and environmental exposure to induce skin barrier impairment and immune system dysfunction. In recent years, the role of maternal factors or intrauterine environment exposure on childhood allergic diseases has been attracted attention, and the hypothesis that allergic diseases originate from the fetal period has been postulated. Maternal exposures called "early life exposure", such as nutritional factors during pregnancy (folate, vitamin D, vitamin E and polyunsaturated fatty acid) and tobacco exposure, home environmental exposure may be related with childhood atopic dermatitis. This article would focus on the recent research about maternal nutritional factors and family environmental exposure during pregnancy on offspring's atopic dermatitis.

Environmental exposure is a growing public health burden associated with several negative health effects. An estimated 4.2 million deaths occur each year from ambient air pollution alone. Biomarkers that reflect specific exposures have the potential to measure the real integrated internal dose from all routes of complex environmental exposure. MicroRNAs (miRNAs), small non-coding RNAs that regulate gene expression, have been studied as biomarkers in various diseases and have also shown potential as environmental exposure biomarkers. Here, we review the available human epidemiological and experimental evidence of miRNA expression changes in response to specific environmental exposures including airborne particulate matter. In doing so, we establish that miRNA exposure biomarker development remains in its infancy and future studies will need to carefully consider biological and analytical ‘design rules’ in order to facilitate clinical translation.

Understanding the mechanisms involved in the development of asthma and allergic diseases is expanding, due in part to sequencing advances that have led to the identification of new viral strains such as human rhinovirus strain C (HRV-C) and the human microbiome project. Recent studies have identified new ways in which viral and microbial exposures in early life interact with host genetic background/variants to modify the risk for developing asthma and allergic diseases. Recent research suggests that HRV-C is the main pathogenic agent associated with infant wheeze, hospitalizations and likely the subsequent development of asthma. Pulmonary He MRI suggests that HRV infection in early childhood and subsequent immune responses initiate airway remodeling. Numerous studies of the microbiome indicate that intestinal and airway microbiome diversity and composition contribute to the cause of asthma and allergic diseases. Susceptibility to asthma and allergic diseases is complex and involves genetic variants and environmental exposures (bacteria, viruses, smoking, and pet ownership), alteration of our microbiome and potentially large-scale manipulation of the environment over the past century.

Directing the innate immune response to prevent and control allergic diseases

Allergy and infection have being exerted seriously adverse effect on children’s health. On the one hand, asthma and allergy have become the most common chronic diseases in childhood and the leading cause of pediatric hospitalization worldwide. The prevalence of childhood asthma has considerably increased since the 1950s, with some suggestion of plateauing in developed regions but rapidly increasing in low- and middle-income countries over recent years. On the other hand, pneumonia as the most prevalent infectious disease is the leading cause of mortality in children under 5 years old globally. Approximately 99% of the pneumonia death occurs in developing countries. During recent decade, China has witnessed a rapid increase in the prevalence of childhood asthma and allergies and the morbidity of childhood infectious diseases such as pneumonia tend to be very high. Environmental exposure is thought to be the most important factor which is responsible for this rising trend and serious burden of childhood allergic and infectious diseases. Ambient air pollution has been widely suggested to be associated with the incidence and prevalence of allergies and infections, and a distinct need is then to find out the key component of air pollution and the critical exposure window so as to develop more effective measures of prevention and intervention. A large body of evidence mainly from developed countries suggested that traffic-related air pollution (TRAP) plays a key role in the exacerbation and development of allergies and infections. However, differences in the chemical and physical composition of air pollution, both in level and source, between China and developed countries prompts the need for further investigation into the role of outdoor air pollution in the development of childhood allergic and infectious diseases. On the other hand, due to the rapid urbanization progress in China, a huge number of people, especially the new couples and expected parents, migrated into new buildings in urban areas during the past decade. New building materials, decoration materials, and new furniture caused high indoor level chemicals, such as volatile and semi volatile organ compounds (VOCs and SVOCs). Due to lack of central air conditioning and heating systems, mold and dampness in dwellings is very serious in the southern China with subtropical climate. Thus, indoor environmental risk factors are also serious in China, which play important role in the rapid increase in the allergic diseases and high prevalence of infectious diseases in childhood. Although the impact of environmental pollution on children’s health has attracted wide attention and extensive research, some key scientific issues such as “main environmental pollutants, critical exposure windows, and whether the exposure cause diseases” still remain unclear. This paper summarizes the effects of prenatal (one year before pregnancy, entire pregnancy and three trimesters of pregnancy) and postnatal (first year, past year, and entire postnatal period) exposure to both indoor and outdoor environmental pollution on childhood allergic and infectious diseases, and also analyzed the relative importance of the critical exposure time windows for different diseases. We concluded that most studies mainly from developed countries found a positive association between traffic related air pollution and childhood allergic diseases. However, in China, early life exposure to classical air pollution (such as industrial air pollution) also exerts an adverse effect on childhood asthma and allergies. The recent studies identified relative importance of traffic-related air pollution exposure in different critical time windows (such as different trimester of pregnancy) in the development of different allergic diseases. This paper also concluded that early-life exposure to indoor mould/dampness and renovation significantly increased risk of childhood allergic and infectious diseases. According to the analysis of available literatures, this study proved the hypothesis of “fetal origins of disease” in children, and revealed that exposure to indoor and outdoor environmental pollution during pregnancy and early postnatal period played an important role in the onset and development of childhood allergic and infectious diseases, which provides a scientific basis for effective prevention and intervention strategies to reduce childhood allergies and infections. Finally, this study summarized the different influences, and expected the problems and challenges of effective prevention and reduction of childhood allergies and infections.

Studies in comparison with allergic diseases and sensitization between rural and urban environments in westernized countries might be biased and not adequately reflect countries undergoing rapid transition. A total of 5542 schoolchildren from urban area and 5139 from rural area were recruited for the EuroPrevall-INCO survey. A subsequent case-control sample with 196 children from urban area and 202 from rural area was recruited for a detailed face-to-face questionnaire and assessment of sensitization. Skin prick tests and serum-specific IgE measurements were used to assess sensitizations against food and aeroallergens. Logistic regression analysis was used to determine associations between risk/protective factors, food adverse reactions (FAR), allergic diseases, and sensitizations. Prevalence of self-reported allergic diseases, including asthma (6.6% vs.2.5%), rhinitis (23.2% vs.5.3%), and eczema (34.1% vs.25.9%), was higher in urban than in rural children. Urban children had a significantly higher prevalence of FAR and related allergic diseases, and lower food/inhalation allergen sensitization rate, than those of rural children. In urban children, frequent changing places of residency (odds ratio 2.85, 95% confidence interval: 1.45-5.81) and antibiotic usage (3.54, 1.77-7.32) in early life were risk factors for sensitization, while sensitization and family history of allergy were risk factors for allergic diseases. In rural children, exposure to rural environments in early life was protective against both allergen sensitizations (0.46, 0.21-0.96) and allergic diseases (0.03, 0.002-0.19). We observed a disparity in rates of allergic diseases and allergen sensitization between rural and urban children. In addition to family history, the development of allergic diseases and allergen sensitization were associated with specific urban/rural environmental exposures in early life.