The association between endotoxin in house dust with atopy and exercise-induced bronchospasm in children with asthma

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.

Effectiveness of portable HEPA air cleaners on reducing indoor endotoxin, PM10, and coarse particulate matter in an agricultural cohort of children with asthma: A randomized intervention trial

We conducted a randomized trial of portable HEPA air cleaners in the homes of children age 6-12 years with asthma in the Yakima Valley, Washington. All families received asthma education while intervention families also received two HEPA cleaners (child's bedroom, living room). We collected 14-day integrated samples of endotoxin in settled dust and PM₁₀ and PM_10-2.5 in the air of the children's bedrooms at baseline and one-year follow-up, and used linear regression to compare follow-up levels, adjusting for baseline. Seventy-one families (36 HEPA, 35 control) completed the study. Baseline geometric mean (GSD) endotoxin loadings were 1565 (6.3) EU/m² and 2110 (4.9) EU/m² , respectively, in HEPA vs. control homes while PM₁₀ and PM_10-2.5 were 22.5 (1.9) μg/m³ and 9.5 (2.9) μg/m³ , respectively, in HEPA homes, and 19.8 (1.8) μg/m³ and 7.7 (2.0) μg/m³ , respectively, in control homes. At follow-up, HEPA families had 46% lower (95% CI, 31%-57%) PM₁₀ on average than control families, consistent with prior studies. In the best-fit heterogeneous slopes model, HEPA families had 49% (95% CI, 6%-110%) and 89% lower (95% CI, 28%-177%) PM_10-2.5 at follow-up, respectively, at 50th and 75th percentile baseline concentrations. Endotoxin loadings did not differ significantly at follow-up (4% lower, HEPA homes; 95% CI, -87% to 50%).

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.

Asthma prevalence, but not allergic rhinitis nor atopic dermatitis, is associated to exposure to dogs in adolescents

BACKGROUND

Exposure to pets can be a predisposing factor in the development of certain diseases, including allergic diseases.

OBJECTIVE

We analyzed the role that exposure to indoor dogs and cats plays in the prevalence of allergic diseases.

METHODS

We examined the cross-sectional data of 1056 women and 936 men aged 15 to 18 years; these individuals were selected through stratified and cluster random sampling. We asked all participants about their exposure to indoor dogs and cats during the year that preceded our study. The prevalence of allergic diseases was determined through core questions taken from The International Study of Asthma and Allergies in Childhood questionnaire.

RESULTS

The prevalence was 12.7% (95% CI: 11.3%-14.2%) for asthma, 9.0% (95% CI: 7.8%-10.4%) for allergic rhinitis, and 5.2% (95% CI: 4.3%-6.2%) for atopic dermatitis. The multivariate analyses showed that exposure to indoor dogs, but not indoor cats, was associated with asthma prevalence (aOR 1.37; 95% CI: 1.03-1.83), as was male sex (aOR=1.42; 95% CI: 1.08-1.86), a personal history of allergic rhinitis (aOR=3.24; 95% CI: 2.25-4.66), and a maternal history of asthma (aOR=3.06; 95% CI: 1.89-4.98). The population attributable risk for exposure to indoor dogs was 18%. Notably, neither allergic rhinitis nor atopic dermatitis was found to be associated with dog or cat exposure (p> 0.05).

CONCLUSION

Exposure to dogs in late adolescence is a factor associated with asthma, although its contribution to the development of asthma should be investigated in new studies.

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.