Identification of fungal candidates for asthma protection in a large population-based study

Cattle farm dust alters cytokine levels in human airway construct model

Epidemiological studies have revealed some alterations in systemic immunity that associate with farm exposure and the risk of respiratory diseases, but in vitro studies focusing on immunological responses in the airways are scarce. Our aim was to assess how cowshed dust affects the integrity and inflammation of human airway tissue in vitro. Cowshed dust samples were collected from four different dairy farms. Lung tissue constructs were exposed to dust samples in air-liquid interface. Transepithelial resistance of the tissue, secreted proteins, and a panel of pro-inflammatory cytokines, growth factors, and chemokines were analysed. Cowshed dust stimulation was associated mainly with increased production of IL-13, IL-15, IP-10 and IFN-γ. Some differences between farms were seen. Only one farm dust sample induced a significant change in transepithelial resistance, whereas dust from two of the farms induced the secretion of proteins. The exposure to cowshed dust affected protein and cytokine secretion, but the response profiles were not uniform between farms. The effect on tight junction dynamics was less pronounced, suggesting the relevance of soluble factors in induced responses in the airways. Our results indicate that in addition to farm type, the contribution of cowshed characteristics to dust composition and its immunomodulatory properties should be taken into account.

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 Impact of Ambient Environmental Exposures to Microbial Products on Asthma Outcomes from Birth to Childhood

Purpose of Review

Asthma is a chronic respiratory condition with increasing domestic and worldwide prevalence that burdens individuals and the healthcare system with high costs associated with long-term treatments and acute emergency room (ER) visits. It can be triggered by ambient microbes, including bacteria, viruses, and fungi. In this review, we examine the outcomes of asthma patients in relation to environmental exposures to ambient microbe products, focusing on whether exposure leads to asthma development from birth to childhood and if particular microbes are associated with worsened asthma exacerbations.

Recent Findings

Bacterial endotoxin is more prominent in homes with pets and may cause cytokine cascades that lead to asthma exacerbation. However, some studies have demonstrated a protective effect with early exposure. Patients with positive Aspergillus skin testing are more prone to moderate-severe or severe-uncontrolled asthma. Fungal sensitization is also associated with earlier onset of asthma and demonstrates a dose-dependent relationship of symptom severity and duration. Among viruses, rhinovirus has the greatest association with decreased lung function, severe asthma, and asthma-related hospital admissions. Distribution of microbial products and associated asthma symptoms depends on the geographical climate. Genetic variations among individuals also mitigate the effects of microbial products on asthma development and symptom severity.

Summary

Microbial products of bacteria, fungi, and viruses are associated with the development of asthma, more severe asthma symptoms, and worse outcomes. However, some early exposure studies have also demonstrated a protective effect. Bacterial and fungal products are related to decreased lung function and earlier onset of asthma. Viral products are related to asthma-associated hospital admissions; and the climate and patient genetics can also temper or intensify the relationships between microbial products, asthma development, and asthma symptom severity. Further research should focus on the effects of early microbe exposure and its interaction with human immune systems and asthma-related outcomes.

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.

Indoor bacteria and asthma in adults: a multicentre case-control study within ECRHS II

Both protective and adverse effects of indoor microbial exposure on asthma have been reported, but mostly in children. To date, no study in adults has used non-targeted methods for detection of indoor bacteria followed by quantitative confirmation.A cross-sectional study of 198 asthmatic and 199 controls was conducted within the European Community Respiratory Health Survey (ECRHS) II. DNA was extracted from mattress dust for bacterial analysis using denaturing gradient gel electrophoresis (DGGE). Selected bands were sequenced and associations with asthma confirmed with four quantitative PCR (qPCR) assays.15 out of 37 bands detected with DGGE, which had at least a suggestive association (p<0.25) with asthma, were sequenced. Of the four targeted qPCRs, Clostridium cluster XI confirmed the protective association with asthma. The association was dose dependent (aOR 0.43 (95% CI 0.22-0.84) for the fourth versus first quartile, p for trend 0.009) and independent of other microbial markers. Few significant associations were observed for the three other qPCRs used.In this large international study, the level of Clostridium cluster XI was independently associated with a lower risk of prevalent asthma. Results suggest the importance of environmental bacteria also in adult asthma, but need to be confirmed in future studies.