Features of the bronchial bacterial microbiome associated with atopy, asthma and responsiveness to inhaled corticosteroid treatment

It’s been known that asthmatic lungs are different from healthy lungs in many aspects, including housing different strains of bacteria.  So far, studies haven’t been able to tell whether these differences are due to asthma, associated allergies (atopy), or treatment with different drugs.  They also haven’t been able to determine how these differences affect the way asthma manifests itself and how asthma can be treated.  In this month’s issue of JACI, Durack and colleagues aim to answer these pressing questions (J Allergy Clin Immunol 2017; 140(1): 63-75).

Durack and other investigators looked at the bacterial communities in 84 individuals, split into three groups: (1) 42 atopic asthmatic subjects, (2) 21 atopic non-asthmatic subjects, and (3) 21 non-atopic non-asthmatic, otherwise healthy, subjects.  They also looked at inflammatory markers and changes in bronchial hyperresponsiveness after 6 weeks of treatment with fluticasone, an inhaled steroid commonly used for asthma treatment.

What they found is that the types of bacteria in each of the three groups were significantly different. This included the group with atopy without asthma, suggesting that atopy itself is associated with different patterns of bacterial colonization of the bronchi, but these patterns also differed from those in the subjects with atopic asthma.  The bacteria seen in the asthmatic patients expressed genes for different metabolic pathways that result in products previously linked to risks for asthma development.  And subjects with high levels of allergy/atopy-related inflammation markers in their bronchial epithelium (“T2-high asthma”) had overall lower amounts of bacteria.  Differences were also found in the asthmatic subjects who responded to fluticasone, in that their bronchial bacteria were less different from those in healthy subjects than were the bronchial bacteria in the non-responsive asthmatics.  

Overall these findings suggest that bacterial composition in the lungs is associated with various immunologic and clinical features of the disease.  It also suggests that targeting these bacteria may be a way to help prevent, or even treat, asthma in the future.

Early-life Farm Exposures and Adult Asthma and Atopy in the Agricultural Lung Health Study

Allergies and asthma are growing public health problems, as rates have continued to increase over the past 50 years.  In that same time period, there has been a dramatic movement of people away from farms into cities and towns.  Previous studies have suggested that these may be related and data do exist to show childhood farm animal exposures and consumption of unpasteurized milk reduces the risk of childhood asthma and allergies.  But what about early-life farm exposures and adult asthma and allergic sensitization?  In this month’s issue of JACI, House and colleagues studied more than 3000 farmers and their spouses to help answer this question (J Allergy Clin Immunol 2017; 140(1): 249-256).

Specifically, they looked at 1746 farmers and 1555 spouses from Iowa and North Carolina enrolled in the Agricultural Lung Health Study.  They used questionnaires to identify current asthma and early-life farming exposure, and then measured blood levels of allergen-specific IgE, the type of antibody that suggests allergic sensitization to a given allergen.

After analyzing all the data, they found that exposure to a farming environment when still in the womb, living on a farm when born, exposure to farm animals before the age of 6 years, and drinking raw milk were all associated with a decreased risk of allergic sensitization. Among these, the strongest association was between the mother performing farm activities while pregnant and future atopy.   There was little correlation between these factors and asthma development in adulthood.

This study builds upon previous research supporting “the hygiene hypothesis,” that is, exposures to diverse types of germs early in life promotes immune tolerance and reduces the risk of allergies throughout life.  This information can guide further research in the prevention and treatment of allergies.