A new study has revealed why children's risk for developing allergies and asthma is reduced when they are exposed in early infancy to a dog in the household.
According to a new study by researchers led by Susan Lynch, PhD, associate professor with the Division of Gastroenterology at UC San Francisco, and Nicholas Lukacs, PhD, professor with the Department of Pathology at the U Michigan, exposure of mice to dust from houses where canine pets are permitted both indoors and outdoors can reshape the community of microbes that live in the mouse gut- collectively known as the gastrointestinal microbiome- and also diminish immune system reactivity to common allergens.
The scientists also identified a specific bacterial species within the gut that is critical to protecting the airways against both allergens and viral respiratory infection.
In their study the scientists exposed mice to cockroach or protein allergens. They discovered that asthma-associated inflammatory responses in the lungs were greatly reduced in mice previously exposed to dog-associated dust, in comparison to mice that were exposed to dust from homes without pets or mice not exposed to any dust.
Among the bacterial species in the gut microbiome of these protected mice, the researchers homed in on one, Lactobacillus johnsonii. When they fed it alone to mice, they found it could prevent airway inflammation due to allergens or even respiratory syncytial virus (RSV) infection. Severe RSV infection in infancy is associated with elevated asthma risk.
The researchers showed in this experiment that protection of the lungs' airways was associated with reduced numbers and activity of asthma-associated immune cells.
The level of protection with this single species was less than that obtained with the full complement of dust microbes from dog owners' homes, indicating that other, environmentally sourced bacterial species probably are necessary for full airway protection, Lynch said.
This result suggests that Lactobacillus johnsonii or other species of "good" bacteria might one day be used to reshape the gut microbiome in ways that can prevent the development of asthma or allergies, or perhaps even to treat existing cases, she said.
The study is published in the Proceedings of the National Academy of Sciences.
