Pet dogs may protect babies against asthma, allergies

Babies who live in homes with a pet dog are less likely to develop asthma and allergies later in childhood, scientists have found.
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, a new study has found.
Researchers led by Susan Lynch, associate professor with the Division of Gastroenterology at the University of California - San Francisco and Nicholas Lukacs, professor with the Department of Pathology at the University of Michigan also identified a specific bacterial species within the gut that is critical to protecting the airways against both allergens and viral respiratory infection.

The results were obtained in studies of mice challenged with allergens after earlier exposure to dust from homes with dogs, but the results also are likely to explain the reduced allergy risk among children raised with dogs from birth.
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 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 treat existing cases, she said.

The team had previously demonstrated that the presence of a dog that roams both inside and outside was linked with a more diverse house dust microbiome that was enriched for species found in the gastrointestinal tract of humans.
The study is published in the Proceedings of the National Academy of Sciences (PNAS).