Research Shows How Household Dogs Protect Against Asthma, Infection
Study Points to Changes in Gut Microbes
Children’s risk for developing allergies and
asthma is
reduced when they are exposed in early infancy to a
dog in the
household, and now researchers have
discovered a reason why.
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, 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 University of Michigan.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.
The study, funded by the National Institute of Allergy and Infectious Diseases (NIAID), is published online this week in the Proceedings of the National Academy of Sciences (PNAS)
and involves a multi-disciplinary group of researchers from UCSF, the
University of Michigan, Henry Ford Health System and Georgia Regents
University.
Dust Protects the Lungs' Airways
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, according to the study leaders.
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.
Gut Microbiome's Affect on Immune System
Lynch’s own work and research by several others in the
field has led her to become convinced that “the composition and function
of the gut microbiome strongly influence immune reactions and present a
novel avenue for development of therapeutics for both allergic asthma
and a range of other diseases.”
The current study demonstrates that changes in the gut
microbiome can have wide-reaching effects on immune function beyond the
gut, at sites elsewhere in the body, Lynch said.
The team had previously demonstrated that the presence of a
dog that roams both inside and outside was associated with a
significantly more diverse house dust microbiome that was enriched for
species found in the gastrointestinal tract of humans.
After teaming up with Lukacs, an expert on immune
responses in lung disease, Lynch said, “We set out to investigate
whether being exposed to a distinct house dust microbiome associated
with indoor/outdoor dogs mediated a protective effect through
manipulation of the gut microbiome and, by extension, the host immune
response.”
“The results of our study indicate that this is likely to
be one mechanism through which the environment influences immune
responses in early life, and it is something we are currently examining
using human samples in a large multi-institutional collaborative study
funded by the NIAID.” “Gut microbiome manipulation represents a promising new
therapeutic strategy to protect individuals against both pulmonary
infection and allergic airway disease,” Lynch said.
University of California San Francisco
