Dogs and Allergies

Experts have suspected for some time that having dogs in the house may keep children from developing certain allergies, and now researchers have a better idea why.

Susan Lynch, a scientist at the University of California, San Francisco, has discovered that dust collected from homes where dogs live leads to the development of gut bacteria that trigger an immune response in young mice. 

In a study published online today in Proceedings of the National Academies of Sciences, Lynch and her colleagues described how they tested for allergies in pre-adult mice. Rodents exposed to dust from a dog owner's home produced less mucous and fewer airway T-cells when they were later exposed to a cockroach allergen. T-cells help the body reduce inflammation and mucous caused by allergens. 

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“What we're finding is that allergens can tweak, in an indirect way or a direct way, how microbiomes influence these important immune cells,” said Dr. Kari Nadeau, an allergist at Stanford University who leads translational research and clinical studies for Packard Children's Hospital.

Nadeau told Healthline that Lynch's research is important as allergists try to understand the link between allergies and the bacteria that live in our stomachs.

Good Bacteria Protect Vulnerable Guts

In her experiment, Lynch found that mice exposed to the dog dust had a type of bacteria in their guts called Lactobacillus johnsonii. The scientists tried giving the control group a dose of the same bacteria. Both groups of mice were then protected against the cockroach allergen, but those that were exposed to the actual dust fared best.

Lynch told Healthline this means that the dog dust likely leads to the growth of many different types of bacteria in the gut. She hopes future research will lead to a better understanding of how Lactobacillus johnsonii protects the airways. It also may aid in the identification of other bacterial species that provide protection.

“The long-term aim is to leverage these studies to develop refined communities of bacteria that can be used therapeutically to treat or prevent against allergic asthma in humans,” Lynch said.

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Previous data has shown that children exposed to dogs early in life—and cats to a lesser extent—are less likely to develop allergic asthma. The theory is that dogs introduce organisms from the outside into homes, exposing children to germs and bacteria they otherwise might not experience until later in life.

“That's what we believe, but we'll do further studies to prove that the bacteria originate from the external environment and that the same species actually colonize the human gut,” Lynch said. “It should be noted that there is a time-dependent component to the protective effect of furred pets. They tend to be protective if present early in life, so it is more complex than simply having a pet in the home—the timing of pet exposure matters.”

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