Biology

Why living with dogs protects against allergies

Pooch

Pooch protection (Photo credit: kevin dooley)

Household dog dust alters gut microbes to protect against respiratory ailments in mice

Own a dog? Then put down your duster and turn off the vacuum cleaner. Your household dust could be protecting you from allergies, thanks to your furred friend. As unsavory as it sounds, consuming small amounts of dog-microbe-laden dust could keep you breathing easy, according to research carried out in mice.

Allergy researchers have known for years that kids who are raised with a family pet or on a farm are less likely to develop asthma and allergies than kids raised animal-free. Research led by Susan Lynch at the University of California, San Francisco now provides evidence for the mechanism behind this protective effect.

The study, published this week in the Proceedings of the National Academy of Sciences, exposed mice to dust taken one of two locations: the first, a house with a resident pooch; the second, a less dusty pooch-free abode. To test whether the dust had a protective effect, the researchers fed mice the dust and then challenged them with cockroach allergen to elicit an allergic reaction.

Mice fed the dog dust had less inflammation in their lungs and a more muted immune response to the cockroach allergen compared to mice fed the regular house dust or no dust. A similar experiment using the egg white protein ovalbumin as the allergen showed similar results.

To determine what component of the dog dust could be exerting this immune-tempering effect, the researchers turned their attention to the microbes in the dust. Whereas the dog dust contained measurable amounts of bacteria, the regular dust was relatively microbe free.

The gastrointestinal tract contains an overwhelming array of resident bacteria that form complex microbial ecosystems. When the researchers surveyed the gut microbes of the dog dust-fed and regular dust-fed mice, they found that the microbial communities differed in composition. The gut microbiota of the dog dust-fed mice was particularly enriched in a particular bacterial species, Lactobacillus johnsonii.

This is not the first time that L. johnsonii has cropped up in the scientific literature as a handy microbe to have around. In rats, L. johnsonii can delay the onset of type I diabetes, and mice dosed with L. johnsonii during weaning are protected against developing atopic dermatitis.

Mice fed a dose of L. johnsonii and then exposed to the cockroach allergen showed a muted immune response compared with control mice. The protective effect of this single microbe was not quite as large as the dog dust, indicating that other components of the microbial cocktail in the dog dust may also have immune boosting powers.

In a further test of the importance of L. johnsonii for respiratory health, the researchers challenged mice with respiratory syncytial virus, a virus known to be a risk factor for developing childhood asthma. Once again, the immune response was dampened in mice fed L. johnsonii compared with controls.

The results fit well with mounting evidence that disrupting the complex community of microbes in our gut can affect our health. Antibiotics taken early in life can increase the chances of developing childhood asthma. So, too, can caesarian delivery, which alters the slew of microbes that make up some of the first colonizers of a baby’s intestine.

The study also adds to the growing body of research that is putting gut microbes in a central role when it comes to priming our immune system, and not just in our gut. The researchers found no evidence of L. johnsonii in the lungs of mice dosed with the bacteria, even though this is where the damped immune response was observed.

The specific details of what’s going on in the gut that results in long-range protection against allergies are yet to be unravelled. But the idea that we could one day manipulate our gut microbiota to ward off illness seems tantalizingly close. In the meantime, our best bet could be wagging its tail at our feet right now.

Reference: Fujimura KE, Demoor T, Rauch M, Faruqi AA, Jang S, Johnson CC, Boushey HA, Zoratti E, Ownby D, Lukacs NW & Lynch SV (2013) House dust exposure mediates gut microbiome Lactobacillus enrichment and airway immune defense against allergens and virus infection. PNASdoi:10.1073/pnas.1310750111

This original article was published by Dyani Lewis at United Academics.

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