Author: Maria Zagorulya
Institution: University of Rochester
According to new scientific research, having a puppy at home can save us from allergies. The immunology project was coordinated by Susan Lynch, an associate professor with the Division of Gastroenterology at UC San Francisco, and Nicholas Lukacs, a professor with the Department of Pathology at the University of Michigan.
The multi-disciplinary group of researchers from UCSF, the University of Michigan, Henry Ford Health System and Georgia Regents University, discovered that exposure to dog dust reduced the risk of young mice developing allergies.
In the experiment, dust was collected from two houses - one with no animals and one with a dog that partly lives outdoors. It was then mixed with water and fed to young mice. These mice were then exposed to cockroach or egg protein, two substances which are known to cause allergy symptoms in rodents and humans. The results published in the Proceedings of the National Academy of Sciences demonstrate that mice consuming dust collected from dog-associated houses have significantly lower levels of asthmatic lung inflammations, as opposed to mice exposed to no dust or dust from houses without dogs.
"Early life exposure to dogs, and cats to a lesser extent, can protect against allergic sensitization, and this has been shown in epidemiological studies," says Lynch. Now, as her immunology research demonstrated that dog dust offers a degree of protection from harmful effects of allergen exposure, there is increased evidence supporting the hypothesis.
In an attempt to identify the precise component responsible for the apparent anti-allergy properties of dust, scientists examined the types of bacteria present in the mouse guts before and after feeding them the dust. One microbe, Lactobacillus johnsonii, was most abundant in mice exposed to dog’s dust. When the bacterium was given separately to mice, rodents’ allergic response diminished. These findings suggest that L. johnsonii plays an important role in preventing asthmatic symptoms, which occur in response to allergens as well as respiratory syncytial virus infection – an infection that correlates with high asthma risks in infants.
“Our studies suggest that [this bacteria] is a critical mediator of airway protection against environmental insults,” Lynch says. Further experiments showed that decreased allergic response in protected mice was the result of fewer and less active immune cells that are normally involved in asthmatic reactions. However, on its own L. johnsonii generated less allergic protection than dog dust, indicating that there must be some other species affecting the mouse gut microbial environment, and contributing to increased strength of mice’s immune systems and offering higher allergy protection.
Lynch and colleagues built their research upon the results of previous investigations. In 2010, the research group showed that dogs that are allowed to roam both indoors and outdoors bring environmental microbes into the house and that some of these bacterial species are actually present in the human gut. In 2011, Lynch published a paper describing the influence of gut microbes on the human immune system. Linking the two ideas together, Lynch and Lukacs “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 researchers’ focus on immune diseases is not surprising. Extremely rare in the beginning of the 20th century, allergic conditions including hay fever, asthma, eczema, food allergies and reactions to bee-stings are practically omnipresent today. The increasing prevalence of allergies in the modern society has stimulated a good deal of biomedical research on the causes and possible therapies for the condition.
One of the proposed explanations for the rise in allergies is the hygiene hypothesis, which argues that the cleanliness of our modern lifestyle has caused our immunity to become less protective and more susceptible to toxins as well as other foreign substances including allergens. The results of the study by Lynch and her colleagues support this theory, suggesting that exposure to dog dust at an early age leads to decreased vulnerability to allergic reactions, specifically asthma, due to the consequent changes in the organism’s gastrointestinal microbiome.
“This is likely to be one mechanism through which the environment influences immune responses in early life,” Lynch speculates, “and it is something we are currently examining using human samples in a large multi-institutional collaborative study funded by the NIAID.”
Lynch believes that "gut microbiome manipulation represents a promising new therapeutic strategy to protect individuals against both pulmonary infection and allergic airway disease.” Perhaps, after more clinical studies this method of therapy will be able to prevent asthma and provide relief to those suffering from the allergic lung disease.
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