Inhaled Microbes, Allergy Development and Protective Lactobacillus Johnsonii

I typically don’t gush over mouse studies. Mice are not people. But mouse models are invaluable for defining important scientific concepts. So today I’m going to highlight a mouse study on allergy risk that I find very intriguing.

Observational studies have shown that early life exposure (exposure of pregnant women can protect their babies) to microbes in a variety of situations (such as exposure to livestock or dogs, or growing up with numerous siblings) is associated with a decreased risk of asthma. Conversely, disruption of normal colonization processes (such as antibiotic use and C-section delivery) is associated with increased risk of allergy. Some gut microbiota changes also track with asthma risk. For example, one study showed a greater risk of developing childhood allergic diseases when infant feces contained higher levels of Escherichia coli or Clostridium difficile.

With these observations as a backdrop, researchers at University of California San Francisco investigated how the air we breathe may impact GI microbiome composition and airway disease outcomes (Fujimura et al. 2014). They collected dust from 2 homes, one without a dog, the other with an indoor/outdoor dog. Using a sterile process, they vacuumed a 3′ × 3′ area for 3 min (four times as much dust was collected from the home with the dog). They then exposed mice to the collected house dust, and found that their immune response to these airway allergens was down-regulated in mice treated with the dust from the home with a dog. Observed changes included reduction in the total number of airway T cells, down-regulation of Th2-related airway responses, reduced mucin secretion and an altered microbiome of the cecum. Specifically, Lactobacillus johnsonii levels were higher in mice exposed to dust from the house with a dog. Researchers found that giving mice an oral dose of live L. johnsonii (3.9×107 CFU) was also protective, downregulating antibody responses and airway inflammation.

This study is unique in that it evaluates the impact of inhaled exposures, rather than dietary ones. But it reinforces that protection can also be achieved through exposure to the right dietary probiotics. The authors conclude that this study suggests that “GI microbiome manipulation represents a promising and efficacious therapeutic strategy to protect individuals against both pulmonary infection and allergic airway disease.”

Let’s hope the findings can be confirmed in humans.

Reference:

Fujimura KE, Demoor T, Rauch M, Faruqi AA, Jang S, Johnson CC, Boushey HA, Zoratti E, Ownby D, Lukacs NW, Lynch SV. House dust exposure mediates gut microbiome Lactobacillus enrichment and airway immune defense against allergens and virus infection. Proc Natl Acad Sci U S A. 2014 Jan 14;111(2):805-10.