How farm life can prevent allergies

Preventing many allergies could be as simple as taking a breath — of farm dust.

Dust from dairy farms switches on an anti-inflammatory enzyme in the lung cells of mice, researchers report in the Sept. 4 Science. The enzyme keeps the immune system from overreacting to common allergens, such as house dust mites, the team found.

It’s the first time researchers have pinned down a specific molecule that explains how farm dust can prevent allergies, says immunologist Donata Vercelli of the University of Arizona in Tucson. “This won’t be the end of the story, but it’s certainly a good beginning,” she says.

Scientists have known for years that farm life seems to protect kids from developing such allergies as asthma and hay fever. Contact with animals, drinking raw milk and breathing farm air all could play a role. But no one knows exactly how.

Pulmonary physician Bart Lambrecht of Ghent University in Belgium and colleagues collected dust from stables and dairy farms in Germany and then let some mice inhale a tiny bit of dust every other day for two weeks. These mice then sniffed house dust mites, an allergen that usually triggers asthma in mice.

Mice that had been breathing farm dust didn’t get asthma. A genetic analysis of the cells lining the mice’s lungs revealed that Tnfaip3, the gene for making the enzyme A20, had been switched on. A20 tells lung cells to chill out, so they don’t fire up the immune system unnecessarily. The enzyme removes ubiquitin, a molecule that sticks to proteins and can signal cells to dial up inflammation.

But A20 isn’t called to duty unless farm dust is around, the researchers found. The dust ingredient that protects against allergies may be bits of bacteria called endotoxin. A separate experiment exposing mice to just endotoxin also protected the mice from asthma. In real life, the bits of bacteria could come from dried-out cow manure that has crumbled to dust, Lambrecht says. Wind passing over farms picks up the tiny particles and lofts them into the air. “We’re used to breathing this in,” he says. “There’s nothing wrong with it.”

The team’s mouse findings could translate to humans. Surveying a database with medical and residential information on 1,707 children from four European countries uncovered the same genetic link between farm dust and allergies that the researchers found in mice.

Lambrecht thinks that some kids may live in houses that are just too clean. Nowadays, people use antiseptic soaps just to scrub floors and sinks, he says. “This is the stuff they use to clean operating rooms. There’s no reason why our kitchen sinks should be sterile.”

Stewart Levine of the National Heart, Lung, and Blood Institute in Bethesda, Md., says Lambrecht and colleagues’ work offers a new mechanism for explaining how cells in the lungs can prevent allergic airway inflammation. “That’s the really novel and important part.”

But, he says, “I don’t know if I would take my kid and put them in a barn based on this paper.”