Alex Eben Meyer
For almost 40 years, researchers have known that those children who grow up on farms, in rural areas, or in homes with pets are significantly less prone to allergies.
New research by Yale scientists has for the first time identified how this mechanism works. The study, which was published earlier this year in Nature, compared mice from a pet shop, who’d been exposed to a wide range of microbes and allergens, to lab mice, who’d been raised in a sterile environment. When exposed to an allergen, the lab mice were much more likely to have severe reactions. The other mice, by contrast, rarely developed allergies. “The wild mice were completely protected,” says Ruslan Medzhitov, a professor of immunobiology at the Yale School of Medicine and the senior author of the study. “It was striking.”
To understand why, Medzhitov and his colleagues analyzed antibodies in the animals’ blood. Antibodies are proteins that alert the immune system about invasive cells. The researchers found that the two groups had similar levels of an antibody called IgE, which tends to trigger a strong allergic reaction. But the wild mice had much higher levels of another antibody, IgG, which tamps down on the immune response. Medzhitov says that in the wild mice, the higher levels of IgG ensured that IgE didn’t overreact.
He suspects what happened with the lab mice is what’s happened with humans. Over the past 150 years, improved sanitation and medical care have sharply reduced our exposure to pathogens and allergens. The result: a huge reduction in death and disease. However, our immune systems have become less familiar with allergens, and so tend to respond inappropriately when they appear.
The next step, Medzhitov says, is to explore ways to adjust the modern human immune system so that it doesn’t hit the panic button every time it detects a peanut or some pollen. “It’s not practical to make everyone go live on a farm,” he says. “So we need to find a way to hack the system.”
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