It is widely believed that children who grow up in environments rich in biodiversity—on farms, in homes with pets, and in rural areas in general—are less likely to suffer from allergies. But why does this happen?
American researchers have found an answer. It turns out that exposure to a variety of microbes and proteins early in life helps build a broad immune memory and stimulates the production of specific antibodies that can block allergic reactions later on. According to the scientists, instead of overreacting to harmless allergens (such as ragweed, cats, peanuts, etc.), a well-trained immune system responds in a more balanced way.
These findings could help develop more effective allergy prevention strategies, encouraging early interaction with natural environments and the use of new treatments that strengthen protective immune responses rather than simply suppress symptoms. The study was published in the journal Nature.
“We wanted to test the hypothesis that living in a less sterile environment protects against allergies,” says Ruslan Medzhitov, Professor of Immunobiology and the study’s lead author. “The main question we aimed to answer was: what happens to the immune system when a person lives in a natural environment and is exposed to a large number of microbes?”
To investigate this, the researchers compared two groups of mice. One group consisted of animals raised in a microbe-rich environment—similar to mice living in natural habitats, according to Scientific Russia. The second group included laboratory mice raised in sterile conditions. Both groups were exposed to allergens, after which the scientists measured allergic reactions, antibody production, and immune cell activity.
The researchers stimulated the mice’s immune systems by exposing them to common infectious agents, as well as complex food allergens such as soy, peanuts, and peas. They also examined at what age the mice were most likely to develop allergies by comparing their condition in early life and adulthood.
It was found that mice raised in natural conditions were largely protected from severe allergic reactions compared to laboratory mice. These mice had a kind of immune memory that allowed them to cope with allergens they had never encountered before. This cross-reactive immune memory shifts the response away from allergy-causing antibodies (IgE) toward protective antibodies (IgG), which do not trigger allergic reactions.
“Wild mice are exposed to all kinds of microorganisms but do not get sick. They represent the normal state of an animal—and of humans up to about 100 years ago,” said Medzhitov. “Essentially, we found that with normal exposure to microbes and other antigens, the immune system functions very differently compared to sterile mice, whose immune system is clearly not in a normal state.”
In overly “clean” environments, the immune system may be insufficiently trained and more prone to malfunction. In modern society, the number of allergy cases has risen sharply, and this study shows that the environment—not just genetics—plays an important role in the development of allergic reactions.
“Thanks to industrialization and the use of antibiotics, disinfectants, hygiene products, and vaccination, we are increasingly protected from truly dangerous microbes, which is a good thing,” Medzhitov adds. “But the trade-off is that our immune system remains untrained and unprepared, so harmless exposures can trigger pathological allergic reactions.”
New data also suggest that exposure to allergens and the production of IgG antibodies (immunoglobulin G)—the most common antibodies in the blood—may help in treating existing allergic diseases. According to the researchers, the study also sheds light on the role of the environment in the development of autoimmune disorders.
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