It’s long been thought that when children grow up in places like farms, rural areas or even homes with many pets—places that have greater biodiversity—then those kids are less likely to develop allergies. A new study has sought to determine whether that is true and if so, why. Although it used a rodent model, this work confirmed that when youngsters are exposed to a diverse range of protein and microbes early in life, a broad immune memory arises along with the production of an antibody that can prevent allergic reactions later in life. This study could help scientists create better allergy prevention strategies that boost protective immune responses instead of suppressing immune function. The work has been reported in Nature.
"We wanted to test this idea that living in a less clean environment protects you from allergies," said first study author Ruslan Medzhitov, a Professor oat Yale School of Medicine. "The main question we wanted to answer was what's happening to the immune system when you're in a natural environment and exposed to a lot of microbes?"
In this work, the investigators used a mouse model that had been divided into two groups; one was raised in an environment that was similar to the natural world and contained many diverse microbes; the other was raised in a sterile environment. Both groups of mice were then exposed to allergens like infectious agents, as well as pea, peanut, and soy.
The scientists assessed the antibodies, allergies, and immune cell function in the mice, and analyzed the timing of allergy development when it occurred. They determined that mice that were raised in more ‘natural’ environments had virtually no problems with allergies compared to mice raised in a clean, sterile environment.
The immune memories of naturally-raised mice could deal with allergens that clean-raised mice had not encountered, and their responses were less likely to lead to the production of antibodies like IgE (Immunoglobulin E) that can spur allergies, and more likely to create antibodies that are protective and do not trigger allergies, like IgG (Immunoglobulin G).
"The natural mice get all kinds of microbial exposures, but they're not sick. They represent what is the normal state of the animal, and of humans up until about 100 years ago," noted Medzhitov. "Basically, we found that this normal exposure to microbes and other antigens builds up a very different state of the immune system compared to what we see in the clean mice, whose systems are clearly not normal."
Immune systems that develop under cleaner environments may be undertrained, making excessive reactions more likely, suggested the scientists.
Allergen exposure and IgG antibodies could potentially help treat existing allergies, they noted.
"With industrialization and the use of antibiotics, sanitization, hygiene products, vaccinations, and so on, we're increasingly protected against truly dangerous microbes, which is great," said Medzhitov. "But the tradeoff is that our immune system is in this untrained, unprepared state, and otherwise harmless exposures trigger a pathological allergic response."
Sources: Yale University, Nature