Environmental Factor

Environmental Factor

Your Online Source for NIEHS News

September 2016

Microbe-rich environments may trigger immune system, prevent asthma

Amish children growing up on farms that use animals have an immune response that may prevent asthma, according to a new study supported in part by NIEHS. The research was published Aug. 3 in the New England Journal of Medicine (NEJM).

The study compared children from two U.S. farming communities, one Amish and the other Hutterite. The two communities have many similarities, including shared genetic heritage, but the Amish use livestock for fieldwork and transportation, and the Hutterites practice industrialized farming with machinery. Previous studies have shown that asthma is rare among Amish children, whereas it is present at typical U.S. levels in Hutterite children.

The researchers saw a key difference in how the children’s immune systems functioned. Based on the types of cells and the chemical signals activated, the Amish children actively used their innate immune systems (see sidebar). This response was weaker in the Hutterite children.

“The study augments prior work showing the significant role our environmental exposures play in asthma,” said Peter Thorne, Ph.D., in a University of Iowa press release. Thorne is a co-author of the study and director of the NIEHS-funded Environmental Health Sciences Research Center at the University of Iowa. “The big advance is how our study beautifully demonstrated the key role of innate immunity in asthma in two rural populations with similar genetics.”

Microbial richness in Amish homes

Thorne’s research team used air samplers that did not require electricity in the Amish and Hutterite homes to measure airborne particles and bacterial indicators. The researchers found that the types of bacteria in the two groups of homes were different, and that the levels of endotoxin, a bacterial indicator, were nearly seven times higher in Amish homes.

“The striking differences found in endotoxin levels support the notion that the Amish indoor environment is much richer in microbial exposures than the Hutterite environment,” the authors wrote.

Rather than triggering allergic responses, exposure to microbe-rich farm dust seems to prompt the innate immune response to generate a low level of inflammation that prevents the emergence of asthma, according to a NEJM editorial that accompanied the paper. Questions remain as to whether continuous exposure to the dust is required for this protective effect.

Extensive evidence for innate immunity

In a final piece of the puzzle, the researchers exposed mice to dust from the homes, while inducing allergic asthma. When the mice were exposed to Hutterite house dust, their airways became inflamed through an allergic response. However, mice exposed to Amish house dust were protected by an activated innate immune response. And when the scientists blocked key chemical signals for the innate immune response in the mice, the protective effect of the Amish house dust disappeared.

“When we administered extracts of the two types of dust to mice, we were able to reproduce the differences in respiratory allergy that we observed in the Amish and Hutterite children,” Thorne explained.

The findings support the hygiene hypothesis, or the theory that children who grow up in cleaner environments without significant microbial exposures are more likely to develop allergic disease, like asthma, according to Claudia Thompson, Ph.D., head of the NIEHS Population Health Branch.

“We’ve seen previous evidence that growing up on small family farms can protect against asthma, and that microbial exposures likely play a protective role, but it wasn’t clear exactly why,” said Thompson. “This groundbreaking study indicates that the innate immune system is a critical part of this protection.”

Citations: Stein MM, Hrusch CL, Gozdz J, Igartua C, Pivniouk V, Murray SE, Ledford JG, Marques dos Santos M, Anderson RL, Metwali N, Neilson JW, Maier RM, Gilbert JA, Holbreich M, Thorne PS, Martinez FD, von Mutius E, Vercelli D, Ober C, Sperling AI. 2016. Innate immunity and asthma risk in Amish and Hutterite farm children. N Engl J Med 375(5):411-421.

Chatila TA. 2016. Innate immunity in asthma. N Engl J Med 375(5):477-9.

(Virginia Guidry, Ph.D., is a technical writer and public information specialist in the NIEHS Office of Communications and Public Liaison and a regular contributor to the Environmental Factor.)


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