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WASHINGTON, Aug. 6 (Xinhua) -- It has been known for over a decade that growing up on a farm can protect against asthma, and a U.S. study now uncovered the specific aspects of farm life that are responsible for such protection.
The study, published this week in the New England Journal of Medicine, probed differences between two U.S. farming communities: the Amish of Indiana and the Hutterites of South Dakota.
It showed that substances in the house dust from Amish, but not Hutterite, homes were able to engage and shape the innate immune system in young Amish children in ways that may suppress pathologic responses leading to allergic asthma.
"The source of protection is not simply farming," study author Carole Ober, professor and chairman of human genetics at the University of Chicago, said in a statement.
The Amish and Hutterite farming communities in the United States, founded by immigrants from Central Europe in the 18th and 19th centuries, respectively, have similar genetic ancestry.
They share similar lifestyles and customs, such as no television and a Germanic farming diet. They have large families, get childhood vaccinations, breastfeed their children, drink raw milk and don't allow indoor pets.
Although both groups depend on agriculture, their farming practices differ, with the Amish retaining traditional methods, living on single-family dairy farms and relying on horses for fieldwork and transportation.
In contrast, the Hutterites live on large communal farms and use modern, industrialized farm machinery, which distance their young children from the constant daily exposure to farm animals.
Another striking difference is what Ober calls a "whopping disparity in asthma."
About five percent of Amish schoolchildren aged 6 to 14 have asthma. This is about half of the U.S. average for children aged 5 to 14, and one-fourth of the prevalence among Hutterite children.
To understand this disparity, the researchers studied 30 Amish children seven to 14 years old, and 30 age-matched Hutterite children.
Blood tests revealed the Amish had more and younger blood cells crucial to fight infections, known as neutrophils, and fewer blood cells that promote allergic inflammation, known as eosinophils.
When the researchers exposed lab mice to house-dust extracts from the two communities, they found the airways of mice that received Amish dust were protected from asthma-like responses to allergens.
In contrast, mice exposed to Hutterite house dust were not protected.
Further research showed that dust collected from Amish homes was "much richer in microbial products" than dust from Hutterite homes.
"Neither the Amish nor the Hutterites have dirty homes," Ober explained. "Both are tidy. The Amish barns, however, are much closer to their homes. Their children run in and out of them, often barefoot, all day long. There's no obvious dirt in the Amish homes, no lapse of cleanliness. It's just in the air, and in the dust."
To better understand how asthma protection was achieved, the researchers used mice that lack MyD88 and Trif, genes crucial for innate immune responses. In these mice, the protective effect of the Amish dust was completely lost.
The researchers hoped that the findings will allow the identification of relevant substances that will lead to completely novel strategies to prevent asthma and allergy.
"You can't put a cow in every family's house," Ober added, "but we may be able to protect children from asthma by finding a way to re-create the time-tested Amish experience."
