Health experts have known for years that kids who grow up on a farm have fewer incidences of allergies and asthma than city kids, but continued research is helping them better understand the connection between the immune system and microbes only found in that setting.
A study published in the New England Journal of Medicine compared 30 Amish children and 30 Hutterite children from two farming groups in North Dakota. Researchers chose these children because asthma is rare among the Amish but common among the Hutterites, even though the groups have similar genetic backgrounds and diets and little exposure to tobacco smoke, polluted air and indoor pets. The one key difference lies in their farming methods: The Amish shun electricity and industrialization, while the Hutterites embrace it. Because of this, the children are exposed to different microbes.
"We never thought we would see a difference," Carole Ober, an author of the study and the chairwoman of the department of human genetics at the University of Chicago, told The New York Times. But to their great surprise, "we saw whopping differences with very, very different cell types and cell numbers."
The Amish children all had a large proportion of neutrophils, white blood cells that are part of the so-called innate immune system. The Amish kids' neutrophils "were newly emerged from their bone marrow, evidence of a continual low-grade reaction to microbial invaders," the Times reported. In contrast, the Hutterite kids had "old" neutrophils, and researchers found their blood was full of another type of immune cell, eosinophils, which provoke allergic reactions.
"I keep saying if everyone would just put a cow in their house, no kid would have asthma, but that's not very practical," Ober told Live Science. Instead, Ober envisions an air mister parents could use to spray the beneficial microbes into the air.
The link from gut to immune system
Scientists from The Ohio State University took note of this connection and took it a step further. In a small study of Ohio babies, they found that Amish babies in rural settings had much more good bacteria than urban babies, which wasn't surprising given the previous studies. But they also found evidence that a healthier gut microbiome may lead to healthier development of the respiratory immune system, according to a press release from OSU.
They made this connection with the help of young pigs. They essentially did a fecal transplant, placing the Amish babies' poop into the intestines of newborn pigs, essentially testing the hygiene hypothesis with the help of pigs, which have an immune system more similar to humans. The results were an increased development of immune cells, particularly lymphoid and myeloid cells in the intestines.
"We wanted to see what happens in early immune system development when newborn pigs with ‘germ-free’ guts are given the gut microbes from human babies raised in different environments," said Renukaradhya Gourapura, co-lead author of the study. "From the day of their birth, these Amish babies were exposed to various microbial species inside and outside of their homes."
The research was published in Frontiers in Immunology.
A closer look at farm dust
Researchers at two Belgian universities collaborated on a study that looked at one particular aspect of farm living — the dust. They found that a bacteria detected in farm dust might initiate an immune system response that reduces the body's reaction to allergens and asthmatic triggers. Their work was published in the journal Science.
According to the Centers for Disease Control and Prevention, 6.8 million children in the U.S. have been diagnosed with asthma and about 17 percent of kids suffer from respiratory allergies to things like pollen and mold. But over the last few decades, health care providers have observed that kids who grow up on farms are much less likely to be affected by these conditions than their urban-dwelling peers.
So researchers have been looking at farm dust to better understand how it protects kids from respiratory problems. For the 2015 study, researchers exposed mice to bacteria found in farm dust. After two weeks, they exposed those mice to dust mites. They found that the mice who had been exposed to the bacteria were less likely to have an asthmatic or allergic reaction to the dust mites than the unexposed mice.
What's more, researchers found that when the mice were exposed to farm dust, they produced a protein in their lungs called A20. When they deactivated this protein, these mice had a normal allergic response to the dust mites.
Researchers confirmed these findings with human surveys where they found that people who suffer from allergies and asthma have a deficiency in A20 protein. Finally, they took a look at the kids growing up on farms who develop asthma and allergies. You guessed it — those kids have a mutation in their A20 gene that impedes the production of A20 protein.
By narrowing down the mechanisms behind certain asthmatic and allergic reactions, these researchers may have opened the door for the development of vaccines and treatment options for people who suffer from these conditions.
Editor's note: This story has been updated since it was originally published September 2015.