Could reengineering the gut microbiome of neonates prevent asthma and allergies?
Recent studies have shown that early exposure to some microbes can benefit health.
A 2014 study - by Susan Lynch of the University of California-San Francisco (UCSF), co-senior author of the current study, and colleagues - found that children are more likely to develop asthma if they grow up in a house with fewer bacterial species in the dust and more fungi.
Breastfeeding, vaginal births, and having a pet dog at home have all been shown to protect against allergies and asthma.
Previous research has indicated that, at 3 months, children with low levels of four key types of gut bacteria are far more likely to have early warning signs of asthma by the age of 1 year, compared with infants with normal levels of these bacteria.
Certain microbes increase asthma risk threefold
Now, researchers at UCSF and the Henry Ford Health System in Detroit, MI, have linked a particular pattern of microbes in the guts of 1-month-old infants to a threefold higher risk of developing allergic reactions by the time they are 2 years old and asthma by 4 years of age.
- 17.7 million adults, or 7.4 percent, have asthma in the U.S.
- 6.3 million children up to age 17 years have asthma, or 8.6 percent
- 3,360 asthma-linked fatalities occurred in 2013.
In 2003, the lab of Christine Cole Johnson, co-senior author of the current study, started tracking early life risk factors for asthma in children born in Detroit. They monitored the infants to the age of 1 year, tested them for allergies at the age of 2 years, and for asthma at 4 years.
The scientists also collected and preserved stool samples from the infants. Recently, the availability of new genetic technology has made it possible to analyze these samples for microbiome features that might link to asthma later in life.
The researchers studied the gut microbes of 130 1-month-old infants. The results fell into three clear groups, each with different types of bacterial and fungal species.
On matching the results of the analyses with the 2- and 4-year follow-up data, 11 infants had three times the risk of developing allergies and asthma, compared with the others. This group also lacked certain normal gut bacteria, but they had higher levels of certain fungal species.
The researchers then looked at the metabolic byproducts of the microbes in the stool samples. These molecules provide clues about what the microbes have been doing in the gut.
Infants with asthma risk appear to lack certain lipids
Newborns with healthy microbiomes have a range of molecules in their gut that can reduce inflammation, including a set of fat molecules that are thought to nourish T-regulatory immune cells. These cells keep the rest of the immune system in check.
The infants who were prone to allergies and asthma did not have these molecules. They had different fats, including one that has been linked to asthma in adults.
The authors propose that the lack of these cells leads to a hyperactive immune system, and eventually, chronic asthmatic inflammation of the lungs.
Lynch believes that new ways to prevent allergies and asthma could follow. Currently, a child does not receive a diagnosis of asthma until the age of 6 or 7 years, and it can only be controlled with medication because there is no cure.
The current findings suggest that, if signs of allergic asthma appear in the gut microbiota early in life, some intervention could alter the microbes so that the disease will not develop in the future.
"We have been working for over a decade, trying to figure out why some children get asthma and allergies, and some don't. It seems that the microbial communities within the body could be the keystone to understanding this and a number of different immune diseases."
Christine Cole Johnson, chair of public health sciences in the Henry Ford Health System
Dr. Homer Boushey, a member of the research team, points out, "Asthma has doubled in prevalence in modern westernized societies about every 20 years for the past 60 or 70 years, so an effective strategy for prevention is becoming an urgent need for public health."
Keeping a dog may help
When they looked at environmental and socioeconomic factors, the team found that males are more susceptible to a high-risk microbiome, and they confirmed that having a dog decreases the risk.
Lynch says that humans live together with microbes, and that the genomes of some microbes are beneficial, especially in the early stages of life.
"But lifestyles have changed dramatically over the past several decades: We've significantly reduced our exposure to these environmental microbes our bodies rely on. Having a dog track the external environment into the home may be just one way to improve the breadth of microbes babies are exposed to in very early life."
Susan Lynch, UCSF associate professor of medicine