Asthma is a common disease where the airways become inflamed and overly reactive, and early-life gut bacteria may play a role in increasing asthma risk. Now, researchers have found that gut microbes can directly affect lung function and alter airway responsiveness. 

The findings, published in mBio, highlight the importance of early-life gut microbes in shaping lung health and add to evidence that microbiota composition can influence asthma risk.

Previous studies have shown that babies with less diverse gut microbiota are more likely to develop asthma and allergies, but it’s unclear which bacteria influence asthma risk and how they affect the immune system.

Ivon Moya Uribe at Michigan State University and her colleagues set out to investigate how gut microbes affect asthma development by analyzing stool samples from 60 three-month-old infants. 

Lung function

Infants with higher levels of bacteria such as Escherichia coli-Shigella and Bifidobacterium were more likely to develop eczema by age 1-3 years, while those with more Bacteroides bacteria were less likely to have eczema. Eczema is a condition that typically begins in infancy, followed by food allergies, allergic rhinitis, and asthma.

Next, the researchers transplanted gut microbes from the two groups of infants—those with high levels of eczema-related bacteria and those with protective bacteria—into germ-free mice.

Mice that received human-derived microbiotas had high levels of pro-inflammatory and allergy-exacerbating bacteria. When exposed to allergens such as dust mites, these mice had high levels of immune molecules associated with allergic responses and showed worse lung function, including increased airway stiffness, compared to animals with a typical mouse microbiota. 

Unclear mechanisms

Although the presence of specific bacteria—such as pro-inflammatory microbes—appeared to impair lung function, the researchers found no differences in lung function or allergic airway responses between mice that received the microbiota from infants with high levels of eczema-related bacteria and those that received the microbiota from infants with protective bacteria.

Even microbes thought to be protective caused alterations in the mice’s lung function, the researchers found. These results, they say, reject the hypothesis that one microbiota would result in less severe allergic reactions.

The findings, the authors add, suggest that gut microbes alone may affect lung function and airway resistance, but further research is needed to clarify the mechanisms behind these effects.