The four bugs that protect us from asthma

Something about modern living sends asthma rates soaring. In Western countries we saw it happen from the 1960s to the 1990s. Now we’re seeing the trend repeat in developing countries as they westernise.

The latest thinking is that clean modern urban lifestyles don’t expose us to the right sorts of microbes to train the immune system. Absent the training, our immune system is likely to overact to provocateurs like house dust. One key spot where immune cells and microbes mix is the gut. So is it possible to identify what an ideal gut bacterial community should like? A team of Canadian researchers embarked on that mission and came back with an astonishing result: just four species of bacteria provide protection against asthma. The report was published in Science Translational Medicine in September.

Thousands of species of bacteria inhabit the human gut, so identifying what the right bacterial community should look like is daunting. The Canadian team took courage from state-of-the-art techniques that allowed them to read the DNA signatures of bacteria in the poo of three month old Canadians – 319 of them.  Their mothers had obligingly enrolled in the Canadian Healthy Infant Longitudinal Study (CHILD). The infants were followed for a year to see which of them became allergic and wheezy – strong predictors of asthma. It turned out the wheezy babies were more likely to be missing four types of bacteria: Lachnopsira, Veillonella, Faecalibacterium and Rothia. Could only four types of bacteria protect against asthma?

Yes, as the team showed with mice. A pregnant mouse was raised in a sterile environment. Her gut was inoculated with microbes from the poo of a three month old human infant with low levels of the four bacteria. The mouse pups developed asthma. But if the mouse mother’s inoculum was supplemented with the four bacteria, her pups were protected!

Could a variation of this treatment work for human infants, perhaps by introducing these bacteria to pregnant mothers? “That’s the question we are addressing now,” says Stuart Turvey a paediatric immunologist at the University of British Columbia and co-author of the study. The opportunity for these bacteria to modify the immune system from an allergic state to a non-allergic one, seems to lie within the first 100 days of life. While the microbial communities of the three month old babies showed differences, by the time they were a year old, those differences had almost vanished.

So early life exposure may be key, says Turvey, a finding that matches what was found in the Bavarian farm studies.

So could you pick up these four types of bacteria on a Bavarian farm? The Canadian team doesn’t know. The one bit of information they do have, says Turvey, is that some of them produce endotoxin, the fragment of the bacterial wall that helps train the immune system (see main article). They also produce acetate in the gut. This short chain fatty acid travels through the bloodstream, and has also been shown to help modulate the immune system.

Could the solution to the asthma epidemic could be as easy as restoring the ecological balance of  a baby’s microbial community with four bugs? “While this research is still in its infancy, it raises an exciting possibility,” says Rhys Allan, an asthma researcher at Melbourne’s Walter and Eliza Hall Institute.