Common bacteria could help prevent food allergies

11:00am Tuesday 26th August 2014

content supplied by NHS Choices

"Bacteria which naturally live inside our digestive system can help prevent allergies and may become a source of treatment," BBC News reports after new research found evidence that Clostridia bacteria helps prevent peanut allergies in mice.

The study in question showed that mice lacking normal gut bacteria showed increased allergic responses when they were given peanut extracts.

The researchers then tested the effects of recolonising the mice's guts with specific groups of bacteria. They found that giving Clostridia bacteria (a group of bacteria that includes the "superbug" Clostridium difficile) reduced the allergic response.

The researchers hope the findings could one day support the development of new approaches to prevent or treat food allergies using probiotic treatments.

These are promising findings, but they are in the very early stages. Only mice have so far been studied, with a specific focus on peanut allergy and Clostridia bacteria. Further study developments from this animal research are awaited.

 

The hygiene hypothesis

One of the medical puzzles of recent decades is the sharp rise in allergic conditions. One theory that attempts to explain this trend is the hygiene hypothesis.

 

This is the idea that as people grow up in increasingly sterile, germ-free environments, their immune systems become oversensitive, mistaking harmless substances such as pollen or peanuts as a threat and triggering an allergic reaction.

 

This is not to say that being unhygienic is good for you. Read more about whether we are being too clean for our own good.

Where did the story come from?

This study was conducted by researchers from the University of Chicago, Northwestern University, the California Institute of Technology and Argonne National Laboratory in the US, and the University of Bern in Switzerland.

Funding was provided by Food Allergy Research and Education (FARE), US National Institutes of Health Grants, the University of Chicago Digestive Diseases Research Core Center, and a donation from the Bunning family.

It was published in the peer-reviewed journal PNAS.

BBC News gave a balanced account of this research.

 

What kind of research was this?

This was an animal study that aimed to see how alterations in gut bacteria are associated with food allergies.

As the researchers say, life-threatening anaphylactic reactions to food allergens (any substance that generates an allergic response) are an important concern, and the prevalence of food allergies appears to have been rising over a short space of time.

This has caused speculation about whether alterations in our environment could be driving allergic sensitivity to foods. One such theory is the "hygiene hypothesis" (discussed above).

This is the theory that reducing our exposure to infectious microbes during our early years - through overzealous sanitisation, for example - deprives people's immune systems of the "stimulation" of exposure, which could then lead to allergic disease. 

An extension of this theory is that environmental factors - including sanitation, but also increased use of antibiotics and vaccination - have altered the composition of natural gut bacteria, which play a role in regulating our sensitivity to allergens. It has been suggested that infants who have altered natural gut bacteria could be more sensitive to allergens.

This mouse study aimed to examine the role of gut bacteria in sensitivity to food allergens, with a focus on peanut allergy.

 

What did the research involve?

The researchers investigated the role gut bacteria plays in sensitivity to food allergens in different groups of mice. The research team studied mice born and raised in a completely sterile, bacteria-free environment so they were germ free.

Another group of mice were treated with a mixture of strong antibiotics from two weeks of age to severely reduce the variety and number of bacteria in their gut.

These groups of mice were then given purified extracts of roasted unsalted peanuts to assess their allergic response.

After looking at the allergic reactions in the germ-free and antibiotic-treated mice, specific groups of bacteria were reintroduced into their gut to see what, if any, effect it had on their allergic response.

The researchers focused on reintroducing Bacteroides and Clostridia groups of bacteria, which are normally present in mice in the wild.

 

What were the basic results?

Faecal samples taken from the antibiotic mice were found to have a significantly reduced number and variety of gut bacteria. These mice also had increased sensitivity to peanut allergens, demonstrating an increased immune system response that produced antibodies specific to these allergens, as well as showing symptoms of allergy.  

When the germ-free mice were exposed to peanut allergens, they demonstrated a greater immune response than normal mice and also demonstrated features of an anaphylactic reaction.

The researchers found that adding Bacteroides to the gut of the germ-free mice had no effect on the allergic reaction. However, adding Clostridia bacteria reduced sensitivity to the peanut allergen, making their allergic response similar to normal mice.

This suggests that Clostridia plays a role in protecting against sensitisation to food allergens.

This was further confirmed when Clostridia was used to recolonise the guts of the antibiotics mice and was found to reduce their allergic response.

The researchers then carried out further laboratory experiments looking at the process by which Clostridia could be offering protection. They found the bacteria increases the immune defenses of the cells lining the gut.

One specific effect seen was how Clostridia increased the activity of a particular antibody, which reduced the amount of peanut allergen entering the bloodstream by making the gut lining less permeable (so substances are less likely to pass through it).

 

How did the researchers interpret the results?

The researchers concluded that they have identified a "bacterial community" that protects against sensitisation to allergens and have demonstrated the mechanisms by which these bacteria regulate the permeability of the gut lining to food allergens.

They suggest their findings support the development of new approaches for the prevention and treatment of food allergy by using probiotic therapies to modulate the composition of the gut bacteria, and so help induce tolerance to dietary allergens.

 

Conclusion

This research examined how normal populations of gut bacteria influence mouse susceptibility to peanut allergens. The findings suggest the Clostridia group of bacteria may have a particular role in altering the immune defenses of the gut lining and preventing some of the food allergen entering the bloodstream.

The findings inform the theory that our increasingly sterile environments and increased use of antibiotics could lead to a reduction in our normal gut bacteria, which could possibly lead to people developing a sensitivity to allergens.

But these findings are in the very early stages. So far, only mice have been studied, and only their reactions to peanuts. We don't know whether similar results would be seen with other tree nuts or other foods that can cause an allergic response.

Also, although this research provides a theory, we do not know whether this theory is correct. We don't know, for example, whether people with a peanut allergy do (or did) have reduced levels of certain gut bacteria populations and whether this contributed to the development of their allergy. We also do not know whether treatments that reintroduce these bacteria could help reduce the allergy.

As the researchers say, the study does open an avenue of further study into the possible development of probiotic treatments, but there is a long way to go. 

Professor Colin Hill, a microbiologist at University College Cork, was quoted by the BBC as saying: "It is a very exciting paper and puts this theory on a much sounder scientific basis."

But he does offer due caution, saying: "We have to be careful not to extrapolate too far from a single study, and we also have to bear in mind that germ-free mice are a long way from humans."

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Summary

"Bacteria which naturally live inside our digestive system can help prevent allergies and may become a source of treatment," BBC News reports after new research found evidence that Clostridia bacterium helps prevent peanut allergies in mice.

Links to Science

Gut bugs 'help prevent allergies'. BBC News, August 26 2014

Probiotics may help prevent peanut allergies, animal study shows. Fox News, August 26 2014

Useful Links

Further Readings

Stefka AT, Feehley T, Tripathi T, et al. Commensal bacteria protect against food allergen sensitization. PNAS. Published online August 25 2014

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