Our lungs were long considered to be germfree and sterile. It was only recently discovered that, like our intestines and skin, our respiratory organs are colonised by bacteria. Now, tests conducted on mice by researchers working with Benjamin Marsland at the University Hospital in Lausanne have shown that these lung microbes offer protection against allergic asthma (*).
The researchers exposed the mice to an extract obtained from house dust mites. Neonates had a much stronger allergic reaction to the extract than older mice. Why? The lungs in newborn mice have not yet been colonised by the microbes that alter the immune system and make its responses less prone to allergic reactions.
Two-week adaptation process
The researchers have discovered that the process of colonisation and adaptation takes place during the first two weeks of the mouse's life. Young mice that were kept completely germ-free remained susceptible to asthma and had excessive immune responses to dust mite allergens even later in life.
Marsland and his team have already started studying whether lung microbes ensure healthy airways in humans as well. Pilot studies involving newborn babies in Switzerland and New Zealand indicate that the situation may be similar for men and mice. Further studies are required, however, to identify the potential mechanisms in humans.
Focus on newborns
"There would appear to be a developmental window early in life that determines whether or not an individual will develop asthma later," Marsland says. Until now, scientists and doctors have focused on asthma essentially from the point of view of the course of the disease and possible direct triggers. "We should probably focus on a much earlier stage, that of newborns."
What Marsland wants to know now is how big the developmental window is for building up the immune system in childhood. He hopes that the new discovery will help prevent asthma. Perhaps by encouraging pregnant women to eat more fruit and vegetables - quite recently Marsland showed that the dietary fibre contained in these foodstuffs also protects against allergic asthma by altering the microbial flora. That protection might be passed on to newborn babies.
(*) Eva Gollwitzer, Sejal Saglani, Aurélien Trompette, Koshika Yadava, Rebekah Sherburn, Kathy McCoy, Laurent Nicod, Clare Lloyd & Benjamin Marsland (2014). Lung microbiota promotes tolerance to allergens in neonates via PD-L1. Nature Medicine online. doi:10.1038/nm.3568
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Prof Benjamin J. Marsland
Lausanne University Hospital (CHUV)
Phone +41 21 314 13 78