"We revealed a link between dust from farms and protection against asthma and allergies," explains Bart Lambrecht, study co-author and researcher at the University of Ghent (Belgium). To do this, the scientists exposed mice to dust from farms from Germany and Switzerland.
The experiments carried out confirmed that the mice were fully protected from allergy to dust mites, "the most common cause of allergy in humans", Lambrecht declares.
The protection of the children from allergies was produced by regular exposure to bacterial particles and farm dust, as their inflammatory immune responses were blunted. According to scientists, farm dust causes the mucous membrane inside the respiratory tract to react less severely to allergens such as dust mites.
As the cause of this protective effect, the work involves a particular anti-inflammatory enzyme, A20. “The body produces this protein when it comes in contact with farm dust. If A20 is inactivated in the mucous membrane of the lungs, the dust is no longer capable of reducing the allergic or asthmatic reaction ”, specifies Hamida Hammad, co-author and scientist at the same center as Lambrecht.
For this reason, households with pets, as well as dairy farms - where children breathe dust with high doses of fungal particles, bacteria from stables or endotoxins, that is, toxins present in the external membranes of some bacteria -, prevent allergies, although how is still unknown.
Experiment in mice
Now, the authors of this work have shed light on this mystery. The researchers subjected mice to endotoxins every other day for two weeks. They were then exposed to allergy-causing dust mites in the home, which often cause asthma in humans.
Thus, they found that mice that had been regularly subjected to endotoxins did not develop allergic manifestations, while control mice did.
For the scientists, “it appears that endotoxin exposure protected mice by stopping the ability of animal lung epithelial cells to generate pro-inflammatory molecules, despite the fact that this protective effect only worked in the presence of a good copy of the enzyme A20 ".
Towards a future vaccine
In order to confirm the presence of A20 in this protective effect, the researchers resorted to the use of lung biopsy samples from healthy adults and asthmatics.
After regular exposure to endotoxin, cells from healthy humans generated fewer inflammatory molecules characteristic of allergies than their asthmatic counterparts, in which A20 levels were also lower.
“We also evaluated a group of 2,000 children who were being raised on farms and found that most of them were protected. Those who were not and continued to develop allergies actually had a genetic variant of the A20 gene that caused a failure in the A20 protein, ”Lambrecht emphasizes.
Scientists are currently trying to identify the active substance in farm dust responsible for providing that protection. Once it is identified, the development of a preventive medicine against asthma will be the next step.
“Finding out how dust provides this type of protection will lead us towards the development of a vaccine against asthma and new therapies to prevent allergies. However, we still need several years of research before these advances reach patients, ”concludes Hammad.