To the village, to Grandpa!
Scientists have found a new explanation for the harm of hygiene to immunity
Belgian scientists have found out why children who grew up in the village suffer less from asthma and some types of allergies than urban children: bacteria living in the air on the farm cause an inflammatory reaction in the lung tissues, which subsequently protects these organs from asthma. The experiments served as a new proof of the hypothesis about the harm of hygiene (first of all, cleaning the air and surfaces in residential premises) for the human immune system. The results of the study are presented in the journal Science: Schuijs et al., Farm dust and endotoxin protect against allergy through A20 induction in lung epithelial cells (the results of the work are briefly described in the press release of Vrije Universiteit Brussel Growing up on a farm provides protection against asthma and allergies - VM).
It has long been known that those who spent their early childhood in the village are much less likely to suffer from allergies and asthma. Some scientists believe that the reason for this resistance is the abundance of endotoxins (elements of the cell membrane of gram-negative microorganisms that enter the environment after their death) in the village air.
To test the fact of the protective effect of endotoxins (which are also called lipopolysaccharides), Belgian researchers conducted an experiment on mice. For two weeks, they injected these molecules into the sinuses of rodents aged from six months to a year. The mice were then forced to inhale air with a high content of dust mites. Animals treated with endotoxins proved invulnerable to asthma, while rodents from the control group demonstrated a powerful allergic reaction, and also became ill with asthma.
In contact with ticks, endotoxin–hardened lung epithelial cells produced significantly fewer anti-inflammatory cytokines and dendritic cells associated with the latter, an important tool of the immune system. It also turned out that the A20 enzyme plays a key role here. Mice deprived of the ability to produce this enzyme, endotoxins could not protect against asthma.
Similar results were obtained when mice were injected not with endotoxins, but with dust and litter from farms containing not only lipopolysaccharides, but also other fragments of bacteria, fungi and plants. Finally, among 500 village children examined by scientists, allergies and asthma were five times more common in those in whose body the activity of the A20 enzyme was reduced (due to gene mutations).
Previously, proponents of the hypothesis about the harm of hygiene believed that the state of the air directly affects the cytotoxic T-lymphocytes of the immune system. Now it has become clear that endotoxins "affect what is happening in the lung cells. Contact with the natural environment at an early age allows you to "cool" the epithelium – so that it learns to distinguish dangerous molecules from harmless ones," says the head of the study, pulmonologist Bart Lambrecht.
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04.09.2015