Scientists explain why farm children less likely to have asthma

A European team on Thursday proposed a new explanation for why children growing up on farms are far better protected against asthma and allergies.

The protective effect may be created by a particular anti-inflammatory protein called A20, which the body produces upon contact with farm dust, according to the team, led by researchers from Belgium's Flanders Institute for Biotechnology (VIB) and Ghent University.

The findings, published in the leading journal Science, may represent a major step forward towards the development of an asthma vaccine.

For the study, the researchers first exposed mice to farm dust extract, a bacterial component called endotoxin, every other day for two weeks.

They then presented these mice with allergy-driving house dust mites, which often cause asthma in people, finding that mice that had been regularly exposed to endotoxin did not develop allergic features, while control mice did.

Further research found that endotoxin exposure appears to have protected the mice by squashing the ability of the animals'lung epithelial cells to generate pro-inflammatory molecules, but this protective effect only worked in the presence of the A20 protein.

"When we inactivate the A20 protein in the mucous membrane of the lungs, farm dust is no longer able to reduce an allergic or asthmatic reaction," study author Professor Hamida Hammad of VIB and Ghent University said.

These findings were then tested in patients. The results showed that people suffering from allergies and asthma have a deficiency in the protective protein A20, explaining why they react to allergens so severely.

"Discovering how farm dust provides this type of protection has certainly put us on the right track towards developing an asthma vaccine and new allergy therapies," Hammad said. "However, several years of research are required still before they will be available to patients."

Some experts cautioned that the newly uncovered mechanism does not entirely explain the protective effect of farm life.

For example, it is commonly known that drinking raw cow's milk can provide protection against allergies, but that effect is unlikely to involve the lung epithelium, Gary Huffnagle of the University of Michigan, Ann Arbor, told Science.