Flu discovery could cut asthma risk

Asthmatic children who contract flu frequently end up in hospital fighting for breath. But the reason for the severity of asthma attacks brought on by flu and other infections has not been clear.

A mouse study in the US has now pointed to an explanation. Scientists believe the trigger mechanism involves natural helper cells, a recently discovered element of the immune system.

Natural helper cells were first found in the gut, where they protect against parasitic worm infections.

Lead researcher Dr Dale Umetsu, from the Children’s Hospital Boston, said: “Since the lung is related to the gut – both are exposed to the environment – we asked if natural helper cells might also be in the lung and be important in asthma.”

Tests showed that the cells did exist in the lungs of asthmatic mice with influenza.

The virus stimulated production of an immune system signalling molecule that activated natural helper cells. These in turn secreted chemicals that triggered asthma attacks.

“Without these cells being activated, infection did not cause airway hyper-reactivity, the cardinal feature of asthma,” said Dr Umetsu.

The research is reported in the journal Nature Immunology.

Two other asthma pathways involving different immune system components are already known. Natural helper cells appear to provide a third, said Dr Umetsu.

He added: “We need to understand the specific asthma pathways present in each individual with asthma and when they are triggered, so we can give the right treatment at the right time.”