Dr Michael Holtzman, of the Washington University School of Medicine, said his research "will change the way people think about asthma".

His idea is that asthma is not caused by allergies, as many scientists believe, but by a faulty immune reaction in the cells lining the airways.

If confirmed, the finding could lead to new therapeutic approaches to deal with the disease.

Questioning the traditional view

Dr Holtzman's team published its findings in the Journal of Clinical Investigation.

The study focuses on the role played by epithelial cells, which line the airways into the lungs.

The traditional view of asthma holds that asthma is an allergic response, the researchers said.

In this model, an attack is caused by an allergen such as dust provoking a roving immune cell to react.

The immune cell then sends out chemical signals known as cytokines, attracting many more immune cells to the airways. This results in inflammation.

'Cells in the airway to blame'

But in Dr Holtzman's model, the static epithelial cells are to blame.

He performed research 20 years ago that suggested they perform a protective function, detecting foreign particles.

He said: "It seems that these cells are in fact specially programmed for host defence and are abnormally programmed in people with asthma."

He said many asthmatic patients do not suffer from allergies and that most patients with allergies do not develop asthma.

Immune response

His new research looked at a gene that triggers an immune response when it detects a virus.

It found that in asthma, this gene could operate even in the absence of a virus.

The researchers studied epithelial cells from healthy people, people with chronic bronchitis and people in asthma.

In the first two groups the protein that causes the gene to trigger a reaction was in a non-sensitive part of the cell, "presumably inactive".

But in 24 of the asthma patients, the protein was in the cell's nucleus, "presumably switching on genes".

Improvements for treatment

The team also considered how this finding will affect treatment.

Dr Holtzman and colleagues discovered that a virus that causes respiratory infections can prevent the guilty protein from activating genes.

They proposed that an aerosol of the virus - genetically altered so as not to damage immunity - could stop asthma