Patients treated with the antibody, which is grown in a laboratory, performed better in lung tests.

The researchers say the treatment offers a new approach to managing the disease, as it would require an injection once every two to four weeks.

Asthma is caused by inflammation in the lungs.

This inflammation is partly caused by a type of immune cell called the eosinophil.

Asthma sufferers have lots of these cells, which are activated by chemical signals, in their airways.

Antibodies attack cells

Normally patients with severe asthma take steroids to prevent inflammation.

But the drugs cannot control the disease in all patients.

Researchers writing in The Lancet say they can reduce the inflammation by disabling part of the immune system.

The antibody is produced in a laboratory

They achieve this by destroying the cells that carry the chemical signal, called CD4 T lymphocytes.

They injected asthma patients with the antibodies and found that there were significantly fewer CD4 T lymphocytes.

Patients who took the antibody showed improved performance in a test called peak expiratory flow measurement, which measures the speed at which air is exhaled.

The team were investigating the relationship between the T cells of the immune system and asthma.

An accidental discovery

Dr Neil Barnes, of the department of respiratory medicine at the London Chest Hospital, worked on the study.

He that the study involved 22 patients with the most severe asthma.

"These are the people who are on all the conventional treatments and they are still wheezy and short of breath," he said.

The benefits of the treatment were uncovered accidentally, Dr Barnes said.

He explained that the study had set out to establish simply whether or not the introduction of antibodies generated any side-effects.

"But as an add-on to that we did these very careful measurements to see if it could show an improvement in their asthma," he said.

They found that patients with the highest dose of the antibody showed a "marked improvement in lung function".

Once scientists understand exactly how T cells affect asthma they might be able to develop similar treatments for sufferers with milder forms of the disease, Dr Barnes added.

Growing trend in asthma research

The National Asthma Campaign said that study was part of a growing trend towards investigating vaccines for asthma.

"It is possible that vaccinations of whatever sort may well be the way forward for treating asthma," a spokeswoman said.

Although it was impossible to tell how many of the UK's 3.4 million asthma sufferers would benefit from this particular piece of research, it was still an interesting development.

"Any potential breakthrough or new treatment is something we always welcome," she added.

The antibody is developed first in animals and then combined with human material.

Copies of it are grown in a laboratory and this is what is injected.