Asthma war pinpoints cell target

By CHARLES ARTHUR

A type of white blood cell has been fingered as being directly responsible for the development of asthma.

The cells, called eosinophils, have often been identified in the lungs of people with asthma. Two separate American studies provide new evidence to show that eosinophils are closely involved in the disease.

By breeding mice without the cells, scientists showed that substances which triggered an asthmatic reaction in normal mice had no effect on the mice which lacked eosinophils - a finding that could be key in developing treatments for the condition in future.

The work, published in the journal Science, contradicts a study published in 2000 in the medical journal The Lancet, which concluded that eosinophils did not have a significant role in the development of asthma in humans.

The latest research will re-energise efforts to produce drugs that treat them.

Eosinophils are a type of white blood cell found in animals. Their natural role appears to be to protect against parasites, by congregating around them and releasing deadly toxins. In an asthma attack, those toxins are released inappropriately - leading to damage of the lung, nose and throat tissues.

"The new studies clearly show evidence that eosinophils have a role in asthma," said Dr Marsha Wills-Karp, chair of the division of immunobiology at Cincinnati Children's Hospital Medical Centre, who commented on the studies for Science. "If these cells turn out to be important, they will be good drug targets."

Eosinophils have for a long time been identified in the lungs of people with asthma, but scientists could not find evidence either way on whether they contributed to the condition.

In the first study, a Mayo Clinic team in Arizona found that eosinophils were essential for asthma to develop.

The second, separate study at Harvard Medical School in Boston, led by Alison Humbles, suggested that they were important in only one aspect of the disease - producing the long-term effects of asthma on lung structure, rather than being instrumental in triggering the initial attack.

Current thinking is that the role of eosinophils may depend on the person's genetic makeup, with different genes leading to varying importance.

"As there are likely many underlying causes of asthma, there may not be any one magic bullet for the treatment of asthma,"said Dr Wills-Karp.

"The wave of the future for asthma may be a pharmacogenetic approach in which you tailor drug therapies to individuals based on genetic factors. This approach is being taken in many areas of medicine."

- INDEPENDENT