THURSDAY, Sept. 16, 2004 (HealthDayNews) -- A long-suspected link between asthma and white blood cells called eosinophils has been confirmed by two separate studies in genetically tailored mice.
The findings could lead to new ways of treating asthma, said James J. Lee, a leader of one of the studies.
"We identified eosinophils as a potential cause of asthma, but what those cells are actually doing will be the subject of research for the next few years," said Lee, who is associate professor of biochemistry and molecular biology at the Mayo Clinic in Scottsdale, Ariz.
But at least the studies clarified "an argument that has been going back and forth over the last hundred years whether they are actual causative agents," Lee said. "Finding proof they actual did it has been out of everyone's grasp."
Both studies appear in the Sept. 17 issue of Science.
Eosinophils are a part of the immune defense system. Many decades ago, they were shown to be present in airways affected by asthma, which led to the belief that they were at least partly responsible for the inflammation and breathing difficulties caused by the disease. The Mayo Clinic group has spent the last eight years trying to prove that point, Lee said.
They succeeded by producing a strain of mice that were genetically altered to have no eosinophils. When asthma attacks were provoked in the mice, the animals did not have the abnormal sensitivity of their airways and overproduction of mucus found with asthma. That's a direct indication the cells are involved in the disease, the researchers said.
The second experiment, led by researchers at Harvard Medical School, involved a different strain of mice bred to have no eosinophils and produced significantly different results. When asthma attacks were induced, these mice did have abnormal sensitivity of the airways and excessive mucus production. But they did not have the structural changes, such as an increase of airway smooth muscles, found in asthma, the study found.
One important value of the two studies is that they contradict a British study done in 2000, in which therapy aimed at eliminating eosinophil activity in human asthma patients was reported to be ineffective, said Marsha Wills-Karp. She is chairwoman of the division of immunobiology at Cincinnati Children's Hospital Medical Center, and co-author of an accompanying commentary in the journal.
That earlier report discouraged researchers from pursuing the eosinophil-asthma connection, but the two new studies "reopen the possibility of treating asthma by targeting eosinophils," Wills-Karp said.
However, the differing results of the two studies indicate that eosinophils might be a difficult target to hit in human asthma, she added. The fact that different results were reported for mice with different genetic makeups indicates that any therapy might give results that would vary because of genetic differences in patients, she explained.
"In certain individuals, eosinophils might play a major role," she said. "In others, they might not."
And the way that eosinophils might be targeted remains unclear, Lee said.
"We might not target eosinophils themselves, but one or more of their activities," he said.
An estimated 17 million people in the United States have asthma. The disease is responsible for nearly half a million hospital stays each year, and its treatment costs billions of dollars annually, according to the Asthma and Allergy Foundation of America.
More information
The National Library of Medicine offers a guide to asthma.
