'Natural Killer T Cell' Level Found in Lungs of Patients Is Far Higher Than in Others
By JENNIFER LEVITZ
March 16, 2006; Page D6
Scientists have identified a new type of immune cell in the lungs of asthma patients, a finding that could change the understanding of what triggers the disease and open new avenues of treatment.
A study being published today in the New England Journal of Medicine found that asthma patients' lungs had a high level of "natural killer T" cells -- which are part of the body's immune system -- while healthier people and those suffering from other respiratory ailments had almost none. A normal level of such cells is benign, yet too many can lead to tissue inflammation.
It had been thought that a different kind of immune cell was the main culprit in asthma. Those cells, called "helper T cells," can make asthma patients sensitive to proteins such as dust mites or pollen.
The natural killer cells, on the other hand, are sensitive to a different irritant -- lipid, which is essentially fat that is found in the body and in some plants and food. Practically, the findings mean doctors may have found new triggers for asthma.
"Everyone for 50 years was looking at proteins," said Dale T. Umetsu, an immunologist at Children's Hospital in Boston and Harvard Medical School, who conducted the study with researchers from Stanford University, Karolinska Institute in Stockholm and the La Jolla Institute for Allergy and Immunology in San Diego.
Natural killer T cells are a normal component of the immune system, fighting infections, and in instances, preventing some autoimmune diseases. Trouble occurs if a person develops too many of the cells or if the cells get activated inappropriately, releasing inflammatory agents that can lead to such illnesses as colitis or heart disease. They aren't usually found in the lungs.
The study examined the bronchial fluid of 44 adult patients, 14 of whom had moderate to severe asthma with frequent wheezing, coughing and shortness of breath. Six other patients were healthy, while five others had sarcoidosis, a different type of respiratory inflammatory disease. The doctors found, as expected, that the lungs of asthma patients and those with sarcoidosis had a high level of helper cells.
But the surprise, Dr. Umetsu said, came when the researchers examined the bronchial fluid for natural killer T cells -- and discovered 63% of the cells found in asthma patients were killer T cells. By contrast, less than 1% of the cells in the fluid from either controls or patients with sarcoidosis were of that type. Dr. Umetsu called the findings "striking" and said they could lead to research for treatments targeting the killer T cells.
The study comes several months after another in the Journal of Immunology found killer T cells in the blood of asthma patients -- while the latest one looked at the lungs. An editorial by A. Barry Kay, of the National Heart and Lung Institute in London, in the Journal of Medicine said the two studies have "far-reaching consequences for patient care" but said more research was needed to determine whether the prominence of natural killer T cells in the airway causes the asthma or is the result of it.
Mike Tringale, a spokesman for the Asthma and Allergy Foundation of America, a nonprofit group in Washington, said yesterday, "a better understanding of the triggers will lead to a better understanding of the disease."
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