New Clue to Development of Asthma

'Natural Killer' Cells May Be Involved, Study Shows

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March 15, 2006 -- A newly identified type of cell may be a leading suspect in how asthma develops, new research shows.

The cell type has a bulky name: CD4+ invariant natural killer T cells, or more simply natural killer T cells.

Those cells seem important in asthma's development, researchers report in The New England Journal of Medicine. The finding might lead to new asthma treatments and explain why current therapies, while helpful for many asthma patients, don't always work.

The researchers included Omid Akbari, PhD. Akbari works in the pediatrics department of Harvard Medical School and the immunology division of Children's Hospital Boston.

Cells Stood Out

T cells are tools of the immune system. Previously, asthma experts focused on a different, conventional type of T cell. Those T cells are close relatives of natural killer T cells.

In studying lung samples from 14 patients with moderate to severe asthma, Akbari's team found that 60% of the asthma patients' T cells were natural killer T cells, not conventional T cells.

The researchers found much lower levels of natural killer T cells in lung samples from six people with healthy lungs and five people with a disease called sarcoidosis, which mainly involves the lungs.

'Striking' Results

The natural killer T cells normally account for less than 1% of all CD4+ T cells in the blood, according to Akbari's study.

The high levels of those natural killer cells in asthma patients' lungs were a "striking" finding, the researchers write. "They can produce cytokines [inflammatory proteins] very rapidly and directly cause asthma," Akbari says in a news release.

Past research done on mice had also pointed toward a role for natural killer T cells in asthma, Akbari's team observes.

New Treatments?

Natural killer T cells are triggered by different chemicals than conventional T cells, note Akbari and colleagues. They say if their theory is right, it might be possible to develop new asthma treatments that target natural killer T cells in asthma patients' lungs.

Steroids used in asthma treatment affect conventional T cells and other inflammatory cells but seem to have little effect on natural killer T cells, says Akbari's colleague, Dale Umetsu, MD, PhD, in the news release.

"If we can specifically eliminate natural killer T cells, we should be able to treat asthma much more effectively," Umetsu says.


Second Opinion

The findings, if confirmed, could have "far-reaching consequences for patient care," states a journal editorial.

But more work is needed to confirm the theory, writes editorialist A. Barry Kay, MD, PhD. Kay works in London at Imperial College's National Heart and Lung Institute and wasn't involved in Akbari's study.

Sidelining natural killer T cells could have other consequences, Kay points out. It's not certain that natural killer T cells are specific to asthma and not other conditions involving airway inflammation, such as chronic obstructive pulmonary disease (COPD), Kay notes.

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SOURCES: Akbari, O. The New England Journal of Medicine, March 16, 2006; vol 354: pp 1117-1129. Kay, A. The New England Journal of Medicine, March 16, 2006; vol 354: pp 1186-1188. News release, Children's Hospital Boston.
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