Immune System 'Killer' T-Cells May Not Be Key to Asthma

New study finding contradicts previous research, experts say.

By Serena Gordon
HealthDay Reporter
Wednesday, April 4, 2007; 12:00 AM

Copyright © 2007 ScoutNews, LLC. All rights reserved.

WEDNESDAY, April 4 (HealthDay News) -- While previous research suggested that a certain type of immune system cell -- called invariant natural killer T-cells -- might play a role in the development of asthma, a new study concludes that's just not the case.

In stark contrast to a previous study that found that these cells made up about 60 percent of the T-cells in an asthmatic's lungs, the current study found that fewer than 2 percent were invariant natural killer T-cells.

"We not only failed to find any evidence of raised counts of invariant natural killer T-cells in mild asthma and chronic obstructive pulmonary disorder but also failed to reproduce the observations [from past research] in moderate to severe disease," said one of the study's authors, Dr. Ratko Djukanovic, professor of respiratory medicine and director of Allergy and Inflammation Research at Southampton School of Medicine in the United Kingdom.

Djukanovic said he's not sure why this study found such low numbers of killer T-cells, but that improvements in the technology may have allowed his team to identify invariant natural killer T-cells with a higher degree of specificity.

Results of the study are published in the April 5 issue of the New England Journal of Medicine.

Asthma is a chronic lung disorder that causes symptoms such as wheezing, coughing and shortness of breath. About 20 million Americans have the lung disease and more than 4,000 people die of asthma complications each year, according to the U.S. Centers for Disease Control and Prevention.

Despite the disease's prevalence, the exact cause remains unknown. Health experts know that asthma can be triggered by a reaction to certain substances, such as dust mites, pollen or even cold air. It was commonly believed that exposure to allergens would cause the body to produce T-cells known as CD4+ helper T-cells, which would then release substances called cytokines that cause airway inflammation.

However, research published last year suggested that rather than the helper T-cells, it was actually killer T-cells at the root of this process in people with severe asthma.