Rare Immune System Cell Could Be Primary Asthma Trigger
The lungs of asthma patients contain high levels of a rare immune system cell that can cause tissue inflammation, according to a study published on Thursday in the New England Journal of Medicine "that could change the understanding of what triggers [asthma] and open new avenues of treatment," the Boston Globe reports (Allen, Boston Globe, 3/16).
Traditionally, scientists have thought that the immune system's "helper T cells," which make asthma patients sensitive to proteins such as dust mites or pollen, were the primary cause of asthma. However, in the latest study, researchers found that "natural killer T cells," another component of the immune system, might actually be the primary cause.
Natural killer T cells help fight infection and prevent some autoimmune diseases. Individuals who have too many natural killer T cells develop inflammation, which can cause such illnesses as colitis or heart disease. The cells normally are not found in the lungs.
For the study, researchers from Children's Hospital Boston, Stanford University, the Karolinska Institute in Sweden and the La Jolla Institute for Allergy and Immunology in San Diego examined the bronchial fluid of 44 adults, 14 of whom had moderate to severe asthma with frequent wheezing, coughing and shortness of breath. Six other participants were healthy, and five had sarcoidosis, a different kind of respiratory inflammatory disease.
The researchers found that participants with sarcoidosis and asthma had high levels of helper cells in their bronchial fluid, as expected. However, they also found that 63% of the cells in the bronchial fluid of asthma patients were natural killer T cells, compared with less than 1% of the cells in the bronchial fluid of the healthy people or those with sarcoidosis (Levitz, Wall Street Journal, 3/16).
According to the Globe, the researchers said the traditional belief that helper T cells were the cause of inflammation in people with asthma could have been the result of a case of "mistaken identity," because helper T cells can look very similar to natural killer T cells under a microscope (Boston Globe, 3/16).
Study co-author Dale Umetsu, an immunologist at Children's Hospital Boston and Harvard Medical School, called the findings "striking" and said they could lead to research for treatments targeting the natural killer T cells (Wall Street Journal, 3/16). "Conventional type 2 helper cells may not be as important in causing asthma as we thought," Umetsu said, adding, "We now believe that natural killer T cells may be equally or more important. ... Clearly, what we are proposing is a very new paradigm for asthma."
Umetsu noted that his laboratory is researching treatments that expel natural killer T cells from the lungs or eliminate the cells' ability to cause inflammation by summoning other immune cells (Boston Globe, 3/16).
In an accompanying editorial, Barry Kay of the National Heart and Lung Institute in London said the new study -- combined with a separate study published recently in the Journal of Immunology that found natural killer T cells in the blood of asthma patients -- has "far-reaching consequences for patient care." However, he added that more research is necessary to determine whether high levels of natural killer T cells in the airway cause asthma or are the result of it (Wall Street Journal, 3/16).
The NEJM study is available online.