NK cells

[Guest guest]

Immune System Cells May Be Cause of Asthma

By Serena Gordon

HealthDay Reporter

WEDNESDAY, March 15 (HealthDay News) -- As medical technologies improve,

researchers are rooting out more information about possible causes of common

diseases, such as asthma.

One new finding, reported in the March 16 issue of the New England Journal of

Medicine, is that immune system cells long thought to cause asthma may not be

the primary culprit behind the disease.

" We found that asthma is caused not by T-helper 2 cells as has been previously

thought, but by a novel class of cells called natural killer T cells, " said one

of the study's authors, Dr. Dale Umetsu, a professor of pediatrics at Harvard

Medical School and Children's Hospital Boston, and a visiting professor at

Stanford University in California.

" The majority of T cells in people with asthma aren't what we thought they

were, " he added.

According to Umetsu, natural killer T cells were only recently discovered

because the technology to differentiate these cells from others hasn't been

around long.

T cells are a part of the body's immune defenses and normally help rid the body

of foreign invaders, such as viruses or bacteria. In asthma, however, the immune

cells don't work as they should and instead produce inflammation in the lungs.

More than 20 million Americans have been diagnosed with asthma, according to the

U.S. Centers for Disease Control and Prevention, and about 4,200 people die from

the disease each year.

Asthma symptoms include wheezing, coughing, breathing difficulties and a feeling

of tightness in the chest. While the exact cause of the disease is unknown,

doctors do know that asthma can be exacerbated by exposure to certain triggers,

such as dust mites, pollen, pets and even exercise or cold air. There is no cure

for asthma, only treatments aimed at managing it.

Because studies in mice uncovered the presence of natural killer T cells only in

rodents with asthma, the researchers behind the new study compared samples from

14 people with asthma to samples from six healthy " controls " and five people

with another inflammatory lung disorder called sarcoidosis, which is unrelated

to asthma.

About 60 percent of the T cells in the asthma group were natural killer T cells,

not the expected helper T cells. No natural killer T cells were evident in

samples from the healthy control group or the people with sarcoidosis.

" These were very surprising findings -- a turn of events that no one suspected

in the past, " said Umetsu. " Part of the reason they escaped notice is they have

many features that are similar to T helper 2 cells. Now, we need to know more

about the biology of natural killer T cells to develop more specific therapies

for asthma. "

" None of the current [asthma] therapies are focused on targeting natural killer

T cells. Perhaps as we develop therapies that can eliminate them from the lungs,

we could have more effective and possibly curative therapies for asthma, " he

said.

The first step, however, is to confirm these findings in a larger group of

people, and in a more diverse population of people with asthma, because there

are different types of asthma. Some people have asthma that's triggered by

allergens, while for others exercise or cold air can induce airway spasms.

Also, Umetsu said that researchers have to learn more about how these cells work

and what causes them to go to the lungs initially. Natural killer T cells appear

to respond to different things than helper T cells.

Any potential therapy would have to specifically target the lungs because

natural killer T cells do have some protective effects in the rest of the body,

he added.

Dr. Field, director of the allergy and asthma clinic at New York

University Medical Center/Bellevue in New York City, said, " This may be a new

paradigm of how people develop asthma. "

But, he cautioned that more needs to be learned about these cells, such as

whether they are the actual cause of disease or if they simply appear in

response to the disease.

" You have to wonder which [immune cells] actually are causing the most

pathology, " Field said. " Are natural killer T cells causing the changes? Which

cell is the conductor and which is the actual locomotive? "