Investigating why asthma sufferers struggle with respiratory viruses

Date: Sep-10-2014A new study that compared people with and without asthma sheds light on why asthma

sufferers struggle to cope with respiratory viruses like flu and the common

cold.

Writing in the Journal of Allergy and Clinical Immunology, the team behind the

investigation, from the School of Medicine at Washington University in St. Louis (WUSTL), MO,

concludes that a fundamental antiviral defense mechanism is intact in people with asthma, so

the reason they struggle with respiratory viruses must lie elsewhere in the immune system.

Asthma is a chronic disease that affects the airways in the lungs. These become inflamed

and make breathing difficult during an asthma attack. We don't know for sure what causes

asthma, except we know it can be triggered by allergens like pollen and dust mites, exercise,

hazards at work, tobacco smoke, air pollution and airway infections.

Researchers investigated interferon production and effectiveness in asthma

One view among researchers is that people with asthma do not produce interferons properly.

These defensive proteins - which "interfere" with invading viruses - are released by cells

lining the airways when they detect the incoming pathogens.

But when the WUSTL team compared interferon production in people with and without asthma,

they could find no evidence of this, as senior author Michael J. Holtzman, Selma and Herman

Seldin Professor of Medicine at WUSTL, explains:

"One school of thought says there is a defect in interferon production - that patients with

asthma don't produce enough interferon. But we couldn't find any significant differences

between the two groups. In fact, we were struck by how similar they were."

For their study, Prof. Holtzman and the team investigated the interferon response to

influenza A virus and respiratory syncytial virus (RSV) - two common airway viruses.

In 2009, nearly 3,388 Americans died from asthma, which is a rate of about 9 deaths a day.

They took samples of airway cells from 11 patients with mild to severe asthma and seven

control patients without asthma, and tested their interferon response to the two viruses.

While this is not a large number of patients, the team carried out a detailed analysis,

taking into account events further down the line that might be triggered by a release of

interferon.

They looked not only at the amount of interferon produced, which was similar in both

groups, but they also looked for possible differences in its effectiveness. For example, how

well did the released interferon trigger the downstream events necessary for fighting the

viruses?

To try and answer this question, they compared the genes activated by interferon in the two

groups.

Prof. Holtzman says "the products of these genes are very effective in their antiviral

action. So it's a battlefield. Who will win out? The interferon-stimulated genes or the viral

genes?"

Interferon production was similar in asthmatic and non-asthmatic patients

But even in this part of the defense process triggered by interferon release, the asthmatic

patients and the non-asthmatic patients showed very similar results. One way to check the

progress of the battle against a virus is to measure the amount of virus inside cells. But

this was the about the same for the two groups at various points of time during the study.

Prof. Holtzman concludes:

"Whatever is causing asthmatics and non-asthmatics to experience differences in how well

they recover from these respiratory infections - why patients with asthma are more likely to

end up in the hospital, for example - this interferon mechanism is not the deciding factor

based on what we've seen so far."

The immune system is highly complex, and the team continues to look for other potential

culprits. They are doing more studies with larger groups. One idea they are pursuing is that

viruses may have a mechanism for inducing inflammatory airway disease that people with asthma

and related lung disorders like chronic obstructive pulmonary disease (COPD) are susceptible

to.

Meanwhile, in August 2014, Medical News Today learned of a study conducted in mice

that found stress in pregnancy is linked to

offspring's asthma risk.

According to the Centers for Disease Control and Prevention (CDC),

about 1 in 12 adult Americans has asthma, and about 1 in 11 children, and the disease costs

the US economy about $56 billion a year. In 2009, nearly 3,388 Americans died from asthma,

which is a rate of about 9 deaths a day.

Written by Catharine Paddock PhD

View all articles written by Catharine, or follow her on:

Courtesy: Medical News Today Note: Any medical information available in this news section is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.