Could Asthma Be a Viral Affair?
Previous infection linked to breathing disorder
By Adam Marcus
MONDAY, Feb. 5 (HealthScout) -- Some asthma may be the result of an early viral infection that scrambles the genes of lung cells and makes them overly sensitive to irritants, new research suggests.
St. Louis scientists say mice with bronchitis and people with asthma both express an immune chemical linked to the airway inflammation. This molecule could offer doctors a new target for drugs to quell the breathing disorder, the scientists say.
A growing number of Americans -- now estimated at 17 million -- suffer from asthma, now the country's most common illness, according to the Asthma and Allergy Foundation. People with asthma develop inflamed and temporarily narrowed airways, making breathing difficult. The latest discovery hinges on a protein called IL-12 p40 -- or, rather, a double shot of that molecule known as p80.
Earlier studies suggested that p80 was an immune protein that floated around looking for an inflammatory fight to pick. But in the latest study, Dr. Michael Walter and his colleagues at the Washington University School of Medicine found that airway cells in mice infected with respiratory viruses churned out large amounts of the molecule.
The researchers looked at a type of lung tissue called barrier epithelial cells, which act as a harbor for viruses -- making them the port of entry for lung infections.
About two-thirds of the asthma patients they tested had higher-than-normal levels of p80, even though they didn't have signs of a current viral infection, the study says.
"The pattern of expression is the same in virus infection and asthmatic patients," Walter says. Details appear in today's issue of the Journal of Experimental Medicine.
Why that's true isn't clear, Walter says, but he has a couple of theories. Some asthma, he says, may be the result of an early viral infection that leads to the over-expression of p80, which in turn makes the lungs act as if they're continually fighting off viruses.
Or, he says, "it may be that a susceptible individual gets a viral infection and that sets off airway inflammation that can trigger asthma" -- in which case p80 is merely a marker for the reaction. "Right now, it's just an association that this happens in a viral infection and in asthmatics," Walter says. If p80 is truly the chemical spark that sets off asthma, he says, then dousing it with drugs might help prevent attacks. The researchers currently are exploring such a treatment, he says.
Dr. Sanjiv Sur, an immunologist and asthma expert at the University of Texas Medical Branch at Galveston, calls the St. Louis research "an interesting twist."
Sur and his colleagues recently found a bacterial molecule that they say can "profoundly augment" anti-viral proteins and prevent asthma in animals. The drug also appears to have vaccine-like effects on long-term control of the ailment, Sur says.
Even so, he says, the new findings suggest the need for caution in applying the experimental therapy. "Perhaps we should not rush in and start using immune enhancers because, at least under certain situations, they can play a role in making things worse," Sur says.
You also might want to read previous HealthScout articles on asthma.
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