House Dust Ingredient Linked to Allergic Asthma: Study

THURSDAY, Oct. 18 (HealthDay News) -- A bacterial protein known as flagellin and found in house dust could make allergic reactions to common indoor allergens worse, according to a new study of both mice and people.

Researchers from the U.S. National Institute of Environmental Health Sciences (NIEHS) and Duke University found that flagellin can prime an allergic response and trigger allergic asthma. Cleaning can reduce the amount of house dust to prevent an allergy flare-up.

"Most people with asthma have allergic asthma, resulting largely from allergic responses to inhaled substances," the study's corresponding author, Donald Cook, an NIEHS scientist, said in an institute news release. "Although flagellin is not an allergen, it can boost allergic responses to true allergens."

In conducting the study, the researchers found that mice exposed to house dust that were able to respond to flagellin showed symptoms of allergic asthma, such as more mucous production and airway obstruction and inflammation. The researchers noted, however, that mice unable to detect flagellin had reduced levels of these symptoms.

The researchers also found that people with asthma have higher levels of antibodies against flagellin in their blood, which suggests a link between people's environment and allergic asthma.

"More work will be required to confirm our conclusions, but it's possible that cleaning can reduce the amount of house dust in general, and flagellated bacteria in particular, to reduce the incidence of allergic asthma," Cook said.

"More than 20 million Americans have asthma, with 4,000 deaths from the disease occurring each year," study co-author Dr. Darryl Zeldin, NIEHS scientific director, added in the news release. "All of these data suggest that flagellin in common house dust can promote allergic asthma by priming allergic responses to common indoor allergens."

The study was published online Oct. 14 in the journal Nature Medicine. Although it showed an association between flagellin and worsened allergic reactions, it did not prove a cause-and-effect relationship.