House dust protein worsens allergic asthma symptoms

Oct 19 2012

By Helen Albert, Senior medwireNews Reporter

A bacterial protein found in common house dust may worsen a person's asthmatic response to other indoor allergens, say researchers.

The team screened house dust extracts to assess which microbial components were the most allergenic. They found that the bacterial protein flagellin stimulated strong allergic responses to inhaled egg white (ovalbumin) protein in a mouse model of airway inflammation.

Mice challenged with ovalbumin alone or flagellin alone did not become sensitized to ovalbumin and did not exhibit an allergic airway response to a subsequent repeat challenges.

They also found that the flagellin receptor, toll-like receptor 5, was required for strong allergic responses to be initiated to common indoor allergens such as dust mites, cockroaches, and animal dander in house dust.

"Most people with asthma have allergic asthma, resulting largely from allergic responses to inhaled substances," said investigator and author of the study published in Nature Medicine Donald Cook (National Institutes of Health [NIH], North Carolina, USA) in a press statement.

"Although flagellin is not an allergen, it can boost allergic responses to true allergens," he explained.

The researchers compared serum samples from people with and without asthma and found significantly higher levels of flagellin-specific antibodies in asthmatic compared with nonasthmatic individuals.

Bacterial products are known to act as adjuvants and are thought to promote asthma by initiating allergic sensitization to inhaled allergens, write the authors, and these results support this theory.

"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," said Cook.

"All of these data suggest that flagellin in common house dust can promote allergic asthma by priming allergic responses to common indoor allergens," commented study co-author Darryl Zeldin, also from the NIH.

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