Researchers at National Jewish Medical and Research Center have gathered strong experimental support for the hygiene hypothesis, a proposed explanation for the worldwide rise in asthma and allergies. The research team, led by Richard Martin, M.D., found that early infection with the bacterium Mycoplasma pneumoniae reduced a mouse's subsequent response to allergens. Alternatively, mice exposed to allergens prior to infection, developed a stronger allergic response. The research team is reporting its results in the March 2003 issue of the journal Infection and Immunity.

"For the first time, we have shown that a bacterial infection can modify the allergic response," said Dr. Martin, Vice Chair of the Department of Medicine at National Jewish. "Timing is everything, however. Our results suggest that M. pneumoniae, or a related pathogen, could help prevent asthma and other allergic diseases, but only if the infection occurs before a person is sensitized to an allergen."

Asthma and allergies have both been on the rise for several decades, especially in developed countries. The hygiene hypothesis has offered one explanation for this increase: compared with the past, children living in these countries today are exposed to fewer infectious organisms, which are necessary to properly train their developing immune systems. As a result, their immune systems overreact to relatively harmless irritants, leading to allergies and asthma.

So far, however, most evidence both for and against the hygiene hypothesis has been indirect and observational. The National Jewish research team sought more direct evidence using a mouse model of asthma and the bacterium M. pneumoniae, a common cause of community-acquired pneumonia.

In their study, Martin and his colleagues inoculated mice with either the bacterium or with a saline solution. Then all the mice were made allergic to the egg protein ovalbumin. Two weeks later, the mice were then exposed to the ovalbumin
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Contact: William Allstetter
allstetterw@njc.org
303-398-1002
National Jewish Medical and Research Center
25-Feb-2003

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