More possible causes of Asthma (Wake-Up America)

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Science Daily Magazine February 25, 2003

http://www.sciencedaily.com/releases/2003/02/030225065721.htm

Bacterial Infections Alter Allergic Response;

Findings Support Hygiene Hypothesis

Original Source: National Jewish Medical And Research Center

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 , 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. , 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, 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 again, and their allergic response was evaluated.

On several measures, the mice that had been infected showed a milder

reaction to the ovalbumin than did the control mice. Bronchial

hyperresponsiveness (a measure of the " twitchiness " of the airways of

these asthma-prone mice), levels of the cytokine IL-4, and total white

cell count in the airways were all lower in the previously infected mice

than in mice who were not infected. Levels of gamma interferon, which is

associated with a healthy non-allergic immune response, were higher in

the previously infected mice.

When mice were first sensitized and exposed to ovalbumin, then infected

with bacteria, they showed greater bronchial hyperresponsiveness and

airway inflammation than did control mice.

" Our results support the hygiene hypothesis, " said lead author Hong Wei

Chu, M.D. " Although mice are clearly different from humans, this kind of

data, generated in a controlled experiment, adds important new evidence

to help evaluate the hygiene hypothesis. "

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Note: This story has been adapted from a news release issued for

journalists and other members of the public. If you wish to quote from

any part of this story, please credit National Jewish Medical And

Research Center as the original source.

http://www.sciencedaily.com/releases/2003/02/030225065721.htm