Antibiotics alter GI tract microbes and increase lung sensitivity to allergens

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Antibiotics alter GI tract microbes and increase lung sensitivity to allergens

A 2004 study could help explain increasing rates of asthma, allergies and

inflammatory diseases. Data collected so far suggests that the real problem may

be connected to microbes in the gut.

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27 May 2004, 09:30 GMT - At the American Society for Microbiology meeting this

week, scientists from the University of Michigan Medical School presented

results of experiments with laboratory mice indicating that antibiotic-induced

changes in microbes in the gastrointestinal tract can affect how the immune

system responds to common allergens in the lungs.

" We all have a unique microbial fingerprint - a specific mix of bacteria and

fungi living in our stomach and intestines, " spokesman and lead investigator,

Huffnagle said. " Antibiotics knock out bacteria in the gut, allowing fungi

to take over temporarily until the bacteria grow back after the antibiotics are

stopped. Our research indicates that altering intestinal microflora this way can

lead to changes in the entire immune system, which may produce symptoms

elsewhere in the body. "

If confirmed in human clinical studies, Huffnagle believes his research findings

could help explain why cases of chronic inflammatory diseases, like asthma and

allergies, have been increasing rapidly over the last 40 years - a time period

that corresponds with widespread use of antibiotics.

To understand the implications of the U-M research, it's important to know

something about the complex relationship between the gastrointestinal,

respiratory and immune system in the human body.

Every time you inhale, air flows past mucus-producing cells and tiny hairs

designed to trap bits of pollen, dust and spores before they enter the lungs.

These trapped particles are swept into the stomach with saliva and mucus as you

swallow.

" Anything you inhale, you also swallow, " Huffnagle explained. " So the immune

cells in your GI tract are exposed directly to airborne allergens and

particulates. This triggers a response from immune cells in the GI tract to

generate regulatory T cells, which then travel through the bloodstream searching

the body for these antigens. These regulatory T cells block the development of

allergic T cell responses in the lungs and sinuses. "

Most of the time, in ways scientists don't completely understand, the GI tract

immune system modulates or dampens down the allergic T cells' response to

incoming allergens in the lungs, according to Huffnagle. Yet when antibiotics

reduce the bacterial population in the GI tract, the number of yeast and other

fungal organisms increases.

In previous studies, researchers have discovered that fungi secrete molecules

called oxylipins that can control the type and intensity of immune responses.

This suggests the intriguing possibility that fungal oxylipins in the GI tract

prevent the development of regulatory T cells for swallowed allergens. In the

absence of regulatory T cells from the GI tract, T cells in the lungs become

sensitized to the presence of ordinary mold spores, pollen or other allergens.

The result is a hyperactive immune response, which can produce allergy symptoms

or even asthma.

Source: Datamonitor Newswire