[Shadow_Group] Fw: Antibiotics alter GI tract microbes, increase lung sensitivity to

[Shadow Spook]

Antibiotics alter GI tract microbes, increase lung sensitivity to
allergens


Posted on Wednesday, May 26, 2004 @ 8:20 AM PDT
Topic: Bio and Medicine



Allergies making your life miserable? Tired of popping antihistamines
like candy? Can't go anywhere without your inhaler? The real problem
may not be your stuffed-up head. It could be the microbes in your gut.
At the American Society for Microbiology meeting held here this week,
scientists from the University of Michigan Medical School will present
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.
http://www.scienceblog.com/community/modules.php?name==News&file==article&sid='74<http://www.scienceblog.com/community/modules.php?name==News&file==article&sid='74>
        


>From the University of Michigan Health System :

Antibiotics alter GI tract microbes and increase lung sensitivity to
allergens

Study could help explain increasing rates of asthma, allergies and
inflammatory diseases

Allergies making your life miserable? Tired of popping antihistamines
like candy? Can't go anywhere without your inhaler? The real problem
may not be your stuffed-up head. It could be the microbes in your gut.

At the American Society for Microbiology meeting held here this week,
scientists from the University of Michigan Medical School will present
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,'' says Gary
B. Huffnagle, Ph.D., an associate professor of internal medicine and
of microbiology and immunology in the U-M Medical School.
''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 says. ''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.
But when antibiotics reduce the bacterial population in the GI tract,
the number of yeast and other fungal organisms increases.

In previous studies, researchers in Huffnagle's lab discovered that
fungi secrete molecules called oxylipins, which can control the type
and intensity of immune responses. Huffnagle says 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.

To test Huffnagle's hypothesis, Mairi C. Noverr, Ph.D., a U-M research
fellow in internal medicine, gave a five-day course of oral
antibiotics to normal lab mice followed by a single oral introduction
of the yeast, Candida albicans, to create a consistent, reproducible
colony of microbes in the stomach and intestines. C. albicans is
normally found in the GI tract, and increased growth of C. albicans in
the gut is a common side-effect of antibiotics.

Two days after stopping the antibiotics - at a time when the gut
bacteria were growing back - Noverr exposed the mice to a common mold
allergen called Aspergillus fumigatus by inoculating spores into the
nasal cavities of all the mice in her study. She then examined the
mice for the presence of an allergic response in the airways and
compared results between the mice that received antibiotics and those
that did not.

''Mice treated with antibiotics and colonized with C. albicans showed
increased pulmonary hypersensitivity to A. fumigatus compared with
mice that didn't receive antibiotics,'' Noverr says. ''The
inflammatory response grew stronger with every exposure to the allergen.''

''After antibiotics changed the mix of microbes in the GI tract, the
mice developed an allergic response in the lungs when exposed to
common mold spores,'' Huffnagle explains. ''Mice that didn't receive
the antibiotics were able to fight off the mold spores.''

Huffnagle and Noverr will discuss details of the experiment in a
symposia lecture and poster presentation at the ASM meeting. Complete
data from the study has been submitted for publication in a future
issue of Infection and Immunity.

Huffnagle maintains that disruptions in the growth of bacteria and
fungi in the GI tract somehow interfere with the ability of regulatory
T cells to dampen the immune response to respiratory allergens. In
future research, he hopes to determine exactly how gastrointestinal
microbes are involved in the process of immune system modulation.

''We know from laboratory experiments that dietary antioxidants called
polyphenols, which are found in fruits and vegetables, can limit
fungal growth and that a diet high in saturated fats and sugars slows
the recovery of normal gut microflora,'' Huffnagle adds. ''The
Mediterranean diet is rich in sources of polyphenols, so it's
intriguing that Mediterranean-diet countries have lower rates of
allergies, asthma and other inflammatory diseases than Western-diet
countries like the United States, Canada and England.

''If we can determine exactly how microflora in the GI tract affect
the immune system, it may be possible one day to prevent or treat
allergies and inflammatory diseases with diet changes or probiotics -
dietary supplements of 'healthy' bacteria designed to restore the
normal balance of microbes in the gut,'' Huffnagle adds. ''In the
medical community, probiotic therapy is becoming an area of increasing
interest.''

Until then, Huffnagle emphasizes the importance of a healthy low-sugar
diet, with lots of raw fruits and vegetables, after being treated with
antibiotics to help restore the normal mix of microbes in your GI
tract as quickly as possible. ''The old saying, 'an apple a day keeps
the doctor away' may be more true than we thought,'' he says.

Huffnagle's research has been funded by the National Institutes of
Health and a New Investigator Award from the Burroughs-Wellcome Fund.
Other collaborators in the research include Dennis M. Lindell, a U-M
graduate student in immunology, and Rachel Noggle, a research
assistant in internal medicine.








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