By James Randerson
NewScientist.com
5-27-4
NEW ORLEANS -- The increasing use of antibiotics to treat
disease may be responsible for the rising rates of asthma
and allergies. By upsetting the body's normal balance of
gut microbes, antibiotics may prevent our immune system from
distinguishing between harmless chemicals and real attacks.
"The microbial gut flora is an arm of the immune system," says
Gary Huffnagle at the University
of Michigan in Ann Arbour. His research group has provided the first experimental
evidence in mice that upsetting the gut flora can provoke
an allergic response.
Asthma has increased by around 160 per cent globally in
the last 20 years. Currently about a quarter of schoolchildren
in the US and a
third of those in the UK have
the condition, but pinning down the causes of the rise has
proved difficult. Some researchers have blamed modern dust-free
homes, while others have pointed to diet.
Antibiotics have been implicated by some epidemiological
studies. For example, the rise in allergies and asthma has
tracked widespread antibiotic use. Furthermore, research
in Berlin, Germany,
has found that both antibiotic treatment and asthma were
low in the east compared to the west when the wall came down.
As antibiotic use has increased in the east though, so has
asthma. This study is particularly valuable because the politically
divided populations were genetically very similar and enjoyed
much the same menu.
Fungal spores
Now Huffnagle has presented experimental
evidence to back up the case. His team gave mice a course
of antibiotics before feeding some of them with a
yeast which is commonly found on human skin.
With the natural gut bacteria suppressed by the drugs, the
yeast became established in the mouse, with no side effects.
Over the course of the following two weeks, the researchers
treated all the mice with spores from a common fungus. Again,
this does not cause disease, but fungal spores can trigger
allergies in people.
The mice whose gut flora had been manipulated, experienced
a much higher immune response to the spores, suggesting that
changes to the collection of microbes in people's guts following
antibiotic treatment might also make us more susceptible
to allergies. "Suddenly, your ability to ignore a mould
spore has gone," Huffnagle told
New Scientist.
The team has repeated the experiments with a second strain
of mice to show that the effect is not dependent on a particular
set of mouse genes. They have also used a different molecule
to produce the allergic response - an egg protein from chickens
called ovalbumin that is commonly
used in allergy research.
In this case, when the team looked at the animals' lung
linings under a microscope the effect of the over-active
immune response was striking. "Their lungs are shredded,
absolutely shredded. I'm sure they can't breath," says Huffnagle.
Training regime
He speculates that our gut bacteria are somehow involved
in training the immune system to ignore harmless molecules
that wind up in our stomach. Precisely how they do this is
a mystery though.
"He's on to a very special track," says Juneann Murphy an expert in stomach bacteria at the University
of Oklahoma in Oklahoma City. "No one else has been
able to make the connections before."
She says the findings reinforce the message that antibiotics
should be used only when absolutely necessary. She also suggests
that patients who have just finished antibiotic treatment
should also receive "probiotic" tablets containing "good" gut bacteria.
Eating foods such as raw fruit and vegetables also helps
to restore the natural balance in our guts. "Once you
are done with the antibiotics you are not finished," adds Huffnagle. "You
need to recover from the treatment itself."
The research was presented at the American Society for Microbiology
general meeting in New Orleans on Wednesday.
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