Antibiotics linked to huge rise in allergies
17:06 27 May 04
Source: NewScientist.com news service
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.
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.
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.
James Randerson, New Orleans