Parasites pushed into prime time

Worms may be the key to preventing allergies, researchers say.

For years doctors have been saying a little dirt may be good for children, helping to "prime" their immune systems and preventing allergies from developing.

This so-called hygiene hypothesis is based in part on the observation that people in developing countries and those who live in the countryside are less prone to allergies than people who live in modern towns, with their sanitised floors and filtered air.

Allergies are increasing throughout the world. "More than 130 million people suffer from asthma, and the numbers are increasing," Dr Maria Yazdanbakhsh, of the Leiden University Medical Centre, in Leiden, Netherlands, and two colleagues wrote in the journal Science.

Efforts to pin down a cause have failed to find an explanation, not least because, microbiologists say, all the scrubbing in the world does little to reduce the number of bacteria and viruses that get into the body.

But one big difference between people living in poor countries and people living in rich ones is in the number of parasites - especially roundworms, flatworms and pinworms, known collectively as helminths - found in their bodies.

Those parasites may be doing something to the body's immune system to help prime it, and understanding that may be the key to dealing effectively with allergies, Yazdanbakhsh said in an interview.

"It's not that the hygiene hypothesis is incorrect - it's that the immunological explanation up to now is not correct," she said. "The body needs a certain amount of challenge from pathogens. It has to reach a certain set point and if that set point is not reached, something goes wrong."

Dr Yazdanbakhsh, who studies immunology and parasites, said helminths provoked a certain inflammatory response by the body when they infest a person or when a person is simply exposed to them.

She has found some evidence the worms carry important antigens - proteins to which the immune system responds - that provoke a long-term response.

"They live 10 years in your body. Every day they are throwing out these antigens." And it may not be just worms, Dr Yazdanbakhsh said. "I think viruses and bacteria, some of them can do it, too."

Dr Yazdanbakhsh and her colleagues have some theories about what the parasites are doing that helps prevent this immune system overreaction.

"We are working on some molecules," she said. "We have a class of substances that seem to be very potent in inducing anti-inflammatory responses."

Such a molecule might be developed to mimic the immune-priming effects of a parasitic infection "without paying the price of becoming infected with noxious pathogens," Dr Yazdanbakhsh and her colleagues wrote.

- REUTERS

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