http://www.newscientist.com/article.ns?id=dn7980

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Dose of worms may ease asthma
10 September 2005
Andy Coghlan
Magazine issue

Allergy-prone people are to be given an innovative therapy: hookworms
that suck blood from their guts.

The idea is that the worms will prime their immune systems so they no
longer react to grass pollen, cat dander and dust mites. A trial of 50 allergy
sufferers in the UK run by David Pritchard and colleagues at the
University of Nottingham will start within weeks, and if it works, researchers
plan to see if the same trick can be used to treat asthma.

Like many parasites, the human hookworm, Necator americanus, has
evolved ways to avoid being killed by the body's immune system. Although we
don't know precisely how, it appears to promote multiplication of "regulatory
T-cells". These in turn suppress other white blood cells that become
overactive in people suffering allergies and asthma. This effect was
first noted in Africa, where researchers found that people infected with the
worms react ...