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鈥檚 immune system. Although we don鈥檛 know precisely how, it appears to promote multiplication of 鈥渞egulatory T-cells鈥�. 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 less badly to allergens and have fewer asthma symptoms.
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To establish a safe dose, Pritchard and nine colleagues infected themselves last year with between 10 and 100 worms, which can grow to a couple of centimetres long and survive for a decade or more. Too many worms and people develop anaemia. 鈥淲e reached the conclusion that you could give 10 parasites safely,鈥� says Pritchard. If a problem develops, drugs will kill off the worms within days, he says.
Pritchard does not know yet whether the worms will permanently reset a person鈥檚 immune system, or whether successive doses will be required. But the trial is the latest to evaluate the potential of live worms. Pig whipworms (Trichuris suis) have been used with considerable success by Joel Weinstock of the University of Iowa to treat the gut diseases ulcerative colitis and Crohn鈥檚 disease, which are triggered by the immune system (麻豆传媒, 10 April 2004, p 8).
