The dirty truth about allergies

A study that compared lab rodents with their wild counterparts could shed light on whether overly hygienic environments cause allergies and autoimmune disease.

Blood tests found more of a particular kind of immune protein in the wild animals, which may mean they are better at coping with potential allergens, researchers say.It is estimated that some 40 to 50 million people suffer from allergies in the US alone. The fact that Western populations appear to have the highest rate of allergies prompted some scientists to come up with the “hygiene hypothesis”, which argues that exposure to more natural environments such as farms early in life helps train the body to respond appropriately to harmless microbes and pollen. In increasingly sterile Western societies, people are no longer exposed to these allergens, which is why they suffer from so many allergies, the hypothesis claims.Wild rodentsTo investigate this, William Parker of the Duke University Medical Center in Durham, North Carolina, US, and his colleagues collected 58 wild rats and 10 wild mice. They extracted blood from the animals and compared serum levels of antibodies with those found in 45 rats and 20 mice bred and raised in the laboratory – which they claim parallels the cleaner environment of modern homes They discovered that the wild rodents had significantly higher levels of IgE and IgG antibodies, which are produced in response to contact with foreign particles, than their laboratory counterparts. The wild rats and mice had 2.5 times and 11.5 times as much IgE as the laboratory rodents, respectively. And they had about double the IgG of their lab-raised counterparts. Previous tests on US hospital personnel and farmers in Rwanda showed that people living in traditional villages also had higher IgE levels than those in modern environments, says Parker, although people who live in hygienic environments and suffer from allergies also have high levels of IgE. Calming effectParker speculates that chronically high IgE levels – from exposure to plant particles and non-lethal microbes in childhood – somehow prevent the immune system from overreacting to them.He adds that a similar process may take place with IgG antibodies, sometimes associated with autoimmune disease.The new findings are worth following up with further studies, says Jean Francois Bach of the Necker Hospital for Children in Paris, France. “The idea that there is a difference between wild and lab animals is significant,” he says. But he adds that the findings do not necessarily support the hygiene hypothesis, since IgE can be elevated by other things, such as parasites.(Source: Scandinavian Journal of Immunology: New Scientist: Roxanne Khamsi: June 2006.)