Wednesday, February 29, 2012

Parasite helps us to repress allergies

Allergies are caused by an immune system that is overreacting to something that does not pose a real threat. A common form is being allergic to house dust mite, a little bug that creeps around your bedroom and in carpets. There is a reason the immune system normally lies dormant: when it stirs up a war against something foreign, it drains all your energy and leaves you feeling ill. In extreme cases, the immune response can be so heavy that it causes death, which can happen when pathogens enter the bloodstream during sepsis. Luckily, allergies normally aren't that bad. Also, not all bugs or microbes are necessarily bad. Scientists from the University of Edinburgh have found that some bugs actually help us to repress allergies. It appears as if they are training our immune system.

The bugs in question are helminth, commonly known as parasitic worms. It is not something you'd want to have crawling around in your body, but peculiar enough, it also helps us by instructing the immune system to not respond to certain allergens. Researchers found that groups of people with a higher exposure to helminths also had lower level of allergies. It is as if the bug tells the immune system to back off. This is beneficial, of course, for the parasitic worm because it likes the free ride in our body.
Hookworms, present in the intestine.
When investigating the role of the helminths on human health, the scientists actually set out to unravel why it causes health problems. Its effect on dampening the allergic response was a surprising one. The worms are known to cause infectious diseases, and their ability to reduce the immune response may play part in it.

Even though helminths appear to be able to decrease allergic responses, it is not necessarily a good idea to go around exposing people to these infectious worms: it is still not very healthy to have them crawling around in your intestines, feeding off what you eat. However, we know what helminths look like, and therefore we may be able to unravel what it is that causes the immune system to back down when our body is exposed to parasitic worms. In turn, we may use the mechanism to artificially reduce the allergic response in patients.

It is not the first time exposure to bugs and microbes is associated with a decrease in allergies. According to the so-called Hygiene Hypothesis, exposure to pathogens in early life leads to a decrease in allergies later on. It is as if the immune system needs to be trained to be able to correctly assess how and when to respond. Because human beings have increasingly upped the hygiene standard, some kids do not come into contact with pathogens anymore. This is supposed to be the cause of the increase in allergies. Basically, the immune system consists of a balance: there is a type I response and a type II response. Type I is directed against most pathogens, while type II is thought to promote allergy. If the balance is tipped towards type I, which happens when exposed to pathogens, type II will not get a chance. However, without exposure to pathogens, the immune system may resort to the allergic type II response. 

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