You are here: MEDICA Portal. MEDICA Magazine. Topic of the Month. Volume archives. Our Topics in 2010. December 2010: The Immune System. Allergy.
Parasitic worms in the service of science
Many people are disgusted when they see a worm in their food. The idea of being the host of one is all the more appalling; © panthermedia.net/Christian Lötte
In the so-called developing countries, vermicular diseases are still common in many people today. The parasites or endoparasites, respectively, live in cavities or in the blood for instance. Intestinal parasites like the tapeworm adhere to the inside of the intestine. Although it does not reproduce there, the immune system of course is going to try to excrete the foreign matter again. But this is exactly why parasites use a clever trick – they secrete messengers, which down-regulate our immune system.
After all, it is a normal immune system response to produce antibodies against foreign substances, which render the intruder harmless. Yet this usually cannot kill off an endoparasite, like for instance a tapeworm. However, cohabitation with the parasites becomes possible. And even if it doesn’t sound pretty, both – human being and parasite – benefit from this arrangement. The parasite stays alive and the human barely reacts with discomfort, but continues to live normally. But beyond that, the reduced activity of the immune system seems to have another consequence for human beings: they react less allergic to their environment. Allergies occur noticeably less for instance in people in the Third World. This is why the drastic increase of allergies in Europe is attributed to the constantly improving hygiene precautions. But is this theory valid and how can the gained knowledge be put into action?
Scientist’s hope lies in finding a
way to extract active intestinal
parasites to be able to produce
a drug; © panthermedia.net
Scientists in action
In their search for evidence, scientists sometimes take some unusual approaches. Professor David Pritchard from the University of Nottingham for instance, deliberately infected himself with hookworm larvae to prove that they are suited for treating disorders of the immune system, for instance asthma or Crohn’s disease, because they would stimulate the part of the immune system that’s in charge of the entire “defense“.
In a publication in the University’s own magazine “Vision Magazine/Edition 9“, Pritchard is quoted as follows: “ The driving force of any immune response is a cell called the T-cell. T-cells called T-helper 1 fight bacteria – and if that part of the immune system over-reacts you get diseases like Crohn’s, psoriasis, and rheumatoid arthritis. On the other side are T-helper 2 cells which fight worm infection, but when this side of the immune system overreacts you get allergies. In the middle is a more recently discovered population of T-cells called regulatory T-cells. These keep everything in check. Our hypothesis is that the worms are expanding the population of regulatory T-cells to down-regulate the rest of the immune response. “
Whether this is actually the case however is not yet conclusively investigated, as Professor Peter G. Kremsner, Institute Director of the Institute for Tropical Medicine in Tübingen explains on inquiry:”You can only speculate. The idea has been around for a long time. But we still don’t know exactly whether T cells are in fact responsible for the down-regulation of the immune system. Even though the T2 immune response increases the regulatory response in the event of a parasite infestation and the inflammatory response is partially lowered, which benefits patients with allergies or autoimmune diseases –nitric oxide also acts in a similar way. An exact conclusion about the underlying mechanism is always difficult with complex microorganisms. “
The hope for a drug
Behind every research there naturally is the desire to produce a pharmaceutical remedy, to also be able to offer allergic persons an effective treatment. After all, so far there are no treatments that are 100 percent effective. Kremsner sums it up like this: “There is hope that we can either develop extracts in vitro or place worms into the intestines, which eventually die off again on their own. The latter might not sound so nice, but the psychological strain of many allergic persons is certainly strong enough to also consider this option. Unfortunately, thus far there is no successful clinical trial confirming this. But I think that this approach offers big potential. For people who suffer from multiple allergies, there is no curative treatment at this point, only a pure symptomatic treatment. That’s why this approach should definitely be pursued and researched with combined efforts. “
Whether this approach ultimately will proof effective, remains to be seen. Until then, people who for instance can call a tapeworm their very own, may want to believe that everything also has a good side.
(Translated by Elena O'Meara)