The effects of helminths on the immune system

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The effect that helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] have on the immune system is complex and more a case of subtle modulation (balancing or quieting) than of suppression. This is achieved by employing an orchestra of chemicals that are excreted/secreted by the worms with the primary intention of keeping them and their host alive and well for as long as possible. The benefits derived by the host as a result of this activity include a reduction of inflammation and the prevention of allergy and autoimmune disease.

What is known about what helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] do is summarised as follows.

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HelminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths], as long-lived parasitesAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.), are remarkable for their ability to manipulate host immunity, protecting themselves from elimination and minimizing severe pathology in the host.[1][2][3][4] Immunomodulation by parasiticAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.) helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] is a general phenomenon that is conserved across species, classes, and even phyla.[5] Therefore, parasiticAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.) infections are a major theme in the hygiene hypothesis. Allergies and autoimmune diseases are less prevalent in countries with higher burdens of helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] and other parasiticAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.) organisms.[6] There are strong epidemiological evidences to support the premise that the dramatic increase in atopic disease in the developed world is a direct consequence of the eradication of helminth infections.[7] At least some helminthes seem to have antiallergic or anti-inflammatory effects in humans. Experimental evidences have also shown the significant suppression for the development of airway hyperresponsiveness (AHR) in mice infected with numerous helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths], including blood fluke Schistosoma japonicum,[8] filaria Litomosoides sigmodontis,[9] nematodeA category of worms with slender, unsegmented, cylindrical bodies that include roundworms and threadworms. Heligmosomoides polygyrus,[10] and Nippostrongylus brasiliensi.[11] These mice show attenuated airway inflammation with reduced infiltration of eosinophilia in the BAL and lung and allergen-specific IgE in sera. Many studies have also demonstrated that helminth infections lower the risk of autoimmunity. Experimental studies have also shown protective effects of helminth infections in animal models of autoimmunity. Surprisingly, helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] have been shown to suppress various types of autoimmune disease, such as collagen-induced arthritis, experimental autoimmune encephalomyelitis, and type 1 diabetes in murine models as reviewed recently.[12] Helminth infections might be beneficial to the induction of multiple regulatory mechanisms, including various regulatory cell populations, inhibitory receptors, blocking antibodies, and two prominent cytokines: IL-10 and TGF-β.[5][13] Thus, it is not surprising that helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] can modulate immunopathology, whether in the context of allergic inflammation or autoimmune disease, either directly or indirectly.[6] (Source)[14]

However, we need to bear in mind that understanding of exactly how helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] produce these effects is still limited. As Elliott & Weinstock have said,

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In most circumstances, little is known regarding the molecular signals exchanged between helminth and host to mediate this process. Even less is known about which helminth products influence disease and how they work.[15]

People considering the use of helminthic therapyThe reintroduction to the digestive tract of a controlled number of specially domesticated, mutualistic helminths (intestinal worms) in the form of microscopic eggs or larvae to reconstitute a depleted biome to treat and prevent chronic inflammation, autoimmune disease and other immunological disorders including allergy. are frequently concerned that the treatment might not be appropriate for them depending on whether they have a condition known to be associated with a Th1 or a Th2 response,[16] but parasiticAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.) infections increase the population of regulatory T-cells, or TREGs,[17] which control the excesses of both Th1 and Th2 cells. This is why helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] can be effective against both allergies and autoimmune diseases.

Another common concern is that helminthic therapyThe reintroduction to the digestive tract of a controlled number of specially domesticated, mutualistic helminths (intestinal worms) in the form of microscopic eggs or larvae to reconstitute a depleted biome to treat and prevent chronic inflammation, autoimmune disease and other immunological disorders including allergy. might reduce a host’s ability to fight other types of infection but, far from making the immune system lazy or less effective, helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] actually make it smarter.

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People who host helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] can still mount an inflammatory attack on pathogens, but they don't set off self-destructive immune bombs against harmless substances or their own cells. (Prof William Parker, Duke University)

References

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