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The Curious Connection Between Allergies and Parasites

Proteins in pollen and other allergens show up in tapeworms and mites, suggesting that allergies emerged as we evolved to fight parasite infections.
(Photo: mkrberlin/Shutterstock)

(Photo: mkrberlin/Shutterstock)

Allergies probably aren't on your mind, at least not as we head into winter here in the northern hemisphere. But for some allergies—especially those pertaining to food—a lack of consciousness can be dangerous, even deadly. Doctors are still working on a cure, but in the meantime, perhaps there's (cold) comfort in this: Allergies may be the price we pay for our bodies' ability to fight parasites, according to a new study.

Allergies are basically an immune-system overreaction—hence the rashes, swelling, and so forth—to something others wouldn't react to, like latex, pollen, or peanuts. More specifically, allergies typically involve the overreaction of a particular type of antibody known as immunoglobulin E, or IgE.

The things that trigger allergy attacks are connected to the creepy, crawly creatures that occasionally infect our bloodstreams.

Now, here's the funny thing about IgE: It's also the antibody responsible for fighting off mites and helminths (better known as flatworms, roundworms, and flukes). In other words, the things that trigger allergy attacks are for some reason connected to the creepy, crawly creatures that occasionally infect our bloodstreams. But what connects allergies to helminths? Or, as Nidhi Tyagi and her colleagues ask in PL0S Computational Biology, what makes an allergen an allergen?

To find out, Tyagi, a researcher at the EMBL-European Bioinformatics Institute in the United Kingdom, and her team searched two databases of proteins related to allergies or helminths. The first comprised 2,712 proteins known to kick off allergic reactions. The second database, known as UniProt, contained a total of 70,403 protein sequences from a range of different flatworms, nematodes, and mites.

Comparing the two databases, the team found a total of 2,445 known antigen proteins (out of the first list of 2,712) that shared significant similarities either in sequence—the particular chain of amino acids making up a protein—or physical structure. Put simply, most of the proteins in the stuff that triggers allergies show up in parasites as well.

In addition to that overlap, the researchers realized, there was another way to test the idea. If a protein similar to one in the allergen database showed up in a particular parasite, then it ought to bind to an IgE antibody. To explore that idea, the team looked at Schistosoma mansoni, a water-borne parasite that causes schistosomiasis and also contains a protein, called SmBv1L, very similar to the one responsible for birch pollen allergies. As they expected, the team found that SmBv1L bound to IgE antibodies in the blood of 222 Ugandans infected with Schistosoma mansoni, lending support to the idea that the allergies were closely related to our immune responses to parasites.

"[I]n the absence of the helminth infection, allergenic proteins can be mistakenly targeted by the same arm of the immune system which originally evolved to combat parasitic infection, resulting in an unregulated (sometimes lethal) allergic response," the researchers write. That observation may help doctors better understand—and hopefully treat—allergies.


Quick Studies is an award-winning series that sheds light on new research and discoveries that change the way we look at the world.