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Are Allergies Trying To Protect Us From Ourselves?
By Melinda Wenner Moyer
PLOS Blogs
Posted: April 26, 2012
http://blogs.plos.org/bodypolitic/2012/04/26/are-allergies-trying-to-protect-us-from-ourselves/#more-453

I have a love/hate relationship with spring, thanks to
the aggravating bouts of hay fever that transform me
into a faucet for pretty much the entire season. So I'll
admit I was a little skeptical when my editor at
Scientific American asked me last week if I wanted to
write about a new paper coming out in Nature suggesting
that allergies may actually be a good thing. But always
curious, I said sure.

Turns out it's a fascinating-and pretty convincing-read.
It's dense, but the lead author, Yale immunobiologist
Ruslan Medzhikov, was kind to take a good two hours out
of his day on Monday to explain some of the gnarlier
concepts to me. (Medzhikov is fascinating-you can read
more about him in this profile published in Disease
Models & Mechanisms.)

Medzhikov's basic argument is that there is a convincing
body of research suggesting that allergies have
beneficial effects. They break down the toxic components
of bee, snake, scorpion and gila monster venom, for
instance, and our allergic reactions to tick saliva
prevent the parasites from feeding.

Ultimately, all allergic responses work towards a common
goal: avoidance and expulsion, Medzhitov argues. As I
explain in my piece,

    More generally, hated allergic symptoms keep
    unhealthy environmental irritants out of the body,
    Medzhitov posits. "How do you defend against
    something you inhale that you don't want? You make
    mucus. You make a runny nose, you sneeze, you cough,
    and so forth. Or if it's on your skin, by inducing
    itching, you avoid it or you try to remove it by
    scratching it," he explains. Likewise, if you've
    ingested something allergenic, your body might react
    with vomiting. Finally, if a particular place or
    circumstance ramps up your allergies, you're likely
    to avoid it in the future. "The thing about
    allergies is that as soon as you stop exposure to an
    allergen, all the symptoms are gone," he says.

Obviously, Medzhitov's theory is just a theory, and it
involves a lot of speculation (albeit informed
speculation by a really smart guy). But some research
suggests an association between allergy severity and
cancer risk, in that people with more allergy symptoms
are less likely to develop certain cancers. (One
shouldn't read too much into this though; some other
factor may drive the association. Perhaps people who eat
lots of eggs are more likely to have allergies but less
likely to have cancer.) But all in all, I think
Medzhitov's idea does make sense and is well-supported,
and most of the outside experts I spoke with agreed,
though they did raise questions about some of the
specifics.

One aspect of the theory that I didn't mention in my
piece is that it could explain a medical mystery:
penicillin allergies. Medzhitov argues that in addition
to protecting against venoms, vector-borne diseases and
environmental irritants, allergies also evolved to
protect against a class of toxins called haptens:
proteins that bind to extracellular or membrane-bound
proteins in the body, rendering them useless and
ultimately causing all sorts of problems. As it turns
out, in some people, the penicillin molecule undergoes
transformation into a hapten. This transformation is
very slow and inefficient-very few penicillin markers
turn into haptens, which is a good thing because
haptenated penicillin could be dangerous-but
nevertheless, some people may develop allergic responses
to these few haptenated penicillin molecules, and this
can result in an allergic hypersensitivity to the drug,
Medzhitov posits.

In the case of something like a penicillin allergy,
management is fairly simple (though medically
inconvenient): avoid penicillin. The problem today is
that there may be millions of allergens in the form of
environmental pollutants and irritants, and they may
simply be unavoidable. This idea could help explain why
allergic diseases have become more common in recent
decades: We're exposed to many more pollutants now than
we were 50 years ago, and this chemical flurry could be
dialing up our innate defense systems to a constant
level of 11. An allergy may be protective, but "if it's
taken to an extreme, it is pathological," Medzhitov
says. I wonder, then, if we may have built ourselves a
world that will forever make us sick.

Citations:

Palm, N., Rosenstein, R., & Medzhitov, R. (2012).
Allergic host defences Nature, 484 (7395), 465-472 DOI:
10.1038/nature11047

Medzhitov, Ruslan (2011). Innovating immunology: an
interview with Ruslan Medzhitov Disease Models &
Mechanisms, 4 (4), 430-432 DOI: 10.1242/dmm.008151

Akahoshi M, Song CH, Piliponsky AM, Metz M, Guzzetta A,
Abrink M, Schlenner SM, Feyerabend TB, Rodewald HR,
Pejler G, Tsai M, & Galli SJ (2011). Mast cell chymase
reduces the toxicity of Gila monster venom, scorpion
venom, and vasoactive intestinal polypeptide in mice.
The Journal of clinical investigation, 121 (10), 4180-91
PMID: 21926462

Wada T, Ishiwata K, Koseki H, Ishikura T, Ugajin T,
Ohnuma N, Obata K, Ishikawa R, Yoshikawa S, Mukai K,
Kawano Y, Minegishi Y, Yokozeki H, Watanabe N, &
Karasuyama H (2010). Selective ablation of basophils in
mice reveals their nonredundant role in acquired
immunity against ticks. The Journal of clinical
investigation, 120 (8), 2867-75 PMID: 20664169

Sherman, P., Holland, E., & Sherman, J. (2008).
Allergies: Their Role in Cancer Prevention The Quarterly
Review of Biology, 83 (4), 339-362 DOI: 10.1086/592850

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