Monday, June 29, 2015

Why Do Some People Have Allergies?

Immune System

Human Response: Zimmer writes: “This picture, built up in labs over the past century, answered the ‘how?’ part of the allergies mystery. Left unanswered, however, was ‘why?’ And that’s surprising, because the question had a pretty clear answer for most parts of the immune system. Our ancestors faced a constant assault of pathogens. Natural selection favoured mutations that helped them fend off these attacks, and those mutations accumulated to produce the sophisticated defences we have today.”
Image Credit: Sam Taylor
Source: Mosaic

An article, by Carl Zimmer, in Mosaic looks at the issue of human allergies and interviews an immunologist who has a controversial, but intriguing, theory that essentially says allergies are good for us. That is, they are a long-developed and resident evolutionary response to harmful chemicals, which in some people engender equally harmful or deadly reactions. That today there exist many more harmful or toxic chemicals, many man-made, and many that did not exist 50 years ago ago, might explain why there are many more persons worldwide suffering from allergies.

For example, “Worldwide, sensitization rates to one or more common allergens among school children are currently approaching 40%-50%,” reports the American Academy of Allergy, Asthma & Immunology. The same report says, “Worldwide, sensitization (IgE antibodies) to foreign proteins in the environment is present in up to 40% of the population.”

There are many questions on why this is so; equally important is why some persons have severe allergic reactions (sometimes fatal), while others’ reactions are comparatively mild. We are coming nearer to answering this important question, but we do not know how far we currently are from meeting this objective. We do know that in some persons, the human body’s immune system has an exaggerated, if not aggressive, response to allergens; the essential question is why this occurs? We know the mechanism of what happens; what we do not know is why some persons suffer from allergies—in some cases the response is deadly—and while others do not.

On a personal note, I for one have no known allergies; my wife, on the other hand, has asthma, and a number of allergens can cause an allergic reaction in her. Last week, we took our oldest son, aged 13, to an allergist for testing, who determined that he is highly allergic to horses, and mildly so to dandelions and maple trees. This piqued my interest on this subject.

In “Why Do We Have Allergies?” (April 7, 2015), Zimmer writes:
“That is exactly the problem I love,” Ruslan Medzhitov told me recently. “It’s very big, it’s very fundamental, and completely unknown.”
Medzhitov and I were wandering through his laboratory, which is located on the top floor of the Anlyan Center for Medical Research and Education at the Yale School of Medicine. His team of postdocs and graduate students were wedged tight among man-sized tanks of oxygen and incubators full of immune cells. “It’s a mess, but a productive mess,” he said with a shrug. Medzhitov has a boxer’s face – massive, circular, with a broad, flat nose – but he spoke with a soft elegance.
Medzhitov’s mess has been exceptionally productive. Over the past 20 years, he has made fundamental discoveries about the immune system, for which he has been awarded a string of major prizes. Last year he was the first recipient of the €4 million Else Kröner Fresenius Award. And though Medzhitov hasn’t won a Nobel, many of his peers think he should have: in 2011, 26 leading immunologists wrote toNature protesting that Medzhitov’s research had been overlooked for the prize.
Now Medzhitov is turning his attention to a question that could change immunology yet again: why do we get allergies? No one has a firm answer, but what is arguably the leading theory suggests that allergies are a misfiring of a defence against parasitic worms. In the industrialised world, where such infections are rare, this system reacts in an exaggerated fashion to harmless targets, making us miserable in the process.
Medzhitov thinks that’s wrong. Allergies are not simply a biological blunder. Instead, they’re an essential defence against noxious chemicals – a defence that has served our ancestors for tens of millions of years and continues to do so today. It’s a controversial theory, Medzhitov acknowledges. But he’s also confident that history will prove him right. “I think the field will go around in that stage where there’s a lot of resistance to the idea,” he told me. “Until everybody says, ‘Oh yeah, it’s obvious. Of course it works that way.’”
Or not; as theories go, this one has its share of controversy, it not only being counter-intuitive, but going against the accepted idea that allergies are not good or in no way beneficial to humans—a sentiment shared, no doubt, by the millions of allergy sufferers. The more-accepted theory invokes a combination of genetics or hereditary factors, environmental considerations, and an obsession with hygiene. Even so, Medzhitov defends his position on the protective value of allergies, not giving it any moral weight, but a scientific one, which is dispassionate as it is based on evolutionary theory and, in particular, on natural selection and on the findings of evolutionary biology.

In Medzhitov’s case, he is not looking so much for a cure as an explanation, one being why in some people, the body's human system reacts in such a heightened manner, Zimmer writes, zeroing in on the essential question: “Instead, allergists should be learning why a minority of people turn a protective response into a hypersensitive one.” If scientists and medical researchers can find the answer to this mystery, they will understand an important piece of the puzzle of human development from an evolutionary perspective. To understand is to know with a high degree of certainty; from this point a “cure” might be in sight. What this cure might entail is now hard to say.

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For more, go to [Mosaic]

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