“A new hypothesis argues that allergies emerged to protect us from harmful environmental substances” – Wait for it… Gaia gives us allergies to warn us CO2 makes ragweed grow better and cooks the planet! Whaddawewin? No? Hasn’t come up yet? Give it time.
Ah, glorious springtime. It brings flowers, warmer temperatures—and for many, incessant sneezes and sniffles. Everybody curses allergies as annoying at best, and some allergic reactions—such as anaphylaxis, which rapidly lowers blood pressure and closes the airways—can be fatal. But a handful of researchers now propose that allergies may actually have evolved to protect us. Runny noses, coughs and itchy rashes keep toxic chemicals out of our bodies, they argue, and persuade us to steer clear of dangerous environments.
Most immunologists consider allergies to be misdirected immune reactions to innocuous substances such as pollen or peanuts. Viral and bacterial infections invoke what are called “type 1″ immune responses, whereas allergies involve “type 2″ responses, which are thought to have evolved to protect against large parasites. Type 1 responses directly kill the pathogens and the human cells they infect; type 2 works by strengthening the body’s protective barriers and promoting pest expulsion. The idea is that smaller pathogens can be offensively attacked and killed, but it’s smarter to fight larger ones defensively.
But Ruslan Medzhitov, an immunobiologist at Yale University, has never accepted the idea of allergies as rogue soldiers from the body’s parasite-fighting army. Parasites and the substances that trigger allergies, called allergens, “share nothing in common,” he says—first, there are an almost unlimited number of allergens. Second, allergic responses can be extremely fast—on the scale of seconds—and “a response to parasites doesn’t have to be that fast,” he says.
In a paper published April 26 in Nature, Medzhitov and his colleagues argue that allergies are triggered by potentially dangerous substances in the environment or food to protect us. (Scientific American is part of Nature Publishing Group) As evidence, they cite research including a 2006 study published in The Journal of Clinical Investigation reporting that key cells involved in allergic responses degrade and detoxify snake and bee venom. A 2010 study published in the same journal suggests that allergic responses to tick saliva prevent the pests from attaching and feeding. This mechanism, he argues, is distinct from the classic type 2 response the body uses to defend itself against internal parasites.