If
you're one of the millions of people coughing, sneezing, sputtering, and
cursing your body's hypersensitivity to ragweed, trees, and grass this spring,
researchers at Yale have what could be considered positive news: Seasonal
allergies may be a sign that your immune system is doing what nature intended
it to do -- protect you against environmental toxins that are far more harmful
than pollen.
The paper appears in Nature.
The body’s defense arsenal consists of different
types of immune responses to deal with various classes of pathogens. Type 1
immunity — which battles viruses, bacteria, fungi, and protozoa — relies
primarily on directly killing pathogens or infected host cells.
Type 2 immunity, the focus of this Perspectives
piece, protects against external environmental challenges by spurring the
body’s T cells and antibodies into action to fight the irritant. The problem
is, type 2 immunity can go into overdrive when inadvertently activated by
environmental antigens such as pollen.
Hay fever sufferers know the consequences all too
well: The allergens such as pollen trigger an over-production of histamine,
resulting in the coughing, sneezing, runny noses, and all-round misery that
afflict them most severely in the spring and fall.
Nonetheless, the Yale authors argue that, despite
the occasional misfiring, type 2 immunity is beneficial to humans. They write
that this particular response of the host defense system evolved over time to
protect us from at least four different classes of environmental challenges:
helminthes (parasites), noxious chemicals, animal venoms, and environmental
irritants.
But if type 2 immunity evolved over time to protect
us, what is the purpose of sensing such small amounts of allergen when the
levels are far too low to really harm us, and when a misfiring can cause such suffering?
Lead author Ruslan Medzhitov, professor of
immunobiology at Yale School of Medicine and a Howard Hughes Medical Institute
investigator, said, “We believe that allergic hypersensitivity evolved to
survey the environment for the presence of noxious substances.
After the first exposure, the immune system gains
a memory, and subsequent exposure to even minute amounts will induce an
anticipatory response that helps minimize potentially harmful effects.” He
added that such responses also encourage avoidance of the environment that
contains the noxious substance. “According to this view, hypersensitivity to
allergens triggers avoidance of a sub-optimal environment,” Medzhitov
explained.
More
information: http://www.nature. … re11047.html
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