|
Something in the Air: Airborne
Allergens
Introduction
Sneezing is not always the symptom of a cold. Sometimes, it
is an allergic reaction to something in the air. Experts estimate
that 35 million Americans suffer from upper respiratory symptoms
that are allergic reactions to airborne pollen. Pollen allergy,
commonly called hay fever, is one of the most common chronic
diseases in the United States. Worldwide, airborne dust causes
the most problems for people with allergies. The respiratory
symptoms of asthma, which affects approximately 15 million Americans,
are often provoked by airborne allergens (substances that cause
an allergic reaction).
Overall, allergic diseases are among the major causes of illness
and disability in the United States, affecting as many as 40
to 50 million Americans. The National Institute of Allergy and
Infectious Diseases, a component of the National Institutes
of Health, conducts and supports research on allergic diseases.
The goals of this research are to provide a better understanding
of the causes of allergy, to improve the methods for diagnosing
and treating allergic reactions, and eventually to prevent allergies.
This booklet summarizes what is known about the causes and symptoms
of allergic reactions to airborne allergens, how these reactions
are diagnosed and treated, and what medical researchers are
doing to help people who suffer from these allergies.
What is an allergy?
An allergy is a specific immunologic reaction to a normally
harmless substance, one that does not bother most people. People
who have allergies often are sensitive to more than one substance.
Types of allergens that cause allergic reactions include pollens,
dust particles, mold spores, food, latex rubber, insect venom,
or medicines.
Why are some people allergic to these
substances while others are not?
Scientists think that people inherit a tendency to be allergic,
meaning an increased likelihood of being allergic to one or
more allergens, although they probably do not have an inherited
tendency to be allergic to any specific allergens. Children
are much more likely to develop allergies if their parents have
allergies, even if only one parent is allergic. Exposure to
allergens at certain times when the body's defenses are lowered
or weakened, such as after a viral infection or during pregnancy,
seems to contribute to the development of allergies.
What is an allergic reaction?
Normally, the immune system functions as the body's defense
against invading agents such as bacteria and viruses. In most
allergic reactions, however, the immune system is responding
to a false alarm. When an allergic person first comes into contact
with an allergen, the immune system treats the allergen as an
invader and mobilizes to attack. The immune system does this
by generating large amounts of a type of antibody (a disease-fighting
protein) called immunoglobin E, or IgE. Each IgE antibody is
specific for one particular allergenic (allergy-producing) substance.
In the case of pollen allergy, the antibody is specific for
each type of pollen: one type of antibody may be produced to
react against oak pollen and another against ragweed pollen,
for example.
These IgE molecules are special because IgE is the only class
of antibody that attaches tightly to the body's mast cells,
which are tissue cells, and to basophils, which are blood cells.
When the allergen next encounters its specific IgE, it attaches
to the antibody like a key fitting into a lock, signaling the
cell to which the IgE is attached to release (and in some cases
to produce) powerful inflammatory chemicals like histamine,
cytokines, and leukotrienes. These chemicals act on tissues
in various parts of the body, such as the respiratory system,
and cause the symptoms of allergy.
Some people with allergy develop asthma. The symptoms of asthma
include coughing, wheezing, and shortness of breath due to a
narrowing of the bronchial passages (airways) in the lungs,
and to excess mucus production and inflammation. Asthma can
be disabling and sometimes can be fatal. If wheezing and shortness
of breath accompany allergy symptoms, it is a signal that the
bronchial tubes also have become involved, indicating the need
for medical attention.
|
™