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.