The word allergy refers to a reaction to an environmen-tal substance, either by breathing it, eating it, or having contact with the skin. The most common mechanism by which an environmental substance causes this kind of reaction involves antibodies, which are proteins formed by the immune system. The normal function of anti-bodies is to protect the body from infection by attacking and killing organisms like viruses and bacteria. In the case of allergy, the antibody is called immunoglobulin E, or IgE, and, rather than attaching itself to microorgan-isms, the antibody binds to normally harmless sub-stances like pollen, dust mites, and animal danders.
Once IgE is formed in the bloodstream, it seeks out and binds to a type of cell called a mast cell, which is located in the mucous membrane of the eyes, nose, lungs, and gastrointestinal tract as well as skin. If the person is then reexposed to that same allergen, the mast cell is triggered within a few minutes to release a variety of chemicals, including histamines, leukotrienes,and prostaglandins . These chemicals, which are also referred to as mediators of the allergic response, are responsible for the symptoms that patients develop after exposure to allergens.
Allergy A type of hypersensi-tivity reaction to environmental sub-stances caused by IgE antibodies.
Antibody
A protein formed by the immune system that helps protect the body from infection and is also responsible for certain types of hyper-sensitivity reactions.
Immunoglobulin E (IgE)
The antibody that is responsible for aller-gic responses.
Mast cell
A type of tissue cell rich in histamine, which is the major cause of immediate allergic reactions.
Histamine
A compound released during allergic reac-tions that causes cap-illary dilation, smooth muscle con-traction, and sensory nerve stimulation.
Leukotriene
A family of lipid mol-ecules, which are released during aller-gic reactions and whose most promi-nent effects are tis-sue swelling and bronchoconstriction.