Allergy and Immunology Glossary

Allergies are inappropriate or exaggerated reactions of the immune system to substances that, in the majority of people, cause no symptoms. Symptoms of the allergic diseases may be caused by exposure of the skin to a chemical, of the respiratory system to particles of dust or pollen (or other substances), or of the stomach and intestines to a particular food.

An antibody is a protein (also called an immunoglobulin) that is manufactured by lymphocytes (a type of white blood cell) to neutralize an antigen or foreign protein. Bacteria, viruses and other microorganisms commonly contain many antigens, as do pollens, dust mites, molds, foods, and other substances. Although many types of antibodies are protective, inappropriate or excessive formation of antibodies may lead to illness. When the body forms a type of antibody called IgE (immunoglobulin E), allergic rhinitis, asthma or eczema may result when the patient is again exposed to the substance which caused IgE antibody formation (allergen).

Antihistamines are a group of drugs that block the effects of histamine, a chemical released in body fluids during an allergic reaction. In rhinitis, antihistamines reduce itching, sneezing, and runny nose.

Asthma is a chronic, inflammatory lung disease characterized by recurrent breathing problems. People with asthma have acute episodes or when the air passages in their lungs get narrower, and breathing becomes more difficult. Sometimes episodes of asthma are triggered by allergens, although infection, exercise, cold air and other factors are also important triggers.

Bronchodilators are a group of drugs that widen the airways in the lungs.

Contact dermatitis is an inflammation of the skin or a rash caused by contact with various substances of a chemical, animal or vegetable nature. The reaction may be an immunologic response or a direct toxic effect of the substance. Among the more common causes of a contact dermatitis reaction are detergents left on washed clothes, nickel (in watch straps, bracelets and necklaces, and the fastenings on underclothes), chemicals in rubber gloves and condoms, certain cosmetics, plants such as poison ivy, and topical medications.

The digestive system is the group of organs that breaks down food into chemical components that the body can absorb and use for energy and for building and repairing cells and tissues.

Epinephrine is a naturally occurring hormone, also called adrenaline. It is one of two chemicals (the other is norepinephrine) released by the adrenal gland. Epinephrine increases the speed and force of heart beats and thereby the work that can be done by the heart. It dilates the airways to improve breathing and narrows blood vessels in the skin and intestine so that an increased flow of blood reaches the muscles and allows them to cope with the demands of exercise. Epinephrine has been produced synthetically as a drug since 1900. It remains the drug of choice for treatment of anaphylaxis.

See Rhinitis.

See Urticaria.

Immunoglobulins, also known as antibodies, are proteins found in blood and in tissue fluids. Immunoglobulins are produced by cells of the immune system called B-lymphocytes. Their function is to bind to substances in the body that are recognized as foreign antigens (often proteins on the surface of bacteria and viruses). This binding is a crucial event in the destruction of the microorganisms that bear the antigens. Immunoglobulins also play a central role in allergies when they bind to antigens that are not necessarily a threat to health and provoke an inflammatory reaction.

Inflammation is the redness, swelling, heat and pain in a tissue due to chemical or physical injury, or to infection. It is a characteristic of allergic reactions in the nose, lungs, and skin.

A lymphocyte is any of a group of white blood cells of crucial importance to the adaptive part of the body's immune system. The adaptive portion of the immune system mounts a tailor-made defense when dangerous invading organisms penetrate the body's general defenses.

RAST is an abbreviation for RadioAllergoSorbent Test, a trademark of Pharmacia Diagnostics, which originated the test. RAST is a laboratory test used to detect IgE antibodies to specific allergens.

Rhinitis is an inflammation of the mucous membrane that lines the nose, often due to an allergy to pollen, dust or other airborne substances. Seasonal allergic rhinitis also is known as "hay fever," a disorder which causes sneezing, itching, a runny nose and nasal congestion.

Sinusitis is inflammation of the membrane lining the facial sinuses, often caused by bacterial or viral infection.