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Allergy and Immunology Glossary

Here are definitions of some of the words frequently encountered in literature on allergy and asthma.

Allergy

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.

Anaphylaxis

Anaphylaxis, or anaphylactic shock, is a severe, frightening and life-threatening allergic reaction. The reaction, although rare, can occur after an insect sting or as a reaction to an injected drug - for example, penicillin or antitetanus (horse) serum. Less commonly, the reaction occurs after a particular food or drug has been taken by mouth.

Antibody

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).

Antigen

An antigen is a substance that can trigger an immune response, resulting in production of an antibody as part of the body's defense against infection and disease. Many antigens are foreign proteins (those not found naturally in the body). An allergen is a special type of antigen which causes an IgE antibody response.

Antihistamine drugs

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.

Anti-inflammatory drugs

Anti-inflammatory drugs reduce the symptoms and signs of inflammation. Although not a drug, immunotherapy ("allergy shots") reduces inflammation in both allergic rhinitis and allergic asthma.

Asthma

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.

Bronchitis

Bronchitis is an inflammation of the bronchi (lung airways), resulting in persistent cough that produces consideration quantities of sputum (phlegm). Bronchitis is more common in smokers and in areas with high atmospheric pollution.

Bronchodilator drugs

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

Bronchus

Any of the larger air passages that connect the trachea (windpipe) to the lungs. The plural form of "bronchus" as "bronchi."

Contact dermatitis

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.

Corticosteroid drugs

Corticosteroids are a group of anti-inflammatory drugs similar to the natural corticosteroid hormones produced by the cortex of the adrenal glands. Among the disorders that often improve with corticosteroid treatment include asthma, allergic rhinitis, eczema and rheumatoid arthritis.

Digestive system

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.

Eczema

An inflammation of the skin, usually causing itching and sometimes accompanied by crusting, scaling or blisters. A type of eczema often made worse by allergen exposure is termed "atopic dermatitis".

Epinephrine

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.

Extrinsic asthma

Extrinsic asthma is asthma that is triggered by an allergic reaction, usually something that is inhaled.

Hay fever

See Rhinitis.

Histamine

Histamine is a chemical present in cells throughout the body that is released during an allergic reaction. Histamine is one of the substances responsible for the symptoms on inflammation and is the major reason for running of the nose, sneezing, and itching in allergic rhinitis. It also stimulates production of acid by the stomach and narrows the bronchi or airways in the lungs.

Hives

See Urticaria.

Immune system

The immune system is a collection of cells and proteins that works to protect the body from potentially harmful, infectious microorganisms (microscopic life-forms), such as bacteria, viruses and fungi. The immune system plays a role in the control of cancer and other diseases, but also is the culprit in the phenomena of allergies, hypersensitivity and the rejection of transplanted organs, tissues and medical implants.

Immunoglobulins

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.

Immunotherapy

Immunotherapy ("allergy shots") is a form of preventive and anti-inflammatory treatment of allergy to substances such as pollens, house dust mites, fungi, and stinging insect venom. Immunotherapy involves giving gradually increasing doses of the substance, or allergen, to which the person is allergic. The incremental increases of the allergen cause the immune system to become less sensitive to the substance, perhaps by causing production of a particular "blocking" antibody, which reduces the symptoms of allergy when the substances is encountered in the future.

Inflammation

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.

Intrinsic asthma

Intrinsic asthma is asthma that has no apparent external cause.

Lymphocyte

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.

Mast cell

Mast cells play an important role in the body's allergic response. Mast cells are present in most body tissues, but are particularly numerous in connective tissue, such as the dermis (innermost layer) of skin. In an allergic response, an allergen stimulates the release of antibodies, which attach themselves to mast cells. Following subsequent allergen exposure, the mast cells release substances such as histamine (a chemical responsible for allergic symptoms) into the tissue.

RAST

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.

Respiratory system

The respiratory system is the group of organs responsible for carrying oxygen from the air to the bloodstream and for expelling the waste product carbon dioxide.

Rhinitis

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.

Sinus

The sinuses (paranasal sinuses) are air cavities within the facial bones. They are lined by mucous membranes similar to those in other parts of the airways.

Sinusitis

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

Theophylline

Theophylline is a bronchodilator drug, given by mouth, that widens the airways to the lung. It also is used to prevent attacks of apnea (cessation of breathing) in premature infants and to treat heart failure because it stimulates heart rate and increases urine excretion.

Urticaria

Urticaria is a skin condition, common known as hives, characterized by the development of itchy, raised white lumps surrounded by an area of red inflammation.

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