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Anaphylaxis is a severe, whole-body allergic reaction. After initial exposure to a substance such as wasp sting toxin, the allergic child's immune system becomes sensitized to that allergen. On a subsequent exposure to the specific allergen, an allergic reaction, which can involve a number of different areas of the body, occurs. Anaphylaxis is thought to result from antigen-antibody interactions on the surface of mast cells, connective tissue cells that are believed to contain a number of regulatory, or mediator, chemicals. Specifically, an immunoglobulin antibody protein, IgE, is produced in response to the presence of the allergen. IgE binds to the mast cells, causing them to suddenly release a number of chemicals, including histamine, heparin, serotonin, and bradykinin. Once released, these chemicals produce the bodily reactions that characterize anaphylaxis: constriction of the airways, causing wheezing and difficulty in breathing; and gastrointestinal symptoms, such as abdominal pain, cramps, vomiting, and diarrhea. Shock can occur when the released histamine causes the blood vessels to dilate, which lowers blood pressure; histamine also causes fluids to leak from the bloodstream
Substances that can trigger an anaphylactic reaction include:
Anaphylactoid (meaning "anaphylactic-like") reactions are similar to those of true anaphylaxis but do not require an IgE immune reaction. These are usually caused by direct stimulation of the mast cells. The same chemicals as with anaphylaxis are released, with the same effects, so the symptoms are treated the same way. However, an anaphylactoid reaction can occur on initial exposure to an allergen as well as on subsequent exposures, since no sensitization is required.
There is also a rare kind of food allergy, called exercise-induced allergy, that is caused by eating a specific food and then exercising. It can produce itching, lightheadedness, hives, and anaphylaxis. The offending food does not cause a reaction without exercise, and, alternately, exercise does not cause a reaction without ingesting the food beforehand.
Author Info: Judith Sims, Thomson Gale, Gale, Detroit, Gale Encyclopedia of Children's Health, 2006
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