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MEDICAL ANIMATION TRANSCRIPT: Our body protects us from many environmental substances such as pollen, foreign chemicals, and pathogens. The immune system is a surveillance system of specialized white blood cells and tissues that recognize self from foreign matter. An antigen is any foreign environmental substance that elicits an immune response. Antibodies are proteins developed by the immune system that recognize and bind antigens. Sometimes our immune system responds excessively to antigens, causing inflammation and tissue damage. This is called an allergic response. Antigens causing an allergic response are allergens. There are four major types of hypersensitivity, immediate, cytotoxic, immune complex, and delayed. The most common type of hypersensitivity is type one, or immediate. This type includes allergies elicited by antigens such as pollen. After initial exposure to this allergen, immune cells create immunoglobulin E antibodies for subsequent exposures. These antibodies are bound to certain white blood cells called mast cells and basophils. Immunoglobulin E encounters and binds to the allergen, triggering the release of inflammatory substances such as histamines, prostaglandins, and leukotrienes from mast cells and basophils. If severe and left untreated, type one can lead to anaphylaxis, an acute, life threatening condition that occurs quickly after antigen exposure and is characterized by low blood pressure and difficulty breathing. Treatment of type one hypersensitivity or allergic reactions induced by environmental substances or biological agents includes treatment of mild symptoms with over-the-counter antihistamines, corticosteroids, or immunosuppressive medications, treatment of severe reactions and anaphylaxis with an epipen, discontinued exposure to the environmental agent, and if the hypersensitivity is in response to a necessary drug treatment, substitution with another agent. In some cases, no reasonable alternative exists, in which case a regimen of desensitization by repeated and monitored exposure to low doses of the drug or agent may be necessary. ♪ [music] ♪