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 bo...