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In Type I, (IgE-Mediated) Immediate Hypersensitivity allergies, the antibody immunoglobulin E (IgE) is produced within minutes of exposure. When an allergic individual breathes in the pollen or other allergen causing his problem, his immune system signals B lymphocytes to produce IgE antibodies specifically designed to target the allergen’s protein molecules. These IgE antibodies then become attached to the surfaces of mast cells in the respiratory and gastrointestinal tracts and to eosinophils, comparable cells in the bloodstream. During future exposures, the allergen will bind to the waiting IgE antibody receptors, triggering the release of histamine from mast cells and eosinophils. As a result, swelling, itching, redness, pain, watery eyes and nose, muscle contractions, and capillary permeability occurs as the body tries to rid itself of the allergen.
Type I “classic” allergies are usually the result of reactions to airborne allergens including mold, pollen, dust mites, and
animal dander. The same type of allergic reactions are also caused, in some people, by milk, eggs, corn, nuts, peanuts,
strawberries, and chocolate. Pharmaceuticals such as penicillin (derived from mold) and aspirin, together with insect stings and latex, can also cause the worst form of Type I allergic reaction, anaphylaxis. This requires immediate adrenaline injections to reverse the symptoms caused.
In Type II, Cytotoxic Allergies, antibodies inject toxic protein enzymes (cytotoxin) into antigen cells, which kills them. If
this process occurs in blood or tissue cells, it can result in immune hemolytic anaemia when too many red blood cells die.
Intestinal cells often suffer the most damage from cytotoxic reactions because many of the allergens involved are foods.
In Type III, Arthus Allergies, the reaction may occur as much as 10 days after exposure. As in Type II, the antibody IgG binds to an invading protein, but in this case forms a circulating immune complex. In persons with weakened immunity, such complexes can build up in the bloodstream. If the kidneys cannot excrete them adequately they accumulate in the soft tissues, causing inflammation and symptoms such as hives, joint pain, headaches, fatigue, and even arthritis. It is estimated that approximately 80 percent of food allergies are Type III reactions.
In Type IV, Cell-Mediated Allergies, symptoms typically appear 2 to 3 days following exposure. The main triggers of such
allergies are various plants, including poison ivy, and some pharmaceutical drugs. These allergies can result in allergic
contact dermatitis, allergic colitis, Crohn’s disease, and grafttransplant rejections. In such reactions, T cells directly attack an antigen. Since it takes about a day for the body to amass adequate T cells in the affected area, allergic symptoms (usually allergic contact dermatitis) are experienced some 1 to 3 days after exposure. Approximately 3,000 substances are known to be able to cause this type of allergy, ranging from mercury and nickel, through rubber and plastic, hair dyes, cosmetics, and latex. Various foods, such as pineapples, bananas, papaya, kiwi, and avocado, are also contact allergens in some sensitive individuals.
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