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Type I: Anaphylactic Reactions These are the most deadly and are mediated in the circulatory (humoral) system and precipitate by the immunoglobulin IgE antibody. The allergen is usually a protein and the reaction time is in seconds to minutes. There must have been a prior exposure in order for the body to recognize the allergen. The amnestic (second exposure) response is very quick and extreme which is the root of the problem. Anaphylactic shock results in the release of histamines, leukotrienes and prostaglandins; all of which are inflammatory messengers. The manifestations can include nasal dilatation, itching, edema (fluid in tissues), smooth muscle contraction from leukotrienes and prostaglandins, phlegm, pulmonary edema, abnormal heart rhythm, abdominal cramps, shock and death unless treated immediately. This is the immune system waking up an inflammatory response. The treatment is to inject epinephrine (adrenalin) which will rapidly restore breathing and normal heartbeat. An "Epipen" is used to inject epinephrine. An antihistamine is the second line of defense with corticosteroids being the third line of defense. Type II: Cytotoxic Tissue-Specific Reactions These are IgG and IgM immunoglobulin (antibody) humoral mediated reactions. They occur when our own antibodies attack antigens on our own blood components or tissues, such as would happen with an incompatible blood transfusion. Each blood type has different antigens thus transfusing the wrong blood type into someone could be a fatal mistake. The antibodies break open the blood cells, a condition known as hemolysis. Type III: Immune Complex Reactions These reactions involve the IgA or IgM antibodies. When small antibody complexes escape phagocytosis, they can lodge in the basement membrane of certain tissues and destroy cells by creating an inflammatory response. Good examples are rheumatoid arthritis and strep throat. For reference, a basement membrane is part of a cell's outer structure that helps anchor the cells epithelium (skin) to its underlying tissue. Type IV: Delayed Hypersensitivity Reactions Type IV reactions are cell mediated and can take anywhere from 12 to 72 hours to manifest. Allergens are taken up by presenting cells and move to lymph nodes where they induce T-cell production. The new T-cells return to the point of entry where they cause an inflammatory response by stimulation of macrophages and TNF (tumor necrosis factor). Common causes are tuberculosis, poison ivy and rejection of a tissue graft by the host. Testing for and Identification of AllergensTesting to identify the cause of an allergic reaction is centered on either skin or blood. Pin prick or skin puncture is still the most common procedure used to identify allergen specific antibodies. Advantages are that it is more specific, less expensive and simple to administer. Very small amounts of the suspected allergen are placed on the skin at the pin prick sites and, typically, an inflammatory reaction will appear in 30 minutes or so if the person is allergic to the substance. There are several blood testing approaches in use to identify problem allergens. The RAST for "radioallergosorbent test" has been in use for many years and uses antibodies labeled with radioactive isotopes to quantify the levels of IgE antibody in the blood. Other allergic reaction blood tests are based on colormetric or flourometric technologies. Preventing and Treating the Allergic ReactionOnce the cause of an allergic reaction has been isolated, the first and most logical action is avoidance. Unfortunately this is easier said than done for many allergens. Where food is the culprit, avoidance is possible except where the stealth factor comes in. Allergenic proteins can show up in some unexpected places, especially in processed foods. Milk or other dairy products are used in many foods. Peanut oils or extracts can also be present when least expected. Avoidance of animal dander is possible until we pay a visit to someone who has three dogs or cats in the house. With environmental allergens such as pollen, mold, fungi and the like, avoidance may be out of the question. Nevertheless, keeping the house vacuumed, dusted, washing bedding and towels frequently and using air filters can have an impact on allergens in the home. Special care should be taken in sleeping areas to keep the dust mites at bay. Pharmaceutical companies have come to the rescue for many people with various drugs designed to block the action of allergic mediators or prevent the activation of cells and degranulation. These include a wide range of antihistamine products (Zyrtec), decongestants (Sudafed, Mucinex), cortisone, leukotriene inhibitors (Singulair), steroid nasal sprays; the list is endless. Immunotherapy is often used to mitigate the allergic reaction by attempting to desensitize the body to the specific allergen. This approach involves a series of shots or vaccinations starting with very small doses of the allergen and building up to larger infusions. The hope is that the body will respond by producing antibodies to the allergen and thus decrease or eliminate the allergic reaction. The Hot New DevelopmentThe first knee-jerk reaction from the medical community is to look for a new drug and the pharmaceutical companies are always happy to oblige. The big breakthrough is that a new class of drugs called "anti-IgE" therapies show promise in treating rhinitis, food, skin and asthma type allergic reactions. One such drug that should hit the market soon is Xolair, assuming the FDA approves it. But guess, what? It will likely cost you $10,000 a year and insurers are not likely to cover it for allergies. Wouldn't it be so much better to see our research dollars go toward prevention and nutrition instead of investing hundreds of millions of dollars on a new drug that no one can afford? Let's figure out how not to get an allergy in the first place.
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