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Adrenaline
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Also known as epinephrine, a hormone which raises the heart rate and constricts blood vessels. Adrenaline is chemically synthesised and used medically as the drug of choice to reverse anaphylaxis.
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Allergen
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Most allergens are proteins which trigger the immune system of an allergic person to produce unwanted symptoms. Examples include grass and tree pollens, house-dust mites and foods such as peanuts, wheat and cows milk.
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Allergy
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Exaggerated or inappropriate reactions of the immune system, medically described as hypersensitivity to specific substances. Allergies are induced in different areas of the body, essentially the respiratory system (e.g. hay fever, asthma), gastro-intestinal tract (e.g. peanut allergies) or the skin (e.g. contact dermatitis).
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Anaphylaxis
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Also known as anaphylactic shock. The most acute reaction to an allergen, resulting from a widespread release of histamine and other biologically active substances which in turn cause breathing difficulties, reduced blood pressure and eventual heart failure. Anaphylaxis often is associated with injected allergens, such as bee/wasp stings or penicillin injections. However, anaphylaxis is a relatively rare reaction which is rapidly reversed by treatment with adrenaline.
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Antibody / Antibodies
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Also known as immunoglobulins (Ig), they are proteins found in the blood which are part of the body's defence that recognises a foreign substance (termed an antigen) and then reacts with it. The antigen is usually an infective agent (e.g. bacteria, viruses). Immunoglobulins are divided into groups A, D, E, G, M. Allergies are most often due to an excessive immunoglobulin E (IgE) response.
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Antigen
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A substance which triggers an immune response as part of the body's protection against foreign substances or organisms. Most antigens are proteins.
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Antihistamine drugs
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The antihistamines comprise a group of chemical agents which block the effects of histamine. Histamine is released by mast cells in the body as a response to an allergic reaction. Formulations of antihistamines may be as tablets, syrups or eye drops.
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Asthma
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A chronic, inflammatory lung disease characterized by breathing difficulties. Acute episodes occur ("asthma attacks") from an impairment in breathing caused by a severe narrowing of airways (bronchi). The episodes may be triggered by a number of factors- such as infection, exercise and cold air- but allergens are now recognised as a major contributor to this condition in many cases.
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Contact dermatitis
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A rash or inflammation of the skin caused by repeated direct contact with a substance. Examples include: detergent residues on clothes, nickel (watch straps and bracelets), rubber gloves and some cosmetics.
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Corticosteroid drugs
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Synthetic hormones also known as steroids; glucocorticosteroids are a subdivision. A group of drugs which exert an anti-inflammatory action by generalised suppression of the immune system. An essentially palliative treatment used for many allergic conditions as well as rheumatoid arthritis. Side-effects can be troublesome. Formulations include tablets, creams, inhalers and eye drops.
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Cromoglycate
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Sodium cromoglycate is mainly used as an inhaler for the prevention of asthma and in nose sprays / eye drops for hayfever. It is a non-steroidal anti-inflammatory drug (NSAID) which stabilizes mast cells, helping to prevent the release of bronchospastic mediators.
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Desensitisation
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Therapy. See Immunotherapy.
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Diagnostic allergy tests
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The two most frequently used allergy diagnosis tests are the skin prick test and the specific IgE blood test. In the skin prick test, a drop of a suspect allergen extract is placed on the patient's arm and a needle is used to gently prick the skin below. An itchy swelling and reddening of the skin after 10-15 minutes indicates a positive result. The blood test evaluates reactivity of circulating IgE to a specific allergen (e.g. RAST, AlaSTAT methods). Other methods employed are the skin patch test and the provocation test.
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Eczema
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An inflammation of the skin that causes itching, a red rash and small blisters that weep and become encrusted. There are several types of eczema, with an allergic form known as atopic eczema or atopic dermatitis. This is often prevalent in babies and young children.
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Hayfever
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Also known as seasonal allergic rhinitis. Symptoms are: sneezing, itching, runny nose and nasal congestion. Pollens are the most prevalent seasonal allergens (e.g. tree pollens, early Spring, or grass pollens, Summer).
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Histamine
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A highly active natural chemical released from the mast cells as a result of an allergic reaction, and a major contributor to the symptoms of allergy. The action may be lessened by palliative treatment with anti-histamine drugs.
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IgE
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The abbreviation of Immunoglobulin E. Most allergic patients have excessive levels of this antibody which is induced to certain allergens they contact. Following an initial sensitisation period, IgE specifically recognising an allergen is made in the body and attaches to the mast cells in the nose, eyes and lungs. Further contact with the allergen results in recognition by the IgE and subsequent release of histamine.
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Immunotherapy
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Also known as specific immunotherapy, desensitization therapy, allergy vaccination and "allergy shots". A preventative treatment, essentially for IgE - mediated conditions such as pollen, house-dust mite and insect sting allergies. Immunotherapy consists of injections of gradually increasing doses of the offending allergen, using a very carefully controlled procedure. The vaccine is thought to work via T-helper cell switching. Modern vaccines now have good safety profiles, through the use of allergoids (allergens chemically modified to reduce the allergic potential) and depot adjuvants (slow-release vehicles). Oral allergy vaccines provide a newer alternative to injection therapy.
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Intolerance
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Normally regarded as an adverse reaction to certain foods but which is not an allergic (IgE-based) reaction in origin. This may be clarified by diagnostic testing for allergies.
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Mpl
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The registered trade name for 3-deacylated monophosphoryl lipid A and is manufactured by Corixa, USA. It is a purified and detoxified adjuvant which has been shown to augment the action of allergy vaccines via a stimulation of "Th1" activity. It is also employed in anti-cancer and anti-infective vaccines.
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Oral allergy vaccines
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A needle-free allergy vaccination therapy attractive to many patients and associated with good safety profiles. A sublingual administration is frequently employed. Formulations use much higher allergen concentrations than comparative injectable vaccines and usually contain flavourings.
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Provocation test
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Also known as a challenge test. A test with an allergen generally performed on the eyes, nose or lungs in order to either accurately diagnose an allergy or to monitor the effect of an allergy treatment. Increasing doses are often used to establish a threshold value of sensitivity.
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Rhinitis
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An inflammation of the mucous membrane that lines the nose, and often occurs as a result of allergy to airborne allergens. Rhinitis can be seasonal (e.g. seasonal allergic rhinitis or hayfever) or can occur all the year round (e.g. perennial rhinitis, allergy to house dust or animals).
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Skin prick test
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See Diagnostic Testing.
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T-helper cells
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Often abbreviated to Th cells, types of lymphocytes (a category of white blood cells involved in generating the immune response). In simplistic terms, allergy vaccination is currently hypothesised to discourage production of Th2 cells (inducing IgE to recognise a specific allergen) and encourage production of Th1 cells (inducing IgG to recognise and deal with the allergen).
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Urticaria
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Also known as nettle rash or hives. An allergic state characterized by itchy raised red patches on the skin which may last for hours or days. Often appears on the face or trunk, and can result from food allergies.
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