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| − | ==Introduction==
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| − | Hypersensitivity is a hyperactive immune response to an antigen which leads to cell and tissue damage. It involves normal immune mechanisms directed towards harmless environmental antigens (ie. [[:Category:Allergic Diseases|allergy]]) or directed at self antigens (ie. [[Autoimmune Diseases - Introduction|autoimmunity]]).
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| − | These reactions are antigen specific, occurring only after the immune system has already been sensitised to that antigen. This indicates the [[:Category:Adaptive Immune System|adaptive immune system]] is involved, and such responses can be either humoral or cell mediated. Those initiated by antibodies or antibody-antigen complexes are called ''immediate'' hypersensitivity, as the symptoms are seen within hours of exposure. Conversely, the response for ''delayed-type'' hypersensitivity [[Type IV Hypersensitivity - WikiBlood|(type IV hypersensitivity)]] is not seen for days and is generally cell-mediated.
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| − | It is important to note that these responses are part of normal immune defences- in the case of hypersensitivity however the keywords are ''exaggerated'' and ''damaging''.
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| − | ==Classification==
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| − | Hypersensitivity reactions can be classified according to the type of immune mechanism involved, based on a scheme proposed by Gell and Coombs over 40 years ago.
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| − | There are four main types, although a fifth has recently been added.
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| − | Types I, II and III are antibody-mediated; type IV is cell mediated.
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| − | {| border="1" cellpadding="2"
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| − | !width="150"|Time of appearance
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| − | !width="50"|Type
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| − | !width="200"|Immune mechanism
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| − | | 2-30 min || I || [[IgE]] mediated
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| − | | 5-8 h || II || [[IgG]]: fixed antigen
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| − | | 2-8 h || III || [[IgG]] mediated: soluble antigen
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| − | | 24-72 h || IV || T cell mediated
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| − | |}
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| − | ==[[Type I Hypersensitivity - WikiBlood|Type I Hypersensitivity]]==
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| − | '''[[IgE]]''' mediated disease (for more information see [[Type I Hypersensitivity - WikiBlood|Here]])
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| − | ==[[Type II Hypersensitivity - WikiBlood|Type II Hypersensitivity]]==
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| − | '''[[IgG]]''' mediated disease to '''fixed antigen''' (for more information see [[Type II Hypersensitivity - WikiBlood|Here]])
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| − | ==[[Type III Hypersensitivity - WikiBlood|Type III Hypersensitivity]]==
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| − | '''[[IgG]]''' mediated disease to '''soluble antigen''' (for more information see [[Type III Hypersensitivity - WikiBlood|Here]])
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| − | ==[[Type IV Hypersensitivity - WikiBlood|Type IV Hypersensitivity]]==
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| − | '''T cell''' mediated disease (for more information see [[Type IV Hypersensitivity - WikiBlood|Here]])
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| − | ==[[Hypersensitivity Flashcards|Hypersensitivity Flashcards]]==
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| − | ==References==
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| − | Books
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| − | * Gareth Kitchen '''Immunology and Haematology''' Mosby Elsevier 2007 3rd Edition
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| − | * D.C. Blood and V.P. Studdert'''Saunders Comprehensive Veterinary Dictionary''' Elsevier Science 1999 2nd Edition
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| | [[Category:Immunological Disorders]] | | [[Category:Immunological Disorders]] |