Difference between revisions of "Hypersensitivity - Introduction"
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==Introduction== | ==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]]). | 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]]). | ||
| − | + | 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|(type IV hypersensitivity)]] is not seen for days and is generally cell-mediated. | |
| − | 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 | ||
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''. | 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''. | ||
==Classification== | ==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. | 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. | ||
There are four main types, although a fifth has recently been added. | 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. | Types I, II and III are antibody-mediated; type IV is cell mediated. | ||
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!width="200"|Immune mechanism | !width="200"|Immune mechanism | ||
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| − | | 2-30 min || [[Type I Hypersensitivity|I]] || [[IgE]] mediated | + | | 2-30 min || <center><big>'''[[Type I Hypersensitivity|I]]'''</big></center> || <center>[[IgE]] mediated</center> |
|- | |- | ||
| − | | 5-8 h || [[Type II Hypersensitivity|II]] || [[IgG]] mediated: fixed antigen | + | | 5-8 h || <center><big>'''[[Type II Hypersensitivity|II]]'''</big></center> || <center>[[IgG]] mediated: fixed antigen</center> |
|- | |- | ||
| − | | 2-8 h || [[Type III Hypersensitivity|III]] || [[IgG]] mediated: soluble antigen | + | | 2-8 h || <center><big>'''[[Type III Hypersensitivity|III]]'''</big></center> || <center>[[IgG]] mediated: soluble antigen</center> |
|- | |- | ||
| − | | 24-72 h || [[Type IV Hypersensitivity|IV]] || T cell mediated | + | | 24-72 h || <center><big>'''[[Type IV Hypersensitivity|IV]]'''</big></center> || <center>[[T cells|T cell]] mediated</center> |
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* D.C. Blood and V.P. Studdert'''Saunders Comprehensive Veterinary Dictionary''' Elsevier Science 1999 2nd Edition | * D.C. Blood and V.P. Studdert'''Saunders Comprehensive Veterinary Dictionary''' Elsevier Science 1999 2nd Edition | ||
| − | + | <br><br> | |
| + | {{Jim Bee 2007}} | ||
[[Category:Hypersensitivity]] | [[Category:Hypersensitivity]] | ||
Latest revision as of 17:12, 17 March 2012
Introduction
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. allergy) or directed at self antigens (ie. autoimmunity).
These reactions are antigen specific, occurring only after the immune system has already been sensitised to that antigen. This indicates the 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) is not seen for days and is generally cell-mediated.
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.
Classification
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. There are four main types, although a fifth has recently been added.
Types I, II and III are antibody-mediated; type IV is cell mediated.
| Time of appearance | Type | Immune mechanism |
|---|---|---|
| 2-30 min | ||
| 5-8 h | ||
| 2-8 h | ||
| 24-72 h |
References
Books
- Gareth Kitchen Immunology and Haematology Mosby Elsevier 2007 3rd Edition
- D.C. Blood and V.P. StuddertSaunders Comprehensive Veterinary Dictionary Elsevier Science 1999 2nd Edition
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Originally funded by the RVC Jim Bee Award 2007 |