Difference between revisions of "Type I Hypersensitivity"
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| + | {{toplink | ||
| + | |backcolour = FFE4E1 | ||
| + | |linkpage =Immunology - WikiBlood | ||
| + | |linktext =IMMUNOLOGY | ||
| + | |sublink1 =Hypersensitivity - WikiBlood | ||
| + | |subtext1 =HYPERSENSITIVITY | ||
| + | |pagetype =Blood | ||
| + | }} | ||
==Introduction== | ==Introduction== | ||
| − | * Also known as [[Immunoglobulin E|IgE]]-mediated or anaphylactic hypersensitivity. | + | * Also known as [[Immunoglobulin E - WikiBlood|IgE]]-mediated or anaphylactic hypersensitivity. |
* Ranges from mild cases, such as hayfever, to life-threatening reactions, such as bee-stings. | * Ranges from mild cases, such as hayfever, to life-threatening reactions, such as bee-stings. | ||
* Antigens that induce a type I reaction are known as allergens. | * Antigens that induce a type I reaction are known as allergens. | ||
* Generally affects face, eyes, nose and feet | * Generally affects face, eyes, nose and feet | ||
| − | * [[Immunoglobulin E|IgE]] has a high affinity to IgE receptors on [[Mast Cells|mast cells]] and [[Basophils|basophils]], and so binds these receptors. | + | * [[Immunoglobulin E - WikiBlood|IgE]] has a high affinity to IgE receptors on [[Mast Cells - WikiBlood|mast cells]] and [[Basophils - WikiBlood|basophils]], and so binds these receptors. |
==Common allergens which elict a type I hypersensitivity reaction:== | ==Common allergens which elict a type I hypersensitivity reaction:== | ||
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[[Image:Sensitisation phase1.jpg|right|thumb|150px|IMAGE 1: Sensitisation phase1.jpg | [[Image:Sensitisation phase1.jpg|right|thumb|150px|IMAGE 1: Sensitisation phase1.jpg | ||
-Brian Catchpole RVC 2008]] | -Brian Catchpole RVC 2008]] | ||
| − | [[Image:Immediate-type hypersensitivity.jpg|right|thumb|150px|IMAGE 2: | + | [[Image:Immediate-type hypersensitivity.jpg|right|thumb|150px|IMAGE 2: Immesdiate-type hypersensitivity-Brian Catchpole/M Maidment RVC 2008]] |
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'''2. Subsequent exposure to the specific allergen (Image 2):''' | '''2. Subsequent exposure to the specific allergen (Image 2):''' | ||
| − | * [[Mast Cells| | + | * [[Mast Cells - WikiBlood|mast cells]] degranulation. |
| − | * [[Basophils| | + | * [[Basophils - WikiBlood|basophils]] with [[Immunoglobulin E - WikiBlood|IgE]] receptors are recruited and also degranulate. |
Mast cells secrete mediators: | Mast cells secrete mediators: | ||
| − | * The release of inflammatary [[Cytokines|cytokines]] which can cause the dog to become itchy. | + | * The release of inflammatary [[Cytokines - WikiBlood|cytokines]] which can cause the dog to become itchy. |
**Steroid mediators, e.g. prostaglandins and leukotriens | **Steroid mediators, e.g. prostaglandins and leukotriens | ||
| − | 1. Chemoattractants (attracts mainly | + | 1. Chemoattractants (attracts mainly neutrophils but also [[Eosinophils - WikiBlood|eosinophils]], [[Monocytes - WikiBlood||monocytes]] and [[Basophils - WikiBlood|basophils]] and plasma) |
| − | |||
2. Vasoactive and inflammatory peptides (e.g. histamine and serotonin) which causes acute contraction of smooth muscle fibres | 2. Vasoactive and inflammatory peptides (e.g. histamine and serotonin) which causes acute contraction of smooth muscle fibres | ||
| − | *If the allergen is inhaled (locally) it can lead to bronchoconstriction. | + | **If the allergen is inhaled (locally) it can lead to bronchoconstriction. |
| − | |||
3. Mucus production - due to the release of mast cell proteases | 3. Mucus production - due to the release of mast cell proteases | ||
| − | |||
4. Vasodilation (leads to redness and heat). | 4. Vasodilation (leads to redness and heat). | ||
| − | |||
5. Oedema (from leaky blood vessels). | 5. Oedema (from leaky blood vessels). | ||
'''3. The late phase response:''' | '''3. The late phase response:''' | ||
| − | * Mediated by [[Eosinophils|eosinophils]]. | + | * Mediated by [[Eosinophils - WikiBlood|eosinophils]]. |
* Takes longer (several hours) as the eosinophils are mobilised from the bone marrow. | * Takes longer (several hours) as the eosinophils are mobilised from the bone marrow. | ||
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===Examples of Type I hypersensitivity=== | ===Examples of Type I hypersensitivity=== | ||
| − | * | + | * Atopy |
| − | * | + | * Flea allergic dermatitis |
| − | * | + | * Sweet itch |
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Revision as of 15:26, 29 August 2008
|
Introduction
- Also known as IgE-mediated or anaphylactic hypersensitivity.
- Ranges from mild cases, such as hayfever, to life-threatening reactions, such as bee-stings.
- Antigens that induce a type I reaction are known as allergens.
- Generally affects face, eyes, nose and feet
- IgE has a high affinity to IgE receptors on mast cells and basophils, and so binds these receptors.
Common allergens which elict a type I hypersensitivity reaction:
- Proteins : Foreign serum
- Plant pollens : Rye grass, ragweed, timothy grass, birch trees
- Drugs : Penicillin, sulphonamides, local anaesthetics, salicylates
- Foods : Nuts, seafood, eggs, milk
- Insect products : Bee venom, wasp venom, dust mites faeces, flea saliva
Mechanism
1. Initial antigen exposure sensitises immune system (Image 1):
- Allergen exposure causes IgE production.
- IgE coat mast cells by binding to Fc receptors.
- Mast cells are now sensitised to this particular allergen.
2. Subsequent exposure to the specific allergen (Image 2):
- mast cells degranulation.
- basophils with IgE receptors are recruited and also degranulate.
Mast cells secrete mediators:
- The release of inflammatary cytokines which can cause the dog to become itchy.
- Steroid mediators, e.g. prostaglandins and leukotriens
1. Chemoattractants (attracts mainly neutrophils but also eosinophils, |monocytes and basophils and plasma) 2. Vasoactive and inflammatory peptides (e.g. histamine and serotonin) which causes acute contraction of smooth muscle fibres
- If the allergen is inhaled (locally) it can lead to bronchoconstriction.
3. Mucus production - due to the release of mast cell proteases 4. Vasodilation (leads to redness and heat). 5. Oedema (from leaky blood vessels).
3. The late phase response:
- Mediated by eosinophils.
- Takes longer (several hours) as the eosinophils are mobilised from the bone marrow.
Examples of Type I hypersensitivity
- Atopy
- Flea allergic dermatitis
- Sweet itch