Difference between revisions of "Type I Hypersensitivity"
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==Introduction== | ==Introduction== | ||
| − | * Also known as [[Immunoglobulin E | + | * Also known as [[Immunoglobulin E|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 | + | * [[Immunoglobulin E|IgE]] has a high affinity to IgE receptors on [[Mast Cells|mast cells]] and [[Basophils|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: Immediate-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|Mast cells]] degranulate. |
| − | * [[Basophils | + | * [[Basophils|Basophils]] with [[Immunoglobulin E|IgE]] receptors are recruited and also degranulate. |
Mast cells secrete mediators: | Mast cells secrete mediators: | ||
| − | * The release of inflammatary [[Cytokines | + | * The release of inflammatary [[Cytokines|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 neutrophils but also [[Eosinophils | + | 1. Chemoattractants (attracts mainly [[Neutrophils|neutrophils]] but also [[Eosinophils|eosinophils]], [[Monocytes|monocytes]] and [[Basophils|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. | |
| + | |||
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 | + | * Mediated by [[Eosinophils|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=== | ||
| − | * [[ | + | * [[Atopic Dermatitis|Atopy]] |
| − | * [[ | + | * [[Flea Allergic Dermatitis|Flea allergic dermatitis]] |
| − | * [[ | + | * [[Culicoides Hypersensitivity|Sweet itch]] |
| + | |||
| + | |||
| + | ==From Pathology== | ||
| + | |||
| + | *Mediated by pharmacologically active substances from [[Mast Cells|mast cells]] and [[Basophils|basophils]] | ||
| + | **Due to antigen-antibody (usually [[IgE]]) binding to receptors on those cells | ||
| + | *Substances include histamine, serotonin, leukotriens, prostaglandins | ||
| + | *Can be systemic or local | ||
| + | *Skin becomes pruritic, raised erythematous borders of wheals | ||
| + | *Immediate reaction | ||
| + | *Includes: | ||
| + | **[[Atopy|Atopic dermatitis]] | ||
| + | **[[Urticaria]] | ||
| + | **Angioedema | ||
| + | **Fly bite hypersensitivity | ||
| + | **Gastrointestinal parasites | ||
| + | **Food | ||
| + | *Microscopically: | ||
| + | **Capillary dilation, oedema, mast cell degranulation, eosinophil infiltration | ||
| + | |||
| + | |||
| + | {{review}} | ||
| + | <br><br> | ||
| + | {{Jim Bee 2007}} | ||
| + | [[Category:Hypersensitivity]] | ||
Latest revision as of 17:13, 17 March 2012
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 degranulate.
- 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
From Pathology
- Mediated by pharmacologically active substances from mast cells and basophils
- Due to antigen-antibody (usually IgE) binding to receptors on those cells
- Substances include histamine, serotonin, leukotriens, prostaglandins
- Can be systemic or local
- Skin becomes pruritic, raised erythematous borders of wheals
- Immediate reaction
- Includes:
- Atopic dermatitis
- Urticaria
- Angioedema
- Fly bite hypersensitivity
- Gastrointestinal parasites
- Food
- Microscopically:
- Capillary dilation, oedema, mast cell degranulation, eosinophil infiltration
 |
This article has been peer reviewed but is awaiting expert review. If you would like to help with this, please see more information about expert reviewing. |
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Originally funded by the RVC Jim Bee Award 2007 |