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==Introduction==
==Introduction==
* Also known as [[Immunoglobulin E - WikiBlood|IgE]]-mediated or anaphylactic hypersensitivity.
* 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 - WikiBlood|IgE]] has a high affinity to IgE receptors on [[Mast Cells|mast cells]] and [[Basophils|basophils]], and so binds these receptors.
* [[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:==
[[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: Immesdiate-type hypersensitivity-Brian Catchpole/M Maidment RVC 2008]]
[[Image:Immediate-type hypersensitivity.jpg|right|thumb|150px|IMAGE 2: Immediate-type hypersensitivity-Brian Catchpole/M Maidment RVC 2008]]
'''2. Subsequent exposure to the specific allergen (Image 2):'''
'''2. Subsequent exposure to the specific allergen (Image 2):'''
* [[Mast Cells|Mast cells]] degranulate.
* [[Mast Cells|Mast cells]] degranulate.
* [[Basophils|Basophils]] with [[Immunoglobulin E - WikiBlood|IgE]] receptors are recruited and also degranulate.
* [[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 - WikiBlood|cytokines]] which can cause the dog to become itchy.
* 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|neutrophils]] but also [[Eosinophils|eosinophils]], [[Monocytes|monocytes]] and [[Basophils|basophils]] and plasma)
1. Chemoattractants (attracts mainly [[Neutrophils|neutrophils]] but also [[Eosinophils|eosinophils]], [[Monocytes|monocytes]] and [[Basophils|basophils]] and plasma)
===Examples of Type I hypersensitivity===
===Examples of Type I hypersensitivity===
* [[Allergic diseases - WikiClinical#Allergic diseases#1. Atopic dermatitis - Dogs and horses|Atopy]]
* [[Atopic Dermatitis|Atopy]]
* [[Allergic diseases - WikiClinical#Allergic diseases#2. Flea allergic dermatitis (FAD)- Dogs and cats|Flea allergic dermatitis]]
* [[Flea Allergic Dermatitis|Flea allergic dermatitis]]
* [[Allergic diseases - WikiClinical#Allergic diseases#3. Culicoides hypersensitivity (Sweet itch) - Horses|Sweet itch]]
* [[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}}
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{{Jim Bee 2007}}
[[Category:Hypersensitivity]]