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| | ===Type I reactions=== | | ===Type I reactions=== |
| − | *Mediated by pharmacologically active substances from [[Mast Cells|mast cells]] and [[Basophils|basophils]]
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| − | **Due to antigen-antibody (usually [[IgE]]) binding to receptors on those cells
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| − | *Substances include histamine, serotonin, leukotriens, prostaglandins
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| − | *Can be systemic or local
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| − | *Skin becomes pruritic, raised erythematous borders of wheals
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| − | *Immediate reaction
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| − | *Includes:
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| − | **[[Skin Immunologic - Pathology#Atopy|Atopic dermatitis]]
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| − | **[[Skin Glossary - Pathology|Urticaria]]
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| − | **Angioedema
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| − | **Fly bite hypersensitivity
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| − | **Gastrointestinal parasites
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| − | **Food
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| − | *Microscopically:
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| − | **Capillary dilation, oedema, mast cell degranulation, eosinophil infiltration
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| | | | |
| | ===Type II reactions=== | | ===Type II reactions=== |
| − | *Cytotoxic reaction
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| − | *[[IgG]] and [[IgM]] interaction with antigens bound to cellular membranes
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| − | *Often involves [[Complement#Complement Fixation Pathways|complement fixation]] -> cellular damage
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| − | *In skin - circulating antibody to proteins of desmosomes in intercellular areas along basement membranes at epidermal-dermal junction
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| − | *Includes:
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| − | **[[Skin Immunologic - Pathology#Pemphigus|Pemphigus]]
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| − | **[[Skin Immunologic - Pathology#Bullous pemphigoid|Bullous pemphigoid]]
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| | | | |
| | ===Type III reactions=== | | ===Type III reactions=== |
| − | *[[Complement#Complement Fixation Pathways|Complement fixing]] immune complexes
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| − | *[[IgG]] or [[IgM]]
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| − | *Complexes deposit in tissue -> fix complement -> cytokines and othe factors attrack neutrophils -> release lysosomal enzymes, activation of complement and coagulation, platelet aggregation -> tissue damage
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| − | *Immune complex vasculitis -> [[Haemorrhage#Purpura haemorrhagica|purpura haemorrhagica]]
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| − | *Includes:
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| − | **[[Skin Immunologic - Pathology#Lupus erythematosus|Systemic lupus erythematosus]]
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| − | **[[Skin Immunologic - Pathology#Dermatomyositis|Canine dermatomyositis]]
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| | ===Type IV reactions=== | | ===Type IV reactions=== |
| − | *Delayed hypersensitivity
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| − | *Haptens bind to carrier proteins (mainly epidermal)
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| − | *Mediated by sensitised [[T cell differentiation|T-cells]] -> release cytokines +/- recruit lymphocytes
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| − | *Used in diagnosis of tuberculosis, histoplasmosis and coccidiomycosis
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| − | *Perivascular mononuclear cell accumulation
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| | ==Hypersensitivity reactions== | | ==Hypersensitivity reactions== |
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| − | ===Allergic contact dermatitis=== | + | ===[[Allergic Contact Dermatitis]]=== |
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| − | *Usually involves [[Skin Immunologic - Pathology#Type IV reactions|Type IV reaction]] | + | *Usually involves [[Type IV Hypersensitivity|Type IV reaction]] |
| | *Pruritic lesions with self-inflicted trauma | | *Pruritic lesions with self-inflicted trauma |
| | *At areas in contact with allergen | | *At areas in contact with allergen |
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| | **If chronic, epidermal hyperplasia | | **If chronic, epidermal hyperplasia |
| | **May involve [[Eosinophils|eosinophils]] | | **May involve [[Eosinophils|eosinophils]] |
| | + | |
| | + | [[Category:Type IV Hypersensitivity Diseases]] |
| | + | [[Category:Integumentary System - Hypersensitivity Reactions]] |
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| | ===Atopy=== | | ===Atopy=== |