Difference between revisions of "Skin Immunologic - Pathology"

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m (Text replace - "[[Haemorrhage - Pathology" to "[[Haemorrhage")
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===Type I reactions===
 
===Type I reactions===
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*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
 
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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
 
  
 
===Type II reactions===
 
===Type II reactions===
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*Cytotoxic reaction
+
 
−
*[[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]]
 
  
 
===Type III reactions===
 
===Type III reactions===
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*[[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]]
 
  
 
===Type IV reactions===
 
===Type IV reactions===
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*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
 
  
 
==Hypersensitivity reactions==
 
==Hypersensitivity reactions==
  
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===Allergic contact dermatitis===
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===[[Allergic Contact Dermatitis]]===
  
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*Usually involves [[Skin Immunologic - Pathology#Type IV reactions|Type IV reaction]]
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*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]]
  
 
===Atopy===
 
===Atopy===

Revision as of 16:22, 22 February 2011

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General

  • Classification:
    • Hypersensitivity - response to normally harmless substances
    • Auto-immune - antobodies or T-cells reactive against self-antigens
  • Mostly involves mixture of types described below

Type I reactions

Type II reactions

Type III reactions

Type IV reactions

Hypersensitivity reactions

Allergic Contact Dermatitis

  • Usually involves Type IV reaction
  • Pruritic lesions with self-inflicted trauma
  • At areas in contact with allergen
  • Grossly:
    • Erythema, papules, +/- vesicles, exudation -> crusts
    • If chronic, lichenification, hyperpigmentation, alopecia
  • Microscopically:
    • Spongiotic superficial perivascular dermatitis
    • Mononuclear cells
    • If chronic, epidermal hyperplasia
    • May involve eosinophils

Atopy

  • Involves Type I reaction
  • Mainly causes pruritus
  • Dogs - face rubbing and foot licking; secondary pyoderma or seborrhea
  • Cats - facial, ear or generalised pruritus, miliary dermatitis, eosinophilic granuloma complex, symmetric alopecia
  • Horses - pruritic hea, pinnae, ventrum, legs, tailhead or recurrent urticaria
  • Lesions generally due to self-trauma
  • Microscopically:
    • Hyperplastic superficial perivascular dermatitis
    • Mast cells, eosinophils, nonmetachromatic mononuclear cells
    • Perivascular inflammation may be involved especially in horses

Culicoides Hypersensitivity

Flea Bite Hypersensitivity

Autoimmune reactions

Bullous pemphigoid

  • Dogs and horses
  • Involves oral cavity, mucocutaneous junctions, groin and axilla
  • Subepidermal vesicles and bullae
  • Antibodies bound to basement membrane
  • Grossly:
  • Microscopically:
    • Bullae containing fibrin, neutrophils or eosinophils
    • Basement membrane forms floor of bullae and roof is lined with basal cells
  • Bullae may rupture -> ulcers

Dermatomyositis

  • See also Canine dermatomyositis
  • Affects puppies of collies and shetland sheepdogs from 8 weeks of age
  • Lesions - vesiculating dermatitis
    • Face, lips, external ears, later distal extremities
  • Microscopically: interface dermatitis and basal cell degeneration of epidermis and follicular wall, atrophy of follicles, epidermal vesicles and pustules, dermal scarring

Lupus erythematosus

  • Systemic (SLE)
    • Multiple organs involved
    • Cats, dogs, horses
    • Immune dysregulation:
      • Damaged T-cell suppressor function, either primary deficiency or antibody mediated
      • Cytokine dysregulation
      • Resulting B-cell hyperactivity -> antibodies to self antigens -> antigen-antibody complexes deposited in various tissues -> Type III hypersensitivity
    • Lesions localised or generalised
    • Erythema, alopecia, depigmentation, crusting and scaling, ulceration
    • Microscopically: lymphohistiocytic interface dermatitis, thickened basement membrane, vasculitis, subepidermal vesicles, basal cell degeneration
  • Discoid
    • Milder variant of systemic
    • Depigmentation, erythema, scaling, erosions, ulceration, crusting
    • Usually involves nasal planum, dorsum of muzzle, occasionally pinnae, lips, oral mucosa or periocular area
    • Microscopically: lichenoid interface dermatitis, often with lymphocytes, plasma cells, basal cell degeneration, loss of pigment

Pemphigus

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