Hypersensitivities Flashcards
Define hypersentivity
- Immunological sensitisation to an allergen which leads to an excessive or inappropriate immune response or hypersensitivity on re-exposure to that antigen.
(it is a type of inflammation that may be acute/ chronic and usually involved skin or respiratory tract)
List some immune mediated diseases of the skin
- Flea allergy dermatitis
- Atopic dermatitis
- Pemphigus
List some of the causes for acute and then chronic hypersensitivity
Acute: contact with/ infection by microorganisms
- Physical e.g. burns, UV light
- Chemical corrosives, irritants
- Tissue necrosis
Chronic: persistent infection by microorganisms
Persistent presence of non living materials
Describe the 2 phases of hypersensitivity
- Sensitisation: Immune system exposed to antigen/ allergen for 1st time, no clinical disease, abnormal IR)
- Re-exposure: immune system re-exposed to same allergen, abnormal IR present and increases, clinical disease apparent
Describe the 2 phases of hypersensitivity
- Sensitisation: Immune system exposed to antigen/ allergen for 1st time, no clinical disease, abnormal IR)
- Re-exposure: immune system re-exposed to same allergen, abnormal IR present and increases, clinical disease apparent
Describe type 1 hypersensitivity
- Localised: e.g. pruritis, bronchoconstriction
- Systemic: anaphylactic shock
- Sensitisation phase= APC captures allergen and takes into LN, presents it to naive T cell, T cell is primed and becomes a TH2 cell. TH2 cell releases IL-4 which triggers B cells to class switch from IgM to IgE. IgE binds to FCe receptor of mast cell. Th2 also secretes IL-5 which stimulates eosinophils.
- Re-exposure phase: Mast cell with IgE attached forms crosslinks when comes into contact with allergen again. Causes degranulation, release of histamine and other pro inflamamtory mediators and attract eosinophils to the area
Give some examples of Type 1 hypersensitivity
- Atopic dermatitis
- Flea allergy dermatitis
- Allergic bronchitis
- Anaphylactic shock
Which breeds are more susceptible to atopic dermatitis?
-Westies, boston terriers
What are intradermal skin tests used for?
Testing for allegens, especially environmental atopy allergens.
Describe Type 2 hypersensitivity
- Requires antibody and cells
- Occurs within 5-10 hours
- Reaction to self antigen or extrinsic antigen
- IgG or IgM produced, binds to target cells. Cytotoxic either due to classical complement pathway OR formation of MAC. Also by ADCC (macropage phagocytosis and NK cell degranulation
Give examples of Type 2 hypersensitvity
- Incompatible blood transfusions in cats
- Haemolytic anaemia
- Myasthenia gravia
Describe ways host cell is destroyed in Type 2 hypersensitivity
-Cytotoxic: Opsonisation/ complement, antibody dependant cell mediated cytotoxicity, phagocytosis, NK cell granules
Describe ADCC
- IgG or IgM bind to self cell- Using Fc region on antigen
- Leaves Fc region exposed which is recognised by FC receptor on NKs or macrophages.
- NK cell will degranulate and macrophage will perform phagocytosis. Both cytotoxic.
-Complement proteins bind to complex= opsonisation
With which hypersensitivity type would you associate haemolytic anaemia?
Type 2
What are the two types of type 3 hypersensitivty?
Antibody excess and antigen excess
