Hypersensitivity Flashcards
Contrast the mechanisms of the different types of hypersensitivity
Type 1- Inappropriate synthesis of IgE (allergy)
Type 2 - IgG or IgM antibodies directed against antigens (self/ external)
Type 3 - Abnormal deposition of formed antigen-antibody complexes in tissues
Type 4 - Delayed reaction- antigens too light so bind to host proteins to produce a response
Describe the pathogenesis of type 1 hypersensitivity
exposure to allergen
mast cell release
Inappropriate synthesis of IgE - allergen specific
Release of inflammatory mediators
What so the mediators cause in type 1 hypersensitivity
capillary leakage vasodilation smooth muscle contraction secretions eg. histamine mucosal oedema
Define atopy
Sub clinical immune sensitisation but NO SYMPTOMS
Describe the mechanism of type 2 hypersensitivity
IgG or IgM antibodies directed against antigens found on the surface of cells or fixed within tissues
What happens once the antibody has bound
Complement system activated
Immunoglobulin binds to Fc receptor and stimulates phagocytosis
Antibody dependent cellular cytotoxicity (ADCC)
Affects cell function (inhibit/stimulate)
Describe the mechanism of type 3 hypersensitivity
Abnormal deposition of formed antigen-antibody complexes in tissues
Complexes are kept soluble in bloodstream and transported (attatched to RBC) to liver and spleen to be phagocytosed/ destroyed
Where are antibody-antigen complexes transported
Liver and spleen
How are antibody-antigen complexes transported
kept soluble in the bloodstream by attachment to RBC
What can cause complex formation
physiological –> normal/ no symptoms/ disease
Pathological –> predisposing factors in either antigen or immune response
Explain the mechanism of abnormal complex formation
Precipitates out into tissue to cause inflammation;
serum sickness and arthus reaction
Describe serum sickness
Systematic illness where complexes are deposited throughout tissue
Describe arthus reaction
More localised response where complexes form locally in tissues (mainly vascular walls)
Describe the mechanism of type 4 hypersensitivity
Occur in response to exogeneous antigens too light to produce a response (haptens) binding to host proteins (carrier)
Define hapten and carrier
Hapten - light antigen
carrier - larger protein
