Hypersensitivity Flashcards
Define hypersensitivity
Production of an excessive immune /inappropriate immune response causing gross tissue damage when the body meets the antigen for the second time.
Occurs when excessive quantities of antigens of immune system is at a heightened level.
Define allergen
An antigenic substance that produces hypersensitivity, which may be inhaled, ingested or produce a reaction from skin.
Name the types of humoral (antibody mediated) hypersensitivity
Type I - anaphylactic reactions/ immediate hypersensitivity
Type II Cytotoxic
Type III Immune complex reactions
Name the type of cell mediated hypersensitivity
Type IV Delayed hypersensitivity
What is the histology of type I hypersensitivity reaction>
Vasodilation, oedema, eosinophilia, degranulation mast cells
When does type II cytotoxic hypersensitivity occur?
Transfusion reactions, haemolytic disease in newborn, autoimmune and haemolytic anaemias, thrombocytopenia
What are the mediators for a type II hypersensitivity reaction?
IgG,IgA,IgM with or without complement
What is the histology of type II hypersensitvity?
Immunofluorescent staining shows linear deposition of antibody and complement factors on basement membrane
When does a type III reaction occur?
Localised e.g. extrinsic alveolitis or systemic e.g. rheumatoid arthritis or glomerulonephritis.
What is the antigen in Type III reactions?
Extracellular, fungal, parasitic, bacterial or viral
Mediator for type III reactions?
IgG, IgA, IgM with or without complement
What test can you do for type III reaction?
Skin test (intradermal) erythema & oedema
What is the histology of type III reactions?
Acute inflammation reaction with polymorphonuclear infiltration and thrombosis in cases of vasculitis and deposited immune complexes.
When does type IV reaction occur?
Caseation reactions, transplantation rejection and contact dermatitis
What is the antigen in type IV reactions?
Cellular & extracellular
