Allergy Flashcards
What is allergy and hypersensitivity?
Undesirable, damaging, discomfort-producing and sometimes fatal reactions produced by the normal immune system (directed against innocuous antigens) in a pre-sensitized (immune) host.
What are the two immunopathological classifications?
Coombs & Gell 1963- IV types
Extended classification- type V
What is the immunopathogenesis of type ii cytotoxic reactions?
IgG/IgM Ab response against combined self/foreign antigen at the cell surface- complement activation/phagocytosis/ADCC
What are the clinical features of type ii cytotoxic reactions?
Onset minutes to hours
Cell lysis and necrosis
What are the common antigens of type ii cytotoxic reactions?
Penicillin
What are the associated diseases of type ii cytotoxic reactions?
Erythroblastosis fetalis,
Goodpasture’s nephritis
What is the immunopathology of type iii immune complex?
IgG/IgM Ab against soluble antigen- immune complex deposition
What are the clinical features of type iii immune complex?
Onset 3-8h
Vasculitis
What are the associated diseases of type iii immune complex?
SLE
What is the traditional cause of type iii immune complex?
serum sickness
What is the immunopathology of type IV delayed hypersensitivity?
Antigen specific T-cell mediated cytotoxicity
What are the clinical features of type IV delayed hypersensitivity?
Delayed onset 48-72h
Erythema induration
What is the common antigen of type IV delayed hypersensitivity?
Metals-e.g nickel
tuberculin reaction
What is the associated disease of type IV delayed hypersensitivity?
Contact dermatitis
Why do we get allergies?
Those components of the immune system involved in responses to parasitic infection are also involved in allergic responses
The system has developed to produce a rapid tissue-based response to re-infection
The lack of infectious drive (fewer infections) is a contributory factor in allergic disease
What is the immune response to parasitic disease?
Increased levels of IgE - Total - Specific to pathogen – cross-reactive Tissue inflammation with: - eosinophilia & mastocytosis - Basophil infiltration Presence of CD4+ T cells secreting: - IL4, IL5 & IL13
What is the hygiene hypothesis?
Stimulation by microbes is protective
What are the genetic influences on the allergic immune response?
Polygenic diseases Cytokine gene cluster IL3,5,9,13 IL12R; IL4R FcεRI IFNγ; TNF
Are genetic influences sufficient for disease?
NOT sufficient for disease
ONLY susceptibility
What are allergens?
Antigens that initiate an IgE-mediated response
First encounter results in innate & IgM response
What happens in a conventional immune response?
Allergen requires processing
Presentation to T cells & cytokine release
Results in delineation of T-helper subsets into different types
What is the immunopathogenesis of an IgE mediated allergic response?
IgE Ab mediated mast cell and basophil degranulation- release of preformed and de novo synthesized inflammatory mediators
What are the clinical features of an IgE mediated allergic response?
Fast onset (15-30 min) Wheal and flare
