Allergy Flashcards
What are the common names for hypersensitivity I, II, III, IV
I= Anaphylactic II= Cytotoxic III= Immune complex IV= Delayed type
Describe type-II hypersensitivity
- Antibody = IgG, IgM against combined self/foreign antigen
- Antigen= cell surface
- Response time= minutes/hours
- Appearance= lysis & necrosis
- Innocuous antigen= penicillin
- Histology= Antibody & complement
- Associated diseases= Erythroblastosis fettles, Goodpasture’s nephritis
Describe type-III hypersensitivity
- Antibody= IgG, IgM
- Antigen= Soluble
- Response time= 3-8hours
- Appearance= Erythema, oedema, necrosis, vasculitis
- Innocuous antigen= mouldy hay-farmer’s lung
- Histology= Complement & neutrophils
- Associated diseases=SLE
Describe type-I hypersensitivity
- Antibody= IgE
- Antigen= Exogenous
- Response time= 15-30mins
- Appearance= Weal & flare
- Histology= Basophils & eosinophils
- Innocuous antigen= pollen-hay fever
Describe type-IV hypersensitivity
- Antibody= None
- Antigen= Tissue & organ specific T-cell mediated cytotoxicity
- Response time= 48-72 hours
- Appearance= erythema induration
- Histology= monocytes & lymphocytes
- Innocuous antigen= Poison ivy, tuberculin test, metals-nickel
- Associated diseases= contact dermatitis
How does an allergy develop?
- Environmental &/or genetic stimuli
- Barrier dysfunction
- All of above leads to sensitisation
- Leads to changes in T cell sub-sets dominated by Th2
- Causes IgE production
- Forming an allergy
Why do we get allergies?
- Components of immune system involved in responses to parasitic infection also involved in allergic response
- System developed to produce rapid tissue-based response
- Lack of infectious drive is a contributory factor in allergic disease
Describe the immune response to parasitic disease
- Increase levels of IgE specific to pathogen-cross reactive
- Tissue inflammation with basophil infiltration, eosinophilia & mastocytosis
- Presence of CD4+ T cells secreting IL4, IL5, IL13
What is the hygiene hypothesis?
- Stimulation by microbes is protective
- Prevention of autoimmunity by infections
- Pro-biotics in pregnant women
- Mechanism Th1, Th2 deviation
What are genetic influences on the ‘allergic’ immune response?
- Polygenic diseases
- Cytokine gene cluster IL3,5,9,13
- IL12R, IL4R
- FCεRI
- IFNγ, TNF
- Not sufficient for disease only susceptibility
Define allergen
Antigens that initiate an IgE-mediated response, first encounter results in innate & IgM response
What is the conventional immune response?
- Allergen requires processing
- Presentation to T cells & cytokine release
- Resukts in delineation of T-helper subsets into different types
How is IgE produced?
- Th2 cell stimulated by IL4 and interaction with B cell
- B cell proliferation producing IgE
What are the roles of the Th2 T cell?
- Multiple cytokine release
- Innate inflammatory response
- Drive for immunoglobulin production
What diseases are included in the atopic triad?
- Asthma
- Eczema
- Rhinitis