Allergy Flashcards
What is 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 is the immunopathogenesis of type II (cytotoxic) hypersensitivity?
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 hypersensitivity?
- Onset minutes to hours
- Cell lysis and necrosis
What is a common antigen that stimulates type II reactions?
Penicillin.
What diseases are associated with type II hypersensitivity?
- Erythroblastosis fetalis,
- Goodpasture’s nephritis
What is the immunopathogenesis of type III (immune complex) hypersensitivity?
IgG/IgM Ab against soluble antigen- immune complex deposition.
What are the clinical features of type III hypersensitivity?
- Onset 3-8h
- Vasculitis
What is type III hypersensitivity traditionally associated with?
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 hypersensitivity?
- Delayed onset 48-72h
- Erythema induration
Which antigens are commonly associated with type IV hypersensitivity?
- Metals-e.g nickel
- (tuberculin reaction)
- Poison ivy
What disease is commonly associated with type IV hypersensitivity?
Contact dermatitis
What is the hygiene hypothesis?
- Stimulation by microbes is protective
- Epidemiological data – Increase in Allergy
- Animal Models – T1DM, EAE, Asthma
- Increased atopy (Asthma) after anti-parasitic Rx
- Prevention of autoimmunity (Crohn’s) by infections
- Pro-biotics in pregnant women
- Mechanism – Th1 Th2 deviation
What are the genetic influences on the immune response?
- Polygenic diseases
- Cytokine gene cluster IL3,5,9,13
- IL12R; IL4R
- FceRI
- IFNg; TNF
- 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 to the allergen during 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 immunopathology of type I hypersensitivity (allergic)?
IgE Ab mediated mast cell and basophil degranulation- release of preformed and de novo synthesized inflammatory mediators
What are the clinical features of type I hypersensitivity?
- Fast onset (15-30 min)
- Wheal and flare
What cells are involved in the late phase response?
- Eosinophils
- Central role for Th2 T cell
What is the role of the Th2 cell?
- Multiple cytokine release.
- epithelial cell damage
- airway remodelling
- survival and activation of eosinophils
- bronchial hyperreactivity
What is the atopic triad?
asthma
rhinitis
eczema
What are the features of rhinitis?
- ALLERGIC/NON-ALLERGIC
- ALLERGIC - PERENNIAL or SEASONAL
- Blocked nose, runny nose - often with eye symptoms
- House dust mite, animal danders, pollens
- Treatment – Antihistamines & Nasal steroids
What are the features of asthma?
- Disease of INFLAMMATION and HYPER-REACTIVITY of small airways
- In childhood - AERO-ALLERGIC stimuli - HOUSE DUST MITE key pathogenic importance
- IMMEDIATE symptoms are IgE-mediated
- DAMAGE TO AIRWAYS due to LATE PHASE RESPONSE
- DAMAGED AIRWAYS ARE HYPER-REACTIVE to non-allergic stimuli e.g. fumes
What are the features of atopic dermatitis?
- DERMATITIS – MANY DIFFERENT TYPES
- ATOPIC CONTACT - ALLERGIC/NON-ALLERGIC
- CLINICALLY - Intense itching, blistering/weeping, cracking of skin
- HOUSE DUST MITE now thought to be MAJOR TRIGGER in atopic disease
- Topical Steroids and moisturisers
