Allergy Flashcards
What is the definition of hypersensitivity?
An immune response that causes collateral damage to self
What cell or antibody mediates Type I Hypersensitivity?
IgE
What cell or antibody mediates Type II Hypersensitivity?
IgG (mediates Cytotoxic hypersensitivity)
What cell or antibody mediates Type III Hypersensitivity?
Immune complex
antigen-antibody complex
What mediates Type IV Hypersensitivity?
T Cell-mediated
TH1 cells release cytokines to activate macrophages and Tc cells which cause direct cellular damage
How does IgE cause Type I Hypersensitivity?
- Antigen induces crosslinking of IgE bound to mast cells and basophils
- causes degranulation and releases vasoactive mediators
How does IgG cause Type II Hypersensitivity?
- Antibody is directed against antigens on cell
- cell is destructed by either complement activation or ADCC
What is ADCC?
Antibody-dependent cell-mediated cytotoxicity
How does the immune complex cause Type III Hypersensitivity?
- complex is deposited in various tissues
- complement activation
- massive neutrophil migration
Give an example of a typical manifestation of a Type I Hypersensitivity reaction?
- Anaphylaxis
- Local anaphylaxis
e. g. hay fever, asthma, eczema, hives, food allergy
Give an example of a typical manifestation of a Type II Hypersensitivity reaction?
- blood transfusion reaction
- autoimmune haemolytic anaemia
Give an example of a typical manifestation of a Type III Hypersensitivity reaction?
- Localised e.g. Arthus reaction
- Generalised e.g. necrotising vasculitis, rheumatoid arthritis, Systemic lupus erythematosus
Give an example of a typical manifestation of a Type IV Hypersensitivity reaction?
- Contact dermatitis
- Graft rejection
- Tubercular lesions
What causes an allergy?
An allergen
What is the “hygiene hypothesis”?
The thought that developing countries have less allergies as they are more exposed to an allergic environment.
Developed countries have higher levels of antibiotic use and better sanitation => develop more allergies.