2. Type 1 Hypersensitivity Flashcards
What type of hypersensitivity reaction is an allergy?
Type I hypersensitivity
In what time frame does a type I hypersensitivity reaction develop after being exposed to a stimulus?
Less than 30 minutes.
What causes a local reaction in a type I hypersensitivity reaction?
Ingested or inhaled allergen.
What causes a systemic reaction in a type I hypersensitivity reaction?
Insect sting or IV administration
What are the antigens in a type I hypersensitivity reaction? Give 3 examples
Environmental, non-infectious antigens:
Seasonal eg tree and grass pollens.
Perennial exposure eg animal dander.
Accidental eg medicines, foods.
What are the two mechanisms behind a type I hypersensitivity reaction?
Abnormal adaptive immune response - TH2 response leading to IgE production.
Mast cell activation - occurring in sensitised individuals. Location of mast cell determines clinical allergic disorders.
What is the hygiene hypothesis?
Children exposed to animals, pets and microbes in the early postnatal period appear to be protected against certain allergic diseases, as exposed to more bacteria so develop TH1 response and no allergy.
What is dysbiosis?
Compositional and functional alterations of the microbiome (eg reduced microbiota), often induced by the western lifestyle.
Where are mast cells found?
Most mucosal and epithelial tissues, and connective tissue surrounding blood cells.
Describe the immune mechanism of an allergic reaction
First exposure to the allergen - TH2 response producing IgE.
Second exposure - IgE cross linking of allergen to mast cell by IgE. Triggers release of granule contents, histamines, chemokines, synthesis of new mediators, leukotrienes and prostaglandins. Lead to increased vascular permeability so hypotension, cardiovascular collapse and generalised urticaria, vasodilation so angioedema, and bronchial constriction so breathing problems.
What causes urticaria? What are the mediators of this?
Mast cell activation within the epidermis.
Histamine and leukotrienes/cytokines.
What does prolonged or chronic exposure to an allergen lead to if causes urticaria?
Atopic dermatitis and eczema.
What is the cause of angioedema? What are the mediators?
Mast cell activation in the deep dermis.
Histamine and bradykinin.
Give an example of a type I hypersensitivity reaction therapy that targets the abnormal adaptive immune response against the allergen?
Allergen desensitisation using oral immunotherapy to correct the TH2 response.
Give anti-IgE monoclonal antibody to target IgE.
Give an example of a type I hypersensitivity reaction therapy that targets the mast cell activation against the allergen?
Anti-histamine.
Leukotrienes receptor antagonists.
Corticosteroids.
