Type 1 Hypersensitivity Flashcards
What type of antigen mediates type 1 hypersensitivity reactions?
IgE
What are allergens?
Environmental, non infectious antigens (proteins) that we should not normally react to
What is a type 1 hypersensitivity reaction?
Allergy
Give examples of seasonal allergens
Tree and grass pollens
Give examples of allergens that have perennial exposure (present throughout the year)
- House dust mite
- Animal dander (cats and dogs)
- Fungal spores
Give examples of allergens that have accidental exposure?
- Insect venom
- Medicines e.g. penicillin (any medicine can cause allergy)
- Chemicals e.g. latex
- Foods; milk, nuts, peanuts etc
Explain the mechanism behind type 1 hypersensitivity reactions
- Exposure to antigen- should normally develop TH1 response → IgG that won’t cause allergy
- In hypersensitivity… TH2 mounts a response
- IL-4, IL-5, IL-13
- Produces IgE → drives allergy in subsequent encounter
- Second exposure → IgE drives reaction and mast cell degranulation
How do allergies vary between developing and westerised countries?
Developing country - less likely to develop allergy
Westernised country - more likely to develop allergy.
Hygeine hypothesis → less infectious burden = more likely to have allergy
What is the hygeine hypothesis?
Children exposed to animals, pets and microbes in the early postnatal period appear to be preotected against certain allergic disease
What is microbial dysbiosis seen in western lifestyles?
Western lifestles induce an alteration of the symbiotic relationships with parasites and bacteria leading to a dysbiosis of the microbiome at mucosal surfaces (gut)
Dysbiosis= compositional and functional alterations of microbiome
What happens when mast cells are activated?
Degranulation releasing inflammatory mediators
Where are mast cells strategically located within the body?
Mature mast cells line most mucosal and epithelial tissues - GI tract, skin, respiratory epithelium
In connective tissue surround blood cells
Give an example of an enzyme mast cell mediator
Tryptase
Give an example of a toxic mediator released by mast cells
Histamine
Give examples of lipid mediators released by mast cells
Leukotrienes C4, D4, E4
Platelet activating factor
What are the effects of mast cell degranulation?
Release of histamine and chemiokines, leukotrienes and prostaglandins causes:
- increased vascular permability
- vasodilation
- bronchial constriction
How do allergic reactions manifest on the skin?
Mast cell activation within the epidermis causes urticaria
If exposure is prolonged → atopic dermatitis and eczema
What is angiodema?
Mast cell degranulation in the deep dermis
Mediated by histamine and bradykinin
What are the risks of angiodema?
Angiodema of the lip, tongue and upper respiratory airways can cause life threatening airways obstruction
What are some of systemic manifestations of allergic reaction that lead to anaphylaxis?
- Hypotension
- Cardiovascular collapse
- Generalise urticaria
- Angioedema
- Breathing problems
How do you treat anaphylactic shock?
Adrenaline (epinephrine) IM
How does adrenaline help with anaphylactic shock?
- Reverse peripheral vasodilation and reduced oedema and alleviates hypotension
- Reverses airway obstruction/ bronchospasm
- Increased force of Mycoardial contraction
- Inhibits mast cell activation
What therapies can you give to deal with mast cell activation in allergy?
- anti-histamine
- leukotriene receptor antagonist
- corticosteroids
What therapy can be given to stop the abnormal adaptive immune response against allergens?
- Allergen desensitization (oral immunotherapy)
- IgE mediated- give anti-IgE monoclonal antibodies
What is allergen desensitisation immunotherapy?
The administration of increasing doses of allergen extracts over a period of years
Given to patients by injection, drops, tablets
