2 - Type 1 Hypersensitivity Flashcards
How do you decide what type of hypersensitivity reaction someone is undergoing?
- The trigger
- The timing
- Symptoms
Type I hypersensitivity is known as an allergy (IgE). What are the characteristics of this reaction and what are the different types of reaction?
- Antigen: environmental non infectious antigens (allergen)
- Immediate reaction <30mins
- Local reaction: ingested or inhaled allergen
- Systemic reaction: insect sting or IV administration (bad)
What are some examples of allergens?
People with latex allergy often allergic to vegetable and fruit like potato and kiwi. Due to cross reactive allergens. Called oral allergy syndrome
What are the mechanisms that cause damage in a type I hypersensitivity reaction?
- Abnormal adaptive immune response against the allergens: TH2 response, IgE production
- Mast cell activation: sensitised individuals
- Allergic disorders depend on mast cell location
Why do people in Westernised countries have more allergies than those in developing countries?
- TH1 response in developing countries forming IgG due to all of their exposures
- TH2 respose forming IgE in Westernised world
- DIFFERENT LIFESTYLES
- Also genetics affect allergies as well as environment
What is the hygeine hypothesis?
What are the two most notable factors associated with developed countries to explain the high incidence of allergies?
- Reduced infectious burden: animals, pets and microbes
- Microbial dysbiosis: alteration of the symbiotic relationships with parasites and bacteria
What is dysbiosis?
- Composition and functional alterations of the microbiome
- Often occurs due to Western lifestyle, e.g from junk food, stress, c-sections, urban living, and increases risk to immune diseases and other things (see image)
Where are the strategic locations of mast cells?
- Most mucosal and epithelial tissues - GI tract, skin, respiratory epithelium
- Connective tissue (surrounding blood cells)
- Important role in parasitic infections and inflammation
What are some important mast cell mediators that are involved in an allergic reaction and what are their biological effects?
- Tryptase
- Leukotrienes C4, D4, E4
- Platelet activating factor
- Histamine
What is the immune mechanism of an allergic reaction?
- 1st allergen exposure TH2 response and IgE bind to FCERI receptor on mast cell sensitising them
- 2nd allergen exposure cross-linking of antigen specific IgE causing mast cell degranulation and release of mediators like histamines and leukotrienes that cause changes like vasodilation and increased vascular permeability
- Location of exposure determines allergic reaction response
Urticaria is a skin manifestation of allergic reactions. How is it caused?
- Mast cell activation within the epidermis causing itchy rash
- Mediators: histamine and leukotrienes/cytokines
- If chronic exposure then atopic dermatitis or eczema
Angioedema is a facial manifestation of allergic reactions. How is it caused?
- Mast cell activation in the deep dermis so non itchy
- Mediators = histamine and bradykinin
- Occurs in lip, eyes, tongue and upper respiratory tracts which can be dangerous!!!!
What is anaphylaxis caused by and what are some manifestations of this pathological process?
- Systemic activation of mast cells
- Hypotension
- CVS collapse
- Generalised urticaria
- Angiooedema
- Breathing problems so stridor and wheezing
What is the definition of anaphylaxis and what are some of the signs and symptoms?
Acute onset rapidly progressive allergic reaction involving skin features and at least one other organ system (e.g CVS, GI, Lungs)