1b.) Type I Hypersensitvity Flashcards
Allergy is an example of____?
Type I hypersensitivity
How long, following exposure, does it take for a type I hypersensitivity reaction to occur?
<30 mins
Type 1 hypersensitivity reactions can be local or systemic; state some examples of when a local and when a systemic reaction may occur
- Local: ingested or inhaled allergen
- Systemic: insect sting or IV administration
State some examples of allergens, to help you think of examples thing about:
- Seasonal allergens
- Perennial expsoure (lasting for long time)
- Accidnetal exposure
Describe the mechanism of type 1 hypersensitivity reactions
- Initial exposure (as talked about for all hypersensitivty reactions) cuauses priming of T-cells
- In type I, the TH2 cells release interleukins such as IL-4, IL-5 etc…
- Interleukins cause B cells to switch their production of IgM to IgE antibodies specific to the antigen
- IgE antibodies bind to mast cells via FcεRI receptor- sensitising them
- When antigen enters body again it cross links the IgE bound to the sensitised mast cells causing them to release mediators such as histamine, leukotrienes and prostaglandins
- This can lead to widespread vasodilation, bronchoconstriction and increased permeability of vascular endothelium
- The reaction can be divided into two stages:
- Immediate
- Late
Allergies can have different symptoms; explain why
Dependent on mast cell location e..g for asthma the mast cells in lungs are activated
What immunoglobulins do:
- TH1 cells
- TH2 cells
… produce?
- TH1= IgG
- TH2= IgE
It is thought that people in devloping countries are less likely to develop allergies; discuss this
What is the hygiene hypothesis?
Children exposed to animals, pets and microbes in the early postnatal period appear to be protected against certian allergic diseases
Describe the biodiversity hypothesis
Western lifestyle induces alteration of the symbiotic relationshiops with parasites and bacteria leading to dysbiosis o fthe microbiome at mucosal surfaces
*Dysbiosis= compositional and functional alterations of microbiome
Where are mast cells commonly found? (3)
- Most mucosal & epithelial tisues including GI tract, skin & resp epithelium
- Connective tissue surrounding blood vessels
Where are mast cells produced and where do they mature?
- Produced in bone marrow
- Mature in tissue
State the mast cell mediators which you need to be aware of (4) and include which class of product they belong to and their biological effects:
What is required for stem cell survival in tissues (and hence its maturation)?
- Stem cell factor
- Other growth factors determine phenotype of stem cell
What is urticaria?
What causes urticaria?
- Urticaria (also known as hives, wheals) is a skin rash with raised itchy patches of skin due to allergic reaction
- Caused by mast cell activation in the epidermis
- Mediators= histamine, leukotrienes/cytokines
What is angioedema?
What is it caused by?
What mediators are responsible?
- Non-itchy swelling involving skin layers beneath epidermis and/or mucous membranes
- Caused by mast cell activation in the deep dermis
- Mediators= histamine & bradykinin
State some complications of systemic activation of mast cells (which occurs when allergens present in blood circulation)
State some signs & symptoms of anaphylaxis
Summary to be aware of
Describe what oral immunotherapy is
Involves administration of increasing doses of allergen extracts over a period of years, given to patients by injection or droplets/tablets sublingually.
90% effective in patients with bee and wasp venom anaphylaxis
