Allergy Flashcards
Allergy?
‘disease following a response by the immune system to an otherwise innocuous antigen’
Where do allergies reside?
Allergies reside within hypersensitivities, defined as ‘harmful immune responses that produce tissue damage.’
What are the 4 types of hypersensitivity reaction?
Type 1 = IgE
Type 2 = IgG
Type 3= IgG
Type 4= driven by T cells (no evidence of antibodies involved)
What are allergies mediated by?
When does it take place?
IgE
- always occurs on exposure to an allergen, so an initial exposure event has always taken place.
Where are allergies common?
In the west,,
Often between 25% - 50% of the population have an allergy
-
When do allergies occur?
When IgE triggers mast cell degranulation
(Preformed granules can be released upon triggering)
What is IgE produced by?
Plasma B cells in lymph nodes or locally at site of inflammation.
Where is IgE located?
What is it bound to?
- Mostly in tissues (hence low serum concentration)
- bound to mast cell surfaces through high affinity IgE receptor Fc3R1
What will favour production of IgE?
What do the Th2 cells also do?
- certain antigens and routes of delivery (eg- transmucosal at low doses is often a common route)
- CD4+ T cells of the Th2 phenotype that produces IL4 cytokines favour IgE responses.
- Th2 T cells also force B cells to switch the isotope of the Ig they secrete from IgM to IgE
What 3 molecules will effector T cells produce?
CD8 cytotoxic = IFNy, TNFa (target cell lysis)
CD4 Th1= IFNy, GM-CSF, TNFa (macrophage activation)
CD4 Th2= IL4, IL5 (B cell activation)
What are common inhaled allergens?
-plant pollens
- dander of domesticated animals
- mol spores
- feces of very small animals (house dust mice)
Common allergens of injected materials?
- insect venoms
- vaccines
- drugs
- therapeutic proteins
Common allergens of ingested material?
Common allergens of contacted materials?
Ingested = food, orally administered drugs
Contacted materials=
- plant leaves
- products made from plants
- metals
What are the 6 features of some inhaled allergens?
Protein = only proteins induce T cell responses
Enzymatically active= allergens are often proteases
Low dose = favours IL4 producing CD4 T cells
Small size = allergens can diffuse out of particle
Highly soluble = elites readily from particle
Stable = allergen can survive desiccation.
why is IgE a major part of the host defence?
- IgE is thought to be crucial in host defence against parasites, many of which gain access by secreting proteolytic enzymes.