Hypersensitivity Flashcards
What is the definition of hypersensitivity?
An immune response that causes collateral damage to self
What is a type 1 hypersensitivity?
IgE mediated.
Antigen binds to mast cells and releases vasoactive mediators.
What is a type 2 hypersensitivity?
IgG mediated.
Antibodies directed against cell surface antigens.
e.g. blood transfusions, haemolytic anaemia
What is a type 3 hypersensitivity?
Complex mediated.
Antigen-antibody complexes deposited in small vessels.
E.g. SLE, vasculitis, nephritis.
What is type 4 hypersensitivity?
Cell mediated.
T helper 1 cells release cytokines that mediate direct cellular damage.
E.g. contact dermatitis and graft rejection
What is an allergy?
Hypersensitivity specific to the immune system
What timeframe does a true IgE allergy occur within?
Certainly within less than 20 minutes.
Usually instantaneously.
What are common symptoms of IgE allergies?
urticaria, angioedema, wheeze,
What is the treatment cascade for IgE allergy?
Anti-histamine
Hydrocortisone
Adrenaline
What tests are available to ascertain allergens?
History!
IgE specificity
Skin prick (or patch test)
Food challenge test
What is the timescale for a type IV hypersensitivity?
24-48 hours after exposure
What is the pathophysiology of a type IV hypersensitivity?
???
What type of cell is involved in a type IV hypersensitivity?
T cell
What is the most common presentation in dermatology of a type IV dermatitis?
Allergic contact dermatitis
What advice would you give to someone who is allergic to nickel?
Be careful of zips, jean buttons and don’t hold coins in hands for too long or put close to skin e.g. in pockets
