Hypersensitivity Flashcards
what is hypersensitivity?
exaggerated, inappropriate adaptive immune response that can result in inflammatory reactions and tissue damage.
what are the classifications of hypersensitivity?
type I
type II
type III
type IV
what is type I mediated by?
antibodies
when does type 1 occur?
immediately after exposure
type 1 occurs when what happens?
IgE response to an antigen that wouldn’t normally cause an immune response e.g. pollen, food, latex. IgE binds to high affinity FC receptor on mast cells. Second encounter triggers release of inflammatory mediators producing an acute inflammatory reaction.
treatment for mild type 1 cases?
- Avoidance
- Sodium chromoglycate - stabilises mast cells
- Antihistamines
- Desensitisation: gradually introduce small amount of the known allergen to trigger a different type pf adaptive immune response
what is anaphylactic shock?
severe type 1 reactions with systemic involvement
what are the symptoms of anaphylactic response?
Wheezing, swelling of the face and neck, nausea, dizziness, fainting, low blood pressure
how is anaphylactic shock treated?
adrenaline immediately
why is anaphylactic shock clinically relevant?
Can happen to anaesthetic and latex
what is type II mediated by?
antibodies
what is type II also called?
Antibody dependant cytotoxic hypersensitivity
when does type II occur?
12-18 hrs after exposure to antigen
type 2 occurs when what happens?
when IgG or IgM bind to either a self antigen or foreign antigen on cells. Results in phagocytosis, killer cell activity or complement-mediated lysis. Damage is restricted to particular cells/tissues bearing the antigen.
give an example of type II hypersensitivity
blood transfusions when incompatible blood is transfused
symptoms of type II
fever, hypotension, nausea, vomiting, pain in back or chest
what is type III mediated by?
antibodies
when does type III occur
within 18-24hrs after exposure to antigen
give an example of type III hypersensitivity
extrinsic allergic alveolitis
type III occurs when what happens?
when there is persistence and deposition of antibody-antigen immune complexes. Once deposited can cause severe inflammation
type IV is mediated by what?
T cells and macrophages
what are the two phases that occur during type IV hypersensitivity?
sensitisation phase
elicitation phase
what happens in the sensitisation phase of type IV hypersensitivity?
Antigen is encountered by a dendritic cell in skin, migrates to lymph node, presents antigen to CD4+ helper T cells
what happens in the elicitation phase of hypersensitivity?
Antigen subsequently encountered at a later time, memory T cells triggered and then get inflammation
when does type IV occur?
within 48-72 hrs
but granulomatous take 21-28 days to develop
what are the 3 types of type IV hypersensitivity?
contact
tuberculin
granulomatous
how does contact type IV hypersensitivity present?
as rash at point of contact
how does tuberculin type IV hypersensitivity present?
Presents as skin swelling after intradermal exposure
how does granulomatous type IV hypersensitivity present?
Granuloma formation: aggregation and proliferation of macrophages that can persist for weeks
why is type IV clinically important?
is seen with dental materials
remember there can be more than one type of hypersensitivity happening at the same time
