CP10 - Allergy Flashcards
(49 cards)
what is allergy/hypersensitivity?
undesirable, damaging, discomfort producing and sometimes fatal reactions produced by the normal immune system directed against innocuous antigens in a pre-sensitised host.
what does atopic mean?
allergic
what does innocuous mean?
not harmful
which types of hypersensitivity are most commonly observed in a clinical context?
types I and IV
which types of hypersensitivity are mediated by antibodies?
I, II, III
which types of hypersensitivity are cell mediated?
IV
what is the immunopathology of type I hypersensitivity?
- processed by APC
- presented to T cells
- t cell activation to form Th1,2,17 or Treg (in allergies, thought to only activate the
- the cells generate IL4
- IL4 stimulates B cells to produce IgE
- IgE binds to the allergen
- next time, IgE is already in the system bound to the receptors on sensitised mast cells
- binding of allergen to IgE causes cross linking
- sends the signal to mast cells to release mediators eg. histamine
- 2,d stage is regulated by the arachidonic acid pathway which produces leukotrienes and prostaglandins (late phase)
what are the clinical features oh type I hypersensitivity?
fast onset - 15-30 mins
called wheal and flare, but short lived
what is the immunopathogenesis of type II hypersensitivity?
IgG/IgM response against self or foreign antigen that has adhered to the cell surface (solid medium) , leading to complement activation and phagocytosis or ADCC (antibody dependent cell-mediated cytotoxicity)
what are the clinical features of type II hypersensitivity?
slightly delayed onset - minutes to hours. causes cell lysis and necrosis
which antigen commonly causes type II hypersensitivity?
penecillin
which diseases are associated with type II hypersensitivity?
- Erythroblastosis fetalis - difference in Rh between mum and fetes sensitises her in the first pregnancy and in the second pregnancy, if there is a difference too, her body will react
- Goodpasture’s nephritis
what is the immunopathogenesis of type III hypersensitivity?
IgG/IgM against soluble antigen, not bound to cell leads to formation of immune complexes, which are unable to pass into small blood vessels, causing vasculitis and cell damage in that area
what are the clinical features of type III hypersensitivity?
delayed onset of 3-8 hours, causes vasculitis
what are the common triggers of type III hypersensitivity?
serum sickness, when they injected horse serum as protection from tetanus
which autoimmune condition is associated with type III hypersensitivity?
Systemic Lupus Erythematosus (SLE)
what is the immunopathophysiology of type IV hypersensitivity reactions?
no antibodies involved. APC presents antigen to T cells which develop defences against the antigen and learn to recognise it in later stages
what are the clinical features of a type IV hypersensitivity reaction?
delayed response, 48-72h
erythema induration
which antigens can trigger a type IV hypersensitivity reaction?
metals eg. nickel, causing a tuberculin reaction
which condition is associated with type IV hypersensitivity?
contact dermatitis - reaction caused due to patch testing carried out by dermatologists
how does genetics affect allergies?
- at the level of sensing allergens
- poor barriers (SPINK5 for eczema)
- immune response
- tissue response
are allergies genetic or environmental disorders?
multifactorial, genetics only increases susceptibility
which organs respond to allergens?
- eye - allergic conjunctivitis
- nose - allergic rhinitis
- mouth - oral allergy syndrome
- airways - allergic asthma
- skin - atopic dermatitis
- GI tract - food allergy
what was the initial function of IgE in our body?
to fight parasitic infections
