Types of hypersensitivity reactions Flashcards
What is type I hypersensitivity
Immediate hypersensitivity (allergy)
when is the onset of type I hypersensitivity
seconds (if IgE is pre-fromed)
What are infectious triggers of type I hypersensitivity
Paracites
Environmental triggers of type I hypersensitivity
Allergens
eg, house dust mite, animal dander, pollen, peanut
What are the adaptive/innate mediators for type I hypersensitivity reactions
Adaptive: Th2 cells, B cells, IgE
Innate: Mast cells, eosinophils
What is type II hypersensitivity
Direct cell killing (cell bound antigen)
type 2 - coming to get u
Antibody binds to cell surface antigen resulting in activation of complement nd opsonisation
What does activation of the complement system by antibodies in type II hypersensitivity result in
Formation of membrane attack complex which punches holes in bacterial cell membranes
Clinical examples of type II hypersensitivity
Immune haemolytic anaemia (eg. giving wrong blood type so complement causes haemolysis of transfused RBC)
Drug induced haemolysis (penecillin induces immune haemolytic anaemia)
How do you manage type II hypersensitivity
Plasmapheresis -removal of pathogenic antibodies
Immunosuppresion
What are the environmental triggers for type II hypersensitivity
Immune haemolytic anaemia
What is type III hypersensitivity
Immune complex mediated hypersensitivity
Presence of excess antigen in blood causes the antibodies to bind forming small immune complexes - get trapped in small blood vessels
Clinical examples of type III hypersensitivity
Farmer’s lung
Inhaled fungal particles from mouldy hay stimulate antibody formation which form immune complexes with antigen
List some causes of hypersensitivity pneumonitis
Farmer’s lung -mouldy hay
Bird fancier’s lung -avian excreta, feathers
Malt workers lung -mouldy malting
Cheese workers lung - mouldy cheese
Maple bark strippers lung-bark from stored maple
What is acute hypersensitivity pneumonitis
Immune complexes deposited in the walls of alveoli and bronchi
Leukocyte accumulation and inflammation within alveoli
Causes wheezing and malaise 4-8hrs after exposure
How to manage type III hypersensitivity reactions
Avoidance
Decrease inflammation - steroids
Decrease production of antibody - immunosuppression
How long till the onset of type III hypersensitivity
Hours - ig IgG is preformed
What are the adaptive immune mediators in type III hypersensitivity reactions
IgG, B cells
What is type IV hypersensitivity
Delayed type hypersensitivity- reaction takes several days to develop
What diseases are associated with type IV hypersensitivity
Autoimmune
Type 1 diabetes
Psoriasis
Rheumatoic arthritis
Non-autoimmune Contact dermatitis TB leprosy Sacroidosis cellular resection of organ transplant
How does type IV hypersensitivity work
T cell mediated hypersensitivity
Initial sensitisation to antigen generated primed effector TH1 cells and memory T cells
Subsequent exposure causes activation of preciously primed T cells and persistent inflammation
How to manage sacroidosis
Watchful waiting - many patients undergo spontaneous remission
NSAIDS - for acute onset
Systemic coticosteroids
- block T cell activation
- block macrophage activation
How long does it take for the onset of type IV hypersensitivity
2-3 days
What triggers type IV hypersensitivity
Infectious - Hep B
enviromental- contact dermatitis
sacoidosis
What adaptive immune cells are involved in type IV hypersensitivity
TH1 cells
