Hypersensitivity responses Flashcards
What are all hypersensitivity reactions involved in?
Adaptive immune response
What is type 1 hypersensitivity mediated by?
IgE
What is type 2 hypersensitivity mediated by?
IgG
What is a type III hypersensitivity reaction?
Type III hypersensitivity is an immune complex-mediated reaction in which an antigen-antibody complex lodges in tissue, activating complement and attracting phagocytes that cause tissue damage.
What is a type IV hypersensitivity reaction?
T cell mediated reaction.
What is the process of the adaptive immune response from APC to B cell activation.
APC presents antigen to T cell
Activation of T cell, production of cytokines.
T cell help
- Th1/Th2/Th17 (see perio)
Cytotoxicity CD8 T cells
B cell activation - antibody production
What is the initiating event for an IgE response?
Soluble antigen
Triggers IgE response, IgE binds to cell surface of mast cells.
Re-exposure to same antigen, interaction with IgE on mast cells
Degranulation
How is IgE bound to mast cells?
FceR1
What are some mediators of type 1 allergy?
IL-4, IL-13 -Th2 response
IL-3, IL5 - eosinophil synthesis
TNF a
Lipid mediators - leukotrienes
What is a specific marker of mast cell degranulation?
Mast cell tryptase
What is mast cell tryptase useful for?
Investigation of anaphylaxis
What is result of high IV allergen dose?
systemic anaphylaxis
What is outcome of SC low dose allergen?
local wheal & flare - due to histamine
What is type 1 response due to inhalation of allergen?
Bronchospasm - asthma
What is type 1 response to ingestion of allergen?
diarrhoea and vomiting
five two examples of type 1 hypersensitivity?
allergic rhinitis
Anaphylaxis - systemic response to antigen
What is the outcome of anaphylaxis?
Widespread increase in capillary permeability
Vasodilation
Potentially fatal hypotension
What are two types of type II sensitivity?
IIa - cytotoxic
IIb - cell stimulating
What is type IIa hypersensitivity?
IgG antibody interacting with surface antigen
Binding of IgG leads to lysis of target cell due to activation of complement, macrophage binding to the FcR portion of IgG and phagocytosis occuring.
Give some examples of type IIa hypersensitivity?
Allergic drug reactions
Incompatible blood transfusion
Autoimmune haemolytic anaemia
What is the mechanism of type IIb hypersensitivity?
IgG mediated, binds to cell surface receptor involved in cell signalling.
Antigen cell associated.
IgG may be agonist or antagonist.
Give some examples of type IIb hypersensitivity reactions?
Graves disease, agonist thyroid stimulating immunoglobin.
Myasthenia gravis
- antagonist Anti-AChR antibody.
Give an example of type III hypersensitivity reaction
Rheumatoid arthritis - inflammation in joints
Immune complex glomerulonephritis
What is the mechanism of type III hypersensitivity?
Antibody-antigen immune complexes
Deposit in microvasculature
Activate complement
Cause tissue inflammation + attraction of neutrophils
What is type IV Th1 hypersensitivity response?
Delayed hypersensitivity
Antigen presentation to activated CD4 Th1 cell
Soluble antigen
Th1 cytokine production and release
Macrophage activation
Macrophage rich inflammatory response
What is type IV Th2 hypersensitivity response?
Chronic allergic inflammation
Antigen presented to sensitised CH4 Th2 cells
Th2 cytokine release IL-4, IL-5, IL-13
- Eosinophil rich inflammatory response
What are some examples of type IV Th2 hypersensitivity?
atopic eczema
Chronic allergic rhinitis
Chronic asthma
What is Type IV cytotoxic hypersensitivity?
Tissue injury by cytotoxic T cells
Antigen presented to sensitised CD8 T cells
Antigen cell associated cytotoxicity.
- perforin
- granzyme
Give some examples of type IV cytotoxic hypersensitivity?
Graft rejection
Some drug reactions
Onset type I diabetes
In type III hypersensitivity, what does the activation of complement cause?
Inflammation and the attractions of neutrophils
Give and example of type IV Th1 hypersensitivity?
contact dermatitis
