(PM3A) Hypersensitivity Flashcards
What is hypersensitivity and autoimmunity?
(1) Damage caused by adaptive immune mechanisms
(2) No hazard can be identified
What is the difference between autoimmunity and hypersensitivity?
The source of the antigen:
- (1) Internal = autoimmunity
- (2) External = hypersensitivity
Effector mechanism:
- Could be antibody type or T lymphocytes/ cells
What are the types of antibody in effector mechanisms?
(1) Binding + blocking
(2) Histamine
(3) Phagocytosis
How are hypersensitivity reactions classified?
Classification table
Class 1-4
How does the mediation of class 1-3 compare to that of 4 in hypersensitivity reactions?
1-3 = B cell mediated
4 = T cell mediated
Which class of hypersensitivity is most common?
Class 1
What is the effector mechanism for hypersensitivity class 1 reactions?
IgE antibody on mast cells
e.g. hayfever/ asthma/ anaphylaxis
What is the effector mechanism for hypersensitivity class 2?
IgM + IgG antibody-mediated cell killing
e.g. mismatched blood transfusion/ haemolytic anaemia of a newborn
What is the effector mechanism for hypersensitivity class 3?
IgG antibody immune complexes
e.g. serum sickness/ long-term mAb use
What is the effector mechanism for hypersensitivity class 4?
T cells (lymphocytes)
e.g. contact dermatitis
What are some triggers of hypersensitivity class 1 responses?
(1) Tree pollen
(2) Grass pollen
(3) Flower pollen
(4) Medicines
(5) Latex
(6) Dust mites
(7) Rodents
(8) Birds
(9) Insect bites
Which receptor is present on the outside of mast cells?
IgE
What is a sentinel?
Another name for a mast cell
What is contained within mast cells?
Histamine granules
What triggers histamine release from mast cells?
Parasite antigen recognition
What are some common signs and symptoms of a hypersensitivity class 1 response?
(1) Swelling
(2) Sneezing
(3) Vasodilation
(4) Itching
(5) Sudden death
Why are mast cells considered antigen specific?
Presence of IgE antibodies on surface
Able to recognise parasitic antigens
When are mast cells considered part of adaptive immunity?
When they are coated with IgE
To be able to recognise antigens
How is hayfever a hypersensitivity reaction?
(1) Allergen in upper respiratory tract/ eyes
(2) Itching + sneezing
How is asthma a hypersensitivity reaction?
(1) Allergen in lower respiratory tract
(2) Causes air vessel constriction
(3) Shortness of breath + wheezing
How is anaphylaxis a hypersensitivity reaction?
(1) Triggering of sufficient mast cells at the same time
(2) Causes systemic vasodilation
(3) Catastrophic BP drop
(4) Death
How may an antigen of a class 1 hypersensitivity reaction?
(1) Removal of antigen – diaries to log when symptoms occur, e.g. removal of foods from diet/ pet from environment
(2) Skin prick test
What is a skin prick test?
(1) Drop of liquid purified antigen on skin
(2) Introduce a tiny prick
(3) Small enough to only let a small amount in for a local effect
(4) Must have adrenaline present in case of allergic reaction
What is the normal role of IgG and IgM in class 2 hypersensitivity reactions?
Killing pathogens
What does ‘complement’ do?
Punches holes in cell membranes of pathogens
How is drug-induced anaemia caused?
(1) Drug attaches to red blood cells (erythrocytes)
(2) Antibodies bind to drug
(3) Lyses red blood cells
(4) Causes anaemia
What is an example of a high affinity hapten-type reaction?
Drug-induced anaemia
What are some common drugs that cause drug-induced anaemia?
(1) Cephalosporins
(2) Penicillin
(3) Tetracycline
What is the normal role of IgG in class 3 hypersensitivity reactions?
Neutralising bacterial toxins + viruses
What is a class 3 hypersensitivity reaction?
Binding of IgG antibodies to bacterial toxins
How is antivenom made?
(1) Venom taken from snake
(2) Injected into horses
(3) Serum taken from horse is the ‘antivenom’
(4) Can be infused into patient following snakebite
- IF type of snake is known
What is likely to occur if large concentrations/ continued use of antivenom occurs?
Patient may develop immunity to antivenom (serum sickness)
(Production of antibodies)
Formation of immune complexes
What is serum sickness?
High levels of antibody
In response to foreign antibody
Systemic inflammatory problems
What is a modern alternative to antivenom?
Monoclonal antibodies
mAb
What type/ class of hypersensitivity is relevant when considering use of monoclonal antibodies?
Type/ class 3 hypersensitivity
How is hypersensitivity to antivenoms been largely resolved?
Monoclonal antibodies
Fully human rather than from horse
How are monoclonal antibodies synthesised?
(1) Isolation of DNA of a single antibody molecule from millions of B cells
(2) Use of machinery (bioreactor) to upscale production
(3) Injection of pure antibody
What are some common examples of antigen target for monoclonal antibodies?
(1) Human TNF
(2) Human HER2 receptor
What is passive immunisation?
Transfer of antibodies into the body
What are some disadvantages of antivenom?
(1) Horse proteins
(2) Multiple types of antibody
(3) Made in animals
What is an example of a class 4 hypersensitivity reaction?
Allergic contact dermatitis
What is class 4 hypersensitivity?
T helper cells
Trigger inflammation
In response to microbial peptides
What is delayed-type hypersensitivity?
Type/ class 4 hypersensitivity
What is the slowest type/ class of hypersensitivity?
Type/ class 4
