Session 1 Flashcards
Define the term hypersensitivity
Antigen-specific immune responses that are either inappropriate or excessive and result in harm to host.
What is the main mechanism behind hypersensitivity reactions?
The mechanisms are the same as those employed by the host to fight infections.
What are the different types of triggers that can lead to hypersensitivity reactions?
Exogenous antigens and intrinsic antigens
Give some examples of exogenous antigens
- Non infectious substances e.g. allergen
- Infectious microbes e.g. hep B
- Drugs e.g. penicillin
Give some examples of intrinsic antigens
- Infectious microbes (microbes)
- Self antigens (auto-immunity)
How many different types of hypersensitivity reactions are there?
4 types
What are the two phases of hypersensitivity reactions?
Sensitisation phase and effector phase
What is the sensitisation phase?
First encounter with the antigen. Activation of APCs and memory effector cells.
What is the effector phase?
Pathologic reaction upon re-exposure to the same antigen and activation of the memory cells of the adaptive immunity
Is it possible to have a hypersensitivity reaction with only one exposure to the antigen?
No
What is it meant if a person is sensitised?
A previously exposed individual is said to be sensitised.
Which antibodies are involved in type II hypersensitivity?
IgG or IgM
After the second encounter with the antigen, how long until the type II hypersensitivity reaction kicks in?
Within 5 - 12 hours
What are the different outcomes of the type II hypersensitivity?
Tissue/cell damage or physiological change
How does type II hypersensitivity lead to tissue/cell damage?
- Complement activation
- ADCC
What type of hypersensitivity reaction is responsible for haemolytic disease of the newborn?
Type II hypersensitivity
What is the antigen response for the hypersensitivity reaction involved in HDN?
Rhesus D
Give an example of disease caused by type II hypersensitivity (IgM)
Haemolytic transfusion reaction
What is the immune mechanism for the haemolytic transfusion reaction?
Incompatibility in the ABO group or rhesus B antigens. Donor RBD destroyed by recipient’s immune system. RBC lysis induced by type II hypersensitivity involving by the natural occurring antibodies (IgM)
Why might the fact that a father is Rh+ and a mother Rh- cause a hypersensitivity reaction and therefore cause issues for the baby?
No issue during the first pregnancy. However, during the second, if she has another Rh+ fetus, her anti-Rh antibodies will cross the placenta and damage fetal red blood cells.
What is the mechanism by which hypersensitivity type II causes physiological change?
Receptor stimulation or receptor blockade
What are some therapeutic approaches to treating tissue/cell damage caused by type II hypersensitivity reaction?
- Immune suppression
- Plasmapheresis
- Splenectomy
- Intravenous immunoglobulin
How does plasmapheriss work?
This removes all the plasma which contains the antibodies. The plasma is then replaced, so the patient now has new plasma that does;t have the antibodies
What sort of effect does plasmapheresis have on the patient?
Short term relief and allows healing of damaged tissue
