1. Hypersensitivity Reactions Flashcards
Define the term hypersensitivity
The antigen-specific immune responses that are either inappropriate or excessive and result in harm to the host.
Hypersensitivity can be caused by exogenous antigens. Give 2 types of these.
Non-infectious substances.
Infectious microbes.
Drugs.
Hypersensitivity can be caused by intrinsic antigens. Give 2 types of these.
Infectious microbes.
Self antigens.
What is the sensitisation phase?
A persons first encounter with the antigen. Activation of antigen presenting cells and memory effector cells. Once exposed, individual is sensitised.
What is the effector phase?
A pathological reaction upon re-exposure to the same antigen and activation of the memory cells of the adaptive immunity. Is the clinical manifestation of the hypersensitivity reaction.
How long does a Type II hypersensitivity reaction take to develop?
5-12 hours
What antibodies are involved in a type II hypersensitivity reaction?
IgG or IgM.
What type of antigens does a Type II hypersensitivity reaction target?
Cell bound antigens (both exogenous and intrinsic).
What two types of damage can type II hypersensitivity reactions induce?
Tissue/cell damage or physiological change.
Describe the mechanism by which tissue/cell damage is causes in a Type II hypersensitivity reaction
Complement activation, cell lysis, opsonisation, neutrophil recruitment and activation.
Also by ab-dependent cell cytotoxicity.
Give one example of a type II hypersensitivity reaction caused by an exogenous antigen
Haemolytic disease of the newborn (rhesus D). Transfusion reactions (A/B antigens).
Give one example of a type II sensitivity reaction caused by an intrinsic antigen
Autoimmune haemolytic anaemia.
Immune thrombocytopenia Purpura.
Goodpasture’s syndrome.
A haemolytic transfusion reaction is a life-threatening condition caused by a type II sensitivity reaction involving IgM. What is the mechanism for this reaction?
Incompatibility in the ABO group or rhesus D antigens. So donor RBC’s are destroyed by the recipient’s immune system.
Haemolytic disease of the newborn is an example of a disease caused by a type II hypersensitivity reaction to IgG. What is the mechanism of this reaction?
Rh+ father and Rh- mother produce Rh+ foetus. In first pregnancy, antigens from developing foetus enter the moths blood during delivery and mother becomes sensitised. If the women has another pregnancy with a Rh+ foetus, her anti-Rh antibodies cross the placenta and damage feral red blood cells.
What is given to known Rh- mothers during pregnancy to prevent the mother becoming sensitised?
IgG anti-RhD - kills foetal Rh antigens.
By what 2 mechanisms can a type II hypersensitivity reaction cause physiological change?
Receptor stimulation.
Receptor blockade.
By what mechanism is Grave’s disease a type II hypersensitivity reaction? What is the antigen?
Receptor stimulation increases thyroid activity. Antigen is TSH receptor.
By what mechanism is myasthenia gravis a type II hypersensitivity reaction? What is the antigen?
Receptor blockade leads to impaired neuromuscular signalling. Antigen is acetylcholine receptor.
Give one therapeutic approach to treating type II hypersensitivity reactions causing tissue damage.
Immune suppression to prevent complement activation.
Plasmapheresis to remove circulating antibodies and inflammatory mediators.
Splenectomy to reduce opsonisation and phagocytosis.
Intravenous immunoglobulin to cause IgG degradation.
Give one therapeutic method of treating type II hypersensitivity reactions causing physiological change
Correct metabolism to reduce receptor stimulation.
Use replacement therapy to fix a receptor blockade.
Within what time frame does a type III hypersensitivity reaction normally develop?
3-8 hours
What antibodies are involved in a type III hypersensitivity reaction?
IgM or IgG.
What type of antigens does a Type III hypersensitivity reaction target?
Soluble antigens - both foreign and endogenous.
What type of hypersensitivity reaction causes tissue damage by immune complex deposition?
Type III
