1. Hypersensitivity Reactions Flashcards
What is the main cause of immunosuppression?
Malnutrition >65yrs
Define hypersensitivity.
the antigenspecific immune responses that are either inappropriate or excessive and result in harm to host
What exogenous antigens can cause hypersensitivity reactions? (3)
- Non infectious substances (innocuous) - allergies like pollen
- Infectious microbes
- Drugs (Penicillin)
What can cause hypersensitivity reactions to intrinsic antigens?
- Infectious microbes (mimicry)
- Self antigens (auto-immunity)
What is mimicry?
Hosts attacks itself due to structural similarities between microbe and host
WHat are the different types of hypersensitivity reactions?
- Type I or immediate (Allergy)
- Type II or antiBody mediated/ cytotoxic - tissue specific
- Type III or immune Complexes mediated
- Type IV or cell mediated(Delayed)
which of the types if hypersensitivities are antibody mediated and which antibody ?
type I -IgE
type II - IgG
type III - IgG
what is the difference between the antigen of type I and IV?
type I - Environmental non infectious antigens
type II - Environmental infectious agents and self antigens
hat is the sensitisation phase of hypersensitivity?
First encounter with the antigen. Activation of APCs and memory effector cells. A previously exposed individual to the antigen is said to be “sensitized”
What is the effector phase?
Pathologic reaction upon re-exposure to the same antigen and activation of the memory cells of the adaptive immunity
in which phase are the clinical manifestations of hypersensitivity present?
effector phase
How long does type II hypersensitivity reactions take to develop?
Usually develops within 5-12 hr
Which antibodies do type II hypersensitivity reactions involve?
IgG or IgM antibodies
What antigens are targeted in type II hypersensitivity reactions? give examples.
Targets cell bound antigens:
• Exogenous: Blood group antigens, Rhesus D antigens
• Endogenous: self antigens
What are the different outcomes of type II reactions?
- Tissue/cell damage
* Physiological change
What 2 mechanism in type II reactions cause tissue/cell damage after the antibody binds to antigen?
- complement activation
- antibody-dependent cell cytotoxicity (Natural Killer cells)
What is involved in the complement system in type II reactions?
- Cell lysis (MAC, membrane attack complex) - influx of fluid
- Neutrophil recruitment/ activation (C3a/C5a) - Fc receptors of neutrophils bind to antibodies on cell
- Opsonisation (C3b) -m
Give examples of type II reactions involving complement activation. (2)
- Haemolytic disease of the newborn (HDN) - Antigen = Rhesus D
- Transfusion reactions - Antigen= ABO system
explain antibody-dependent cell cytotoxicity (NK cells)
natural killer cells can recognise (using Fc receptors) and kill antibody coated target cells that express pathogen antigens on their surface.
perforins –> cell lysis
granzymes –> apoptosis
Give examples of type II reactions involving Antibody-dependent cell cytotoxicity. (3)
- Autoimmune haemolytic anaemia (warm and cold)
- Immune thrombocytopenia Purpura
- Goodpasture’s syndrome (anti-GBM)
what is Goodpasture’s syndrome
- autoimmune disease in which antibodies attack the basement membrane in lungs and kidneys
- attack the alpha-3 subunit of type IV collagen
- binding of antibody to alpha 3 chain activates complement systems leading to chemoattraction of neutrophils which release ROS that damages the basement membrane
why are the lungs and kidney most affected by Goodpasture’s syndrome and how does it present?
toxins cause damage to collagen chain, exposing the antigens if alpha 3 chain. lungs and kidneys receive the most toxins through inhalation and filtrations
lungs (alveoli)- cough, haemoptysis, restrictive lung disease
kidneys (glomeruli)- haematuria, proteinuria, nephritic syndrome
What is the importance of complement pathway in type II reactions?
Its involved in the innate immune response, adaptive immune response as well as the disposal of unwanted substances within the body.
What is haemolytic transfusion reaction, what can it cause?
RBCs given in transfusion are destroyed by hosts immune system (IgM)
- Shock, kidney failure, circulatory collapse, and death
What is the immune mechanism underlying heamolytic transfusion reaction?
- Incompatibility in the ABO or rhesus D antigens
- Donor RBC destroyed by recipient’s immune system
- RBC lysis induced by type II hypersensitivity involving by the naturally occurring antibodies (IgM)
what are the major blood groups and their antigens?
- blood group A – has A antigens on the red blood cells • blood group B – has B antigens
- blood group O – has no AB antigens
- blood group AB – has both A and B antigens
what antibodies do each of the major blood groups have?
- blood group A subjects – have anti-B antibodies in the plasma
- blood group B subjects – have anti-A antibodies in the plasma
- blood group O subjects – have both anti-A and anti-B antibodies in the plasma blood group
- AB subjects – have NO antibodies in the plasma
what is the rule for blood transfusions?
the donated RBCs must lack the same ABO that the recipient’s red blood cells lack.
which blood groups are universal blood donors and universal plasma donors and why?
group O individuals lack any A or B antigens on their red cells, they are considered universal blood donors.
Group AB individuals are universal plasma donors, as they lack AB antibodies
What is the mechanism behind haemolytic disease of the newborn?
- Rh+ father
- Rh- mother carrying first Rh+ fetus. Rh antigens from the developing fetus can enter the mother’s blood during delivery.
- In response to the fetal Rh antigens, the mother will produce anti-Rh antobodies
- If the woman becomes pregnant with another Rh+ fetus, her anti-Rh antibodies will cross the placenta and damage fetal RBCs
which antigen is found in Rh+ individuals
Rh-positive blood denotes the presence of the D antigen on the red cells of an individual’s blood.
What is the treatment to prevent HDN?
Rh-negative pregnant women are given a small amount of Rh immunoglobulin (anti-D), RhoGAM, which prevents their own formation of anti- D antibodies. - It does this by binding to the antigens in the mothers blood and preventing them from coming into contact with the mothers immune system.
The aim of this is to prevent initial sensitisation of the mother.