(PM3A) Hypersensitivity

Question 1

What is hypersensitivity and autoimmunity?

Answer 1

(1) Damage caused by adaptive immune mechanisms

(2) No hazard can be identified

Question 2

What is the difference between autoimmunity and hypersensitivity?

Answer 2

The source of the antigen:

• (1) Internal = autoimmunity
• (2) External = hypersensitivity

Effector mechanism:
- Could be antibody type or T lymphocytes/ cells

Question 3

What are the types of antibody in effector mechanisms?

Answer 3

(1) Binding + blocking
(2) Histamine
(3) Phagocytosis

Question 4

How are hypersensitivity reactions classified?

Answer 4

Classification table

Class 1-4

Question 5

How does the mediation of class 1-3 compare to that of 4 in hypersensitivity reactions?

Answer 5

1-3 = B cell mediated

4 = T cell mediated

Question 6

Which class of hypersensitivity is most common?

Answer 6

Class 1

Question 7

What is the effector mechanism for hypersensitivity class 1 reactions?

Answer 7

IgE antibody on mast cells

e.g. hayfever/ asthma/ anaphylaxis

Question 8

What is the effector mechanism for hypersensitivity class 2?

Answer 8

IgM + IgG antibody-mediated cell killing

e.g. mismatched blood transfusion/ haemolytic anaemia of a newborn

Question 9

What is the effector mechanism for hypersensitivity class 3?

Answer 9

IgG antibody immune complexes

e.g. serum sickness/ long-term mAb use

Question 10

What is the effector mechanism for hypersensitivity class 4?

Answer 10

T cells (lymphocytes)

e.g. contact dermatitis

Question 11

What are some triggers of hypersensitivity class 1 responses?

Answer 11

(1) Tree pollen
(2) Grass pollen
(3) Flower pollen
(4) Medicines
(5) Latex
(6) Dust mites
(7) Rodents
(8) Birds
(9) Insect bites

Question 12

Which receptor is present on the outside of mast cells?

Answer 12

IgE

Question 13

What is a sentinel?

Answer 13

Another name for a mast cell

Question 14

What is contained within mast cells?

Answer 14

Histamine granules

Question 15

What triggers histamine release from mast cells?

Answer 15

Parasite antigen recognition

Question 16

What are some common signs and symptoms of a hypersensitivity class 1 response?

Answer 16

(1) Swelling
(2) Sneezing
(3) Vasodilation
(4) Itching
(5) Sudden death

Question 17

Why are mast cells considered antigen specific?

Answer 17

Presence of IgE antibodies on surface

Able to recognise parasitic antigens

Question 18

When are mast cells considered part of adaptive immunity?

Answer 18

When they are coated with IgE

To be able to recognise antigens

Question 19

How is hayfever a hypersensitivity reaction?

Answer 19

(1) Allergen in upper respiratory tract/ eyes

(2) Itching + sneezing

Question 20

How is asthma a hypersensitivity reaction?

Answer 20

(1) Allergen in lower respiratory tract
(2) Causes air vessel constriction
(3) Shortness of breath + wheezing

Question 21

How is anaphylaxis a hypersensitivity reaction?

Answer 21

(1) Triggering of sufficient mast cells at the same time
(2) Causes systemic vasodilation
(3) Catastrophic BP drop
(4) Death

Question 22

How may an antigen of a class 1 hypersensitivity reaction?

Answer 22

(1) Removal of antigen – diaries to log when symptoms occur, e.g. removal of foods from diet/ pet from environment
(2) Skin prick test

Question 23

What is a skin prick test?

Answer 23

(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

Question 24

What is the normal role of IgG and IgM in class 2 hypersensitivity reactions?

Answer 24

Killing pathogens

Question 25

What does 'complement' do?

Answer 25

Punches holes in cell membranes of pathogens

Question 26

How is drug-induced anaemia caused?

Answer 26

(1) Drug attaches to red blood cells (erythrocytes) (2) Antibodies bind to drug (3) Lyses red blood cells (4) Causes anaemia

Question 27

What is an example of a high affinity hapten-type reaction?

Answer 27

Drug-induced anaemia

Question 28

What are some common drugs that cause drug-induced anaemia?

Answer 28

(1) Cephalosporins (2) Penicillin (3) Tetracycline

Question 29

What is the normal role of IgG in class 3 hypersensitivity reactions?

Answer 29

Neutralising bacterial toxins + viruses

Question 30

What is a class 3 hypersensitivity reaction?

Answer 30

Binding of IgG antibodies to bacterial toxins

Question 31

How is antivenom made?

Answer 31

(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

Question 32

What is likely to occur if large concentrations/ continued use of antivenom occurs?

Answer 32

Patient may develop immunity to antivenom (serum sickness) (Production of antibodies) Formation of immune complexes

Question 33

What is serum sickness?

Answer 33

High levels of antibody In response to foreign antibody Systemic inflammatory problems

Question 34

What is a modern alternative to antivenom?

Answer 34

Monoclonal antibodies mAb

Question 35

What type/ class of hypersensitivity is relevant when considering use of monoclonal antibodies?

Answer 35

Type/ class 3 hypersensitivity

Question 36

How is hypersensitivity to antivenoms been largely resolved?

Answer 36

Monoclonal antibodies Fully human rather than from horse

Question 37

How are monoclonal antibodies synthesised?

Answer 37

(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

Question 38

What are some common examples of antigen target for monoclonal antibodies?

Answer 38

(1) Human TNF | (2) Human HER2 receptor

Question 39

What is passive immunisation?

Answer 39

Transfer of antibodies into the body

Question 40

What are some disadvantages of antivenom?

Answer 40

(1) Horse proteins (2) Multiple types of antibody (3) Made in animals

Question 41

What is an example of a class 4 hypersensitivity reaction?

Answer 41

Allergic contact dermatitis

Question 42

What is class 4 hypersensitivity?

Answer 42

T helper cells Trigger inflammation In response to microbial peptides

Question 43

What is delayed-type hypersensitivity?

Answer 43

Type/ class 4 hypersensitivity

Question 44

What is the slowest type/ class of hypersensitivity?

Answer 44

Type/ class 4