(PM3A) Hypersensitivity Flashcards by Nikki Gurung

What is hypersensitivity and autoimmunity?

(1) Damage caused by adaptive immune mechanisms

(2) No hazard can be identified

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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

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What are the types of antibody in effector mechanisms?

(1) Binding + blocking

(2) Histamine

(3) Phagocytosis

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How are hypersensitivity reactions classified?

Classification table

Class 1-4

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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

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Which class of hypersensitivity is most common?

Class 1

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What is the effector for hypersensitivity class 1 reactions?

IgE antibody on mast cells

e.g. hayfever/ asthma/ anaphylaxis

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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

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What is the effector for hypersensitivity class 3?

IgG antibody immune complexes

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

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What is the effector mechanism for hypersensitivity class 4?

T cells (lymphocytes)

e.g. contact dermatitis

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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

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Which receptor is present on the outside of mast cells?

IgE

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What is a sentinel?

Another name for a mast cell

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What is contained within mast cells?

Histamine granules

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What triggers histamine release from mast cells?

Parasite antigen recognition

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

(1) Swelling

(2) Sneezing

(3) Vasodilation

(4) Itching

(5) Sudden death

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Why are mast cells considered antigen specific?

Presence of IgE antibodies on surface

Able to recognise parasitic antigens

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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

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 do ‘complement’ proteins 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? (reaction mechanism)

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