Type 1 Hypersensitivity

Question 1

What is Atopy?

Answer 1

A genetic tendency to produce IgE to normally innocuous environmental allergens

Question 2

What is an allergy?

Answer 2

Clinical expression of atopic tendency

Question 3

What is type 1 hypersensitivity mediates by?

Answer 3

Inappropriate production of specific IgE antibodies to harmless antigens

Question 4

What do the antigens react with in type 1 hypersensitivity?

Answer 4

The IgE antibodies which are bound to mast cells

Question 5

What happens when the antigen binds to the IgE bound to mast cells?

Answer 5

Degranulation of mast cells

Question 6

What is sensitisation?

Answer 6

This is the initial event that lead to the specific IgE being developed for that allergen

Question 7

What happens in sensitisation?

Answer 7

• CD4 cells recognise the allergen

* They proliferate and differentiate into T Helper 2 cells

Question 8

What do the Th2 cells release?

Answer 8

IL-4, that stimulates the production of IgE by B Cells specific to that allergen

Question 9

What does mast cells degranulation lead to the release of?

Answer 9

Mast cell mediators

Question 10

What are the 2 forms of mast cell mediators?

Answer 10

Pre-formed

Newly synthesised

Question 11

What are some examples of preformed mast cell mediators?

Answer 11

histamine
heparin
tryptase

Question 12

What are some examples of newly synthesised mast cell mediators?

Answer 12

Prostaglandins

Leukotrienes

Question 13

How are allergic reactions described?

Answer 13

Biphasic

Question 14

What does biphasic mean?

Answer 14

Allergic reactions have an early phase and late phase reaction

Question 15

What is responsible for the early phase reaction?

Answer 15

Histamine

Question 16

What does histamine cause?

Answer 16

Vasodilation
Increased vascular permeability
Broncho-constriction
–symptoms of allergy

Question 17

What is responsible for the late phase reaction?

Answer 17

TNF-α

Question 18

What does TNF-α cause?

Answer 18

A localised inflammatory process at the site of exposure.

Question 19

How long can the late phase take?

Answer 19

A few hours

Question 20

What is anaphylaxis?

Answer 20

The most serious type of allergy

Question 21

What happens in an anaphylaxis reaction?

Answer 21

vasodilation and increased vascular permeability.
Shift of fluids from the vascular to the extra-vascular space- fall in vascular tone.
Severe drop in blood pressure.

Question 22

How does anaphylaxis present?

Answer 22

• Low blood pressure
• Angioedema
• Airway obstruction

Question 23

What can cause anaphylaxis?

Answer 23

Foods - fish, shellfish, eggs, milk, wheat, nuts
Insect venoms - bee, wasp
Drugs - antibiotics, anaesthetic agents, antisera

Question 24

What is the management of anaphylaxis?

Answer 24

Epinephrine (adrenaline)

Question 25

How are allergies diagnosed?

Answer 25

History
Skin prick tests
Laboratory investigations: IgE levels (RAST test)

Question 26

What are the possible managements of allergies?

Answer 26

Patient education

- Allergen avoidance
- Antihistamines - local / systemic
- Sodium cromoglycate - local / systemic
- Steroid - local / systemic
- Leukotriene antagonists
- Desensitisation immunotherapy

Question 27

What gene is associated with allergy?

Answer 27

Filaggrin gene

Question 28

What is the hygiene hypothesis?

Answer 28

Increase in allergies in the developed world is caused by reduced exposure to microorganisms in early life.

Question 29

What causes the symptoms in an allergic reaction?

Answer 29

Degranulation of mast cells and the release of mediators

Question 30

When do mast cells initiate the allergic symptoms?

Answer 30

When the IgE and allergen interact

Question 31

How are allergic responses different on repeat exposure?

Answer 31

Tend to get worse on repeat exposures due to increased sensitisation