Allergy

Question 1

What is the definition of hypersensitivity?

Answer 1

An immune response that causes collateral damage to self

Question 2

What cell or antibody mediates Type I Hypersensitivity?

Answer 2

IgE

Question 3

What cell or antibody mediates Type II Hypersensitivity?

Answer 3

IgG (mediates Cytotoxic hypersensitivity)

Question 4

What cell or antibody mediates Type III Hypersensitivity?

Answer 4

Immune complex

antigen-antibody complex

Question 5

What mediates Type IV Hypersensitivity?

Answer 5

Cell-mediated

TH1 cells release cytokines to activate macrophages and Tc cells which cause direct cellular damage

Question 6

How does IgE cause Type I Hypersensitivity?

Answer 6

• Antigen induces crosslinking of IgE bound to mast cells and basophils
• causes degranulation and releases vasoactive mediators

Question 7

How does IgG cause Type II Hypersensitivity?

Answer 7

• Anitbody is directed against antigens on cell

- cell is destructed by either complement activation or ADCC

Question 8

What is ADCC?

Answer 8

Antibody-dependent cell-mediated cytotoxicity

Question 9

How does the immune complex cause Type III Hypersensitivity?

Answer 9

• complex is deposited in various tissues
• complement activation
• massive neutrophil migration

Question 10

Give an example of a typical manifestation of a Type I Hypersensitivity reaction?

Answer 10

• Anaphylaxis
• Local anaphylaxis
  e. g. hay fever, asthma, eczema, hives, food allergy

Question 11

Give an example of a typical manifestation of a Type II Hypersensitivity reaction?

Answer 11

• blood transfusion reaction

- autoimmune haemolytic anaemia

Question 12

Give an example of a typical manifestation of a Type III Hypersensitivity reaction?

Answer 12

• Localised e.g. Arthus reaction

- Generalised e.g. necrotising vasculitis, rheumatoid arthritis, Systemic lupus erythematosus

Question 13

Give an example of a typical manifestation of a Type IV Hypersensitivity reaction?

Answer 13

• Contact dermatitis
• Graft rejection
• Tubercular lesions

Question 14

What causes an allergy?

Answer 14

An allergen

Question 15

What is the “hygiene hypothesis”?

Answer 15

The thought that developing countries have less allergies as they are more exposed to an allergic environment.

Developed countries have higher levels of antibiotic use and better sanitation => develop more allergies.

Question 16

How long after exposure does a Type I reaction occur?

Answer 16

Immediate reaction - occurs within minutes and up to 2 hours after exposure to allergen

Question 17

What routes of exposure can provoke a Type I reaction?

Answer 17

skin contact
inhalation
ingestion
injection

Question 18

Will a patient react the same way with every exposure to the allergen that provoked a Type I reaction?

Answer 18

Yes

reaction is consistent with every exposure

Question 19

Give examples of Type I allergens which can be ingested

Answer 19

Nuts

Seafood

Question 20

Give examples of Type I allergens which can be inhaled

Answer 20

Pollen

House dust mite

Question 21

Give examples of Type I allergens which come into contact with the skin

Answer 21

Latex

Animal Dander

Question 22

Give examples of Type I allergens which can be injected

Answer 22

Bee/wasp sting

Medication

Question 23

How does Urticaria usually present clinically?

Answer 23

• Very itchy
• Lesions appear within 1 hour
• Lasts 2-6 hours, sometimes 24 hours

“hives”, “wheals”, “nettle rash”

Question 24

How does angioedema usually present clinically?

Answer 24

• Localised swelling of subcutaneous tissue or mucous membranes
• Non pitting oedema
• Not itchy

Question 25

What investigations can be done in the case of a Type I reaction?

Answer 25

- Specific IgE - Skin prick or prick-prick testing - Challenge test (only if SPT negative) - Serum mast cell tryptase level (during anaphylaxis)

Question 26

What is the risk of anaphylaxis during skin prick tests?

Answer 26

1:3000

Question 27

What medication can be used to manage Type I allergic reactions?

Answer 27

- Anti-histamines Prevent effects of mast cell activation - Corticosteroids Anti-inflammatory - Adrenaline auto injector (for anaphylaxis) - Sodium Cromoglycate mast cell stabilisers => block mast cell activation

Question 28

Aside from medication, what other forms of management are there for Type I allergic reactions?

Answer 28

- Allergen avoidance - Immunotherapy - Medic Alert bracelet - Information and Education

Question 29

What strength of adrenaline auto-injector should be prescribed for adults and for children?

Answer 29

300µg adults | 150µg children

Question 30

How long after exposure does a Type IV reaction occur?

Answer 30

24-48 hrs

Question 31

Give examples of Type IV allergens which come into direct contact with the skin

Answer 31

preservatives in cosmetics rubber accelerators

Question 32

Give examples of Type IV allergens which are responsible for airbourne contact

Answer 32

fragrances | plants

Question 33

Give examples of a Type IV allergen which is injected

Answer 33

Tattoo

Question 34

What are the chambers on patch testing called and where are they applied?

Answer 34

Finn chambers | applied on the back

Question 35

When are the patch tests removed and when are the readings taken?

Answer 35

Removed after 48 hours | Readings at 48 and 96 hours

Question 36

Other than allergy, what can be the cause of dermatitis?

Answer 36

Endogenous | Irritant

Question 37

What is irritant contact dermatitis?

Answer 37

- Non-immunological process - Pattern depends on exposure - Contact with agents that irritate skin directly

Question 38

Give an example of an endogenous form of dermatitis?

Answer 38

Atopic eczema - Dry skin and flexural - Often associated with asthma and hayfever