Allergic Disease L5

Question 1

Define Allergy.

Answer 1

An immune response to a (usually harmless) antigen that has deleterious consequences in a proportion of individuals.

Question 2

Which type of hypersensitivity is an atopic allergy associated with?

Answer 2

Type 1.

Question 3

Describe Atopic allergy.

Answer 3

• Affects 20-30% of the population
• IgE mediated
• Total serum IgE may be raised
• Allergen-specific IgE seen in RAST
• Prick test positive

Question 4

Describe the skin prick test.

Answer 4

• A small drop of allergen solution is placed on the skin
• Pricked through with a lancet
• ‘Wheal and flare’ reaction indicates a positive response
• Read in 15 minutes: can measure diameter of wheal

Question 5

Name the skin prick test controls.

Answer 5

Positive: histamine

Negative: carrier

Question 6

List factors that determine atopic allergy probability.

Answer 6

Age: more common in children

Sex: more common in boys than girls

Family size: less common in
larger families

Smoking
Dietary factors: breast-feeding,
fatty acids

Reduced microbial exposure: more common in developed countries and in towns

Question 7

Describe Asthma.

Answer 7

• Chronic inflammation leads to narrowing of the airways

- Bronchial hyper-reactivity to histamine or non-specific stimuli (cold air, smoke etc)

Question 8

List the common causes of Acute Urticaria (Hives).

4

Answer 8

• Insect bites
• Drugs (e.g. antibiotics)
• Infections
• Some foods

Question 9

What is Urticaria (Hives).

Answer 9

Pale red swellings on the skin.

Question 10

Describe Atopic Dermatitis (allergic eczema).

6

Answer 10

• Frequently found in families with a history of atopy
• Often found in young children
• Associated with mutations of filaggrin (barrier protein)
• Serum IgE levels frequently very high
• Skin eruptions are erythematous (red) and filled with pus
• Th2 cells and eosinophils in infiltrate

Question 11

Describe the symptoms of food allergy.

4

Answer 11

• Oral irritation
• Swelling of lips, tongue, pharynx
• Nausea and vomiting
• Occasionally anaphylaxis

Question 12

Read: Food allergy.

Answer 12

Allergen induced IgE crosslinking in GI tract causes localised smooth muscle contraction and vasodilation
- Vomiting or diarrhoea

Mast cell activation may increase gut permeability
- Allergen can enter bloodstream

Symptoms dependent on site on activation of primed mast cells

• Wheezing can result from activation in lungs
• Atopic urticaria (hives) food allergen carried to skin causing wheal and flare reactions

Question 13

Describe Anaphylactoid reactions.

Answer 13

• Induced by substances that cause mast-cell degranulation either directly or by complement
• Not IgE-mediated: no need for prior sensitization

Question 14

List treatments for symptoms in allergic reaction.

Answer 14

• Anti-histamines
• Corticosteroids
• Bronchodilators (asthma)
• Epinephrine (anaphylaxis)

Question 15

Describe Desensitisation.

Answer 15

• A form of immunotherapy
• Patient is given allergen repeatedly in very small doses which gradually increase
• Can be sub-cutaneous (used for allergies to inhaled allergens) or oral (for food allergens)
• Patients respond with decreased production of allergen-specific IgE and increased production of allergen-specific IgG4
• May see changes in cytokine production reflecting induction of Treg response

Question 16

Describe the mechanism of Xolair (allergy drug).

Answer 16

Xolair binds Fc region of IgE and prevent it binding to FceR on mast cells.