Type I Hypersensitivity - Allergy

Question 1

What immunoglobulin is involved in Type I hypersensitivity?

Answer 1

IgE

Question 2

Describe type I hypersensitivity reactions

Answer 2

• immediate reaction <30 mins
• local reaction: ingested or inhaled allergen
• systemic reaction: insect sting or IV administration
• mediated by IgE

Question 3

What helper T cell elicits IgE production?

Answer 3

TH2

Question 4

Mechanisms of Type I hypersensitivity

Answer 4

• abnormal adaptive immune response against allergens: TH2 response (IL-4,5,13) > IgE response
• mast cell activation

Question 5

Define type I hypersensitivity

Answer 5

Immediate excessive adaptive immune response to allergens mediated by IgE

Question 6

What is the hygiene hypothesis?

Answer 6

Children exposed to animals, pets + microbes in early postnatal period appears to be protected against certain allergic diseases

Question 7

What is the ‘old friend hypothesis?

Answer 7

Western lifestyle induces alteration of symbiotic relationships with parasites + bacteria leading to dysbiosis of micro biome at mucosal surfaces

Question 8

What is dysbiosis?

Answer 8

Compositional + functional alteration of micro biome

Question 9

Outline the mechanism of allergic reaction

Answer 9

• allergen breaches mucosal barrier
• phagocytosis by dendritic cells
• antigens presented to naive T cells by MHC class II
• plasma cells produce IgE
• IgE binds to mast cells
• mast cell degranulation > histamines, chemokines, leukotrienes + prostaglandins release
• vasodilation, bronchial constriction + increased vascular permeability

Question 10

Location of mast cells

Answer 10

• Most mucosal + epithelial tissues e.g. skin + GI tract
• Connective tissue surround blood cells

Question 11

What is urticaria?
What is it caused by?
What mediators are involved?

Answer 11

• Itchy raised rash
• Caused by mast cell activation within epidermis
• histamine + leukotrienes

Question 12

What is angioedema?
What is it caused by?
What mediators are involved?

Answer 12

• swelling
• caused by mast cell activation in deep dermis or subcutaneous or submucosal tissue
• histamine + bradykinin

Question 13

Signs + symptoms of anaphylaxis

Answer 13

• dyspnoea
• urticaria
• angioedema
• hypotension
• dysphagia
• confusion
• loss of consciousnesses

Question 14

Treatment of type I hypersensitivity reactions due to abnormal adaptation immune response against allergens

Answer 14

• allergen desensitisation (oral immunotherapy)
• omalizumab: anti IgE monoclonal antibody
• mepolizumab: anti-IL5 monoclonal antibody

Question 15

Treatment of Type I hypersensitivity due to mast cell activation

Answer 15

Antihistamines
Corticosteroids
Leukotriene receptor antagonists

Question 16

Define allergen desensitisation

Answer 16

Involves the administration of increasing doses of allergen extracts over period of years, given to patient by infection or tablets sublingual

Question 17

Treatment of anaphylactic shock
How does it work including the receptors involved?

Answer 17

IM adrenaline
- *a1**: reverses peripheral vasodilation > reduces oedema + alleviates hypotension
- B2: reverses bronchoconstriction
- B1: increases force of myocardial contraction
- inhibits mast cell activation

Question 18

What represents the main trigger of clinical manifestation of allergic disorders?

Answer 18

Cross linking of antigen specific IgE

Question 19

Examples of mast cell mediators

Answer 19

Tryptase
Histamine
Leukotrienes
Platelet activating factor