Week 7 - Allergy

Question 1

What is T1 hypersensitivity?

Answer 1

-Allergic responses in response to environmental non-infectious antigens which occur immediately and are driven by IgE and Th2 cells

Question 2

What is T2 hypersensitivity?

Answer 2

-Antibody mediated response against tissues or cellular components driven by IgG or IgM

Question 3

What is T3 hypersensitivity?

Answer 3

-Immune complex mediated response in which IgG binds to a soluble antigen and immune complexes are deposited into the tissues beginning the immune response

Question 4

What is type 4 hypersensitivity?

Answer 4

-Autoimmune responses

Question 5

What is the difference between T1 and T2-T4 hypersensitivity?

Answer 5

-T2-T4 are in response to environmental infectious agents and self-antigens

Question 6

Describe the phases of hypersensitivity

Answer 6

1) sensitization phase which is clinically silent and is first encounter of the antigen
2) Effector phase where there is a clinical manifestation of re-exposure to the same antigen

Question 7

Explain the mechanism behind allergic reactions which results in impaired lung function

Answer 7

1) 1st exposure to antigen -> antigen specific IgE formed
2) Mast cell with high affinity receptor binds antigen-specific IgE
3) 2nd exposure to antigen -> recognised by IgE on mast cell
4) Triggering or release of granule contents (histamine/chemokine)
5) Also triggers synthesis of new mediators (PGs, leukotrienes)
6) Increased vascular permeability, vasodilation and bronchial contraction in response to mediators
7) Massive fluid loss from ECF decreases blood vol and thus BP
8) Impaired lung function

Question 8

What is urticaria?

Answer 8

-Skin manifestation of allergic reaction due to mast cells in epidermis (wheal and flare)

Question 9

What is angio-oedema? When is it dangerous?

Answer 9

• Swelling of lips, eyes, tongue and upper resp airways due to mast cells deep in the dermis
• Dangerous if swelling of upper airways occurs as can lead to suffication

Question 10

What is anaphylaxis?

Answer 10

-Life threatening systemic reaction to allergen

Question 11

Explain what happens in anaphylaxis to make it different from allergic reaction

Answer 11

-Systemic activation of mast cells leads to hypotension/cardiovascular collapse, genreralised urticaria, angio-oedema and CNS disturbances

Question 12

How do you treat anaphylaxis? Explain how this treatment works

Answer 12

• Immediate intramuscular adrenaline
• Reverses peripheral vasodilation, oedema and alleviates hypotension by binding to a1-adrenoreceptors in BVs and causing vasoconstriction
• Reverses bronchospasm by binding to b2-adrenoreceptor in the lungs causing bronchodilaiton
• Increases cardiac output by binding to b1-adrenoreceptor in the heart and increasing the force of contraction
• Inhibits mast cell activation

Question 13

How are allergies diagnosed?

Answer 13

• Good clinical history
• Blood tests for specific IgE
• Skin prick tests if appropriate

Question 14

What is the management for patients with allergies?

Answer 14

• Education of signs and EPIPEN
• Antihistamines, catecholamines
• Allergen avoidance

Question 15

What is allergen desensitisation?

Answer 15

-Administration of increasing doses of allergen over a period of years

Question 16

Define hypersensiivity

Answer 16

-Antigen-specific immune responses which are either inappropriate or excessive and result in harm to host