Hypersensitivity (allergy and anaphylaxis)

Question 1

Do the innate and adaptive immune systems recognise self antigens?

Answer 1

Innate - recognises PAMPs/abnormal antigens (do not recognise self antigens)
Adaptive - recognises lots of antigens (does recognise self antigens)

Question 2

Define hypersensitivity, allergy and anaphylaxis.

Answer 2

An inappropriate & excessive immunological reaction
to an external antigen due to dysfunctional control of the immune system
Allergy - local reaction
Anaphylaxis - systemic reaction

Question 3

What is the mediator of type 1 hypersensitivity reactions? Give examples

Answer 3

IgE
Hayfever/allergies, asthma, atopic eczema, anaphylaxis
Immediate reaction

Question 4

Describe the mechanism of type 1 hypersensitivity.

Answer 4

Exposure to antigen
B Cell Stimulation by TH2 cells
IgE Production 
Binding to Mast Cells
Repeat exposure to allergen
Mast Cell Stimulation & Degranulation
Immediate reaction

Question 5

What are the clinical features of Type 1 hypersensitivity?

Answer 5

Hay Fever, pruritus (itch), sneezing, Urticaria (rash), Angioedema, Anaphylaxis
Immediate reaction

Question 6

What is the mediator of type IV hypersensitivity reactions? Give examples

Answer 6

T lymphocytes/T cytotoxic 
Slow and specific
Delayed/cell-mediated
Allergic Contact dermatitis
Tuberculin Skin Test

Question 7

What investigations would you do to test for hypersensitivity?

Answer 7

Type 1 - measure blood markers such as tryptase, IgE, eosinophil count
Type 1 and IV - skin prick testing
Positive result = lesion >3mm larger than negative control

Question 8

What are the types of treatments available for hypersensitivity?

Answer 8

Avoidance of allergens
Mast cell stabilisers (prevent degranulation) eye drops/ nasal spray
Anti-histamines (eye drops/tablets)
Steroids (nasal spray/tablets)
Leukotriene receptor antagonists (tablets)
De-sensitisation - allergy immunotherapy

Question 9

What is the treatment for anaphylaxis?

Answer 9

ABC
High flow O2
IV fluids
Adrenaline (500mg) IM
IV chlorphenamine (anti-histamine)
IV hydrocortisone (steroid)
Nebulised salbutamol (bronchodilator)