Immunity 2: Food Allergy

Question 1

Describe the early phase reacion

Answer 1

• Exposure to allergen
• Rapid development of symptoms
• Results from binding of allergens to pre-formed IgE antibodies on the surface of mast cells and basophils

Question 2

Describe the IgE mediated response

Answer 2

• IgE binds to specific allergen
• Cross-linking of IgE antibodies by allergen leads to clustering of FcεR1 receptors
• ## The intracellular portion of the receptor becomes phosphorylated-Intracellular cascade
• Leads to cellular activation
• Mast cell ‘degranulates’ releasing histamine, tryptase and other pre-formed mediators
• Tests to confirm trigger (skin prick, serology, challenge)

Question 3

What is the underlying process that causes of

pharmacological effects of mast cell mediators?

Answer 3

Histamine causes capillaries to dilate and become leaky

Question 4

Outline general features of IgE mediated food allergy [5]

Answer 4

–Follows exposure rapidly (usually minutes)
–Generally multi-system
–Recedes rapidly
–Reproducible
–Multiple food sources implicated only rarely

Question 5

Outline how skin testing is carried out

Answer 5

• Allergen extracts applied as drops
• Top layer of epidermins punctured with lancet, allowing allergen to contact cutaneous mast cells
• If mast cell sensitised to allergen, degranulation produces and itch wheal and flare response witing 15 mins
• Positive and negative controls required for validation
• Less sensitive than serology

Question 6

Outline the principle of allergen-specific IgE immunoassay

Answer 6

Send a clotted sample to immunology lab

Asking for specific igE …[target allergen]….

Question 7

Outline the difference between primary nut allergy and pan-allergen(secondary) sensitisation, and how this can cause confusion when interpreting results

Answer 7

•Primary allergens
–Unique to allergen source
–Sensitisation = risk of severe reactions
–Don’t produce false-positives for other allergens
–Positive by serology and skin test
•Pan-allergens
–Found in multiple allergen sources
–Usually milder reactions or no reactions
–Skin tests less sensitive compared to serology

Question 8

What are the advantages and disadvanatges of skin prick test

Answer 8

Advantages
- results on same day

Disadvantages

• requires clinic
• affected by medication
• smaller range of allergens
• need normal skin
• multiple punctures
• operator dependent

Question 9

What are the advantages and disadvantges of serology?

Answer 9

Advantages

• available to all users via lab
• > 600 allergens available
• unaffected by medication or skin

Disadvantages
- lab dependent