Food allergy

Question 1

Examples of non-immunological adverse reactions to foods - enzyme deficiency

Answer 1

Enzyme deficiency

• Lactase deficiency(inherited/acquired)
• Alcohol dehydrogenase deficiency

Question 2

Examples of non-immunological adverse reactions to foods - histamine reactions

Answer 2

• Strawberries, salami, tuna, salmon

Question 3

Examples of non-immunological adverse reactions to foods - toxic

Answer 3

• Scrombotoxin poisoning

Question 4

Other examples of non-immunological adverse reactions to foods

Answer 4

• Food-sensitive migraine

- Flushing in acne rosacea

Question 5

Food intolerances - WHO classification

Answer 5

• Now classified by WHO to include all ‘detrimental reactions to food that are non-IgE mediated’

Question 6

Early phase allergic reaction

Answer 6

• In allergic individuals, exposure to allergens leads to the rapid development of symptoms
• This reaction develops within seconds or minutes of exposure and results from the binding of allergens to pre-formed igE antibodies on the surface of mast cells and basophils

Question 7

Events that follow mast cell IgE ligation

Answer 7

• IgE binds its specific allergen
• Cross-linking of IgE antibodies by allergen leads to clustering of FcepsilonR1 receptors
• The intracellular portion of the receptor becomes phosphorylated
• The resulting intracellular cascade leads to cellular activation
• Mast cell ‘degranulates’ releasing histamine, tryptase and other pre-formed mediators

Question 8

Pharmacological effects of mast cell mediators

Answer 8

Skin/mucus membranes - wheal and flare (hives) and swelling(angioedema)

Nose(discharge, sneezing etc)

Eyes(conjunctivitis)

Gut(oral allergy, vomiting, diarrhoea)

Lung(wheeze)

Question 9

GI symptoms of IgE-mediated food allergy

Answer 9

• Oral allergy(itching, tingling, irritation)

- Nausea, vomiting, diarrhoea(but rarely alone)

Question 10

Cutaneous symptoms of IgE-mediated food allergy

Answer 10

• Hives, angioedema

Question 11

Resp symptoms of IgE-mediated food allergy

Answer 11

• Upper and lower airway symptoms

Question 12

Cardio symptoms of IgE-mediated food allergy

Answer 12

• Dizziness, collapse due to hypotension

Question 13

Symptoms of IgE-mediated food allergy - general features

Answer 13

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

Question 14

Detection of allergen-specific IgE in vivo - skin testing

Answer 14

• Allergen extracts applied as drops
• Top layers of epidermis punctured with lancet, allowing the allergen to contact cutaneous mast cells
• If mast cell are sensitised to the allergen, degranulation produces an itchy wheal and flare response within 15 mins
• Positive and negative controls required for validation

Question 15

Principle of allergen-specific IgE immunoassay

Answer 15

• Still commonly referred to as RAST tests, but no longer performed with radio-isotopes
• Send a clotted sample to your immunology lab asking for “specific IgE to…’’

Question 16

Features of skin prick test

Answer 16

• Requires clinic infrastructure - not easily available to all users
• Quick results
• Smaller range of allergens available
• Affected by medication
• Need normal skin for testing
• Single vs multiple tests cost similar
• Operator-dependent
• Multiple tests = multiple punctures

Question 17

Features of serology testing

Answer 17

• Available to all users via lab
• Turnaround days to weeks
• > 600 individual allergens available
• Unaffected by medication
• Unaffected by skin conditions
• Multiple tests expensive
• Multiple tests can be performed from single sample
• Lab-dependent

Question 18

Pitfalls of food allergy testing

Answer 18

• Native allergens used for testing are natural products and contain a mix of different allergens; the test result reflects a composite of IgE directed against these molecules
• Sensitisation to different molecules produces different risk profiles and sometimes false positive or negative results

Question 19

Primary allergens

Answer 19

• Unique to allergen source
• Sensitisation = risk of severe reactions
• Don’t produce false-positives for other allergens
• Positive by serology and skin test

Question 20

Pan-allergens

Answer 20

• Found in multiple allergen sources
• Usually milder reactions or no reactions
• Skin tests less sensitive compared to serology

Question 21

Most common food allergy amongst UK adults

Answer 21

Birch oral allergy syndrome

Question 22

Features of birch oral allergy syndrome

Answer 22

IgE directed against major birch pollen allergen (Bet v 1) cross-reacts with homologous proteins in plant-derived foods (eg Ara h 8)
Oral itching upon exposure to raw fruit, nuts and vegetables

Question 23

Does birch oral allergy syndrome progress to anaphylaxis

Answer 23

No

Question 24

Birch pollen sensitisation

Answer 24

Patients who are sensitised to birch pollen often sensitised to nuts and fruits by serology – but don’t always have symptoms (false positive)
Patients with birch oral allergy syndrome typically skin test negative despite allergy (false negative)