Food allergy Flashcards
Examples of non-immunological adverse reactions to foods - enzyme deficiency
Enzyme deficiency
- Lactase deficiency(inherited/acquired)
- Alcohol dehydrogenase deficiency
Examples of non-immunological adverse reactions to foods - histamine reactions
- Strawberries, salami, tuna, salmon
Examples of non-immunological adverse reactions to foods - toxic
- Scrombotoxin poisoning
Other examples of non-immunological adverse reactions to foods
- Food-sensitive migraine
- Flushing in acne rosacea
Food intolerances - WHO classification
- Now classified by WHO to include all ‘detrimental reactions to food that are non-IgE mediated’
Early phase allergic reaction
- 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
Events that follow mast cell IgE ligation
- 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
Pharmacological effects of mast cell mediators
Skin/mucus membranes - wheal and flare (hives) and swelling(angioedema)
Nose(discharge, sneezing etc)
Eyes(conjunctivitis)
Gut(oral allergy, vomiting, diarrhoea)
Lung(wheeze)
GI symptoms of IgE-mediated food allergy
- Oral allergy(itching, tingling, irritation)
- Nausea, vomiting, diarrhoea(but rarely alone)
Cutaneous symptoms of IgE-mediated food allergy
- Hives, angioedema
Resp symptoms of IgE-mediated food allergy
- Upper and lower airway symptoms
Cardio symptoms of IgE-mediated food allergy
- Dizziness, collapse due to hypotension
Symptoms of IgE-mediated food allergy - general features
- Follows exposure rapidly (usually minutes)
- Generally multi-system
- Recedes rapidly
- Reproducible
- Multiple food sources implicated only rarely
Detection of allergen-specific IgE in vivo - skin testing
- 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
Principle of allergen-specific IgE immunoassay
- 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…’’
Features of skin prick test
- 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
Features of serology testing
- 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
Pitfalls of food allergy testing
- 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
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
Most common food allergy amongst UK adults
Birch oral allergy syndrome
Features of birch oral allergy syndrome
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
Does birch oral allergy syndrome progress to anaphylaxis
No
Birch pollen sensitisation
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)
