What is an allergen?
Any substance stimulating the production of IgE or a cellular immune response.
Allergens are usually proteins but not always. They can also be carbs.
Define sensitivity.
Normal response to stimulus
Define hypersensitivity
Abnormal strong response to a stimulus
What is sensitisation?
Production of IgE antibodies after repeated exposure to an allergen.
What is allergy?
A hypersensitivity reaction initiated by a specific immunological mechanism, that is IgE-mediated (such as peanut) or non-IgE mediated (such as milk allergy).
What is atopy?
A personal or familial tendency to produce IgE in response to exposure to potential allergens.
What is anaphylaxis?
A serious allergic reaction with bronchial, laryngeal and cardiovascular involvement that is rapid in onset and can cause death.
What is food allergy?
A immunologically medaited adverse reaction to foods.
Presentation of allergic rhinitis or hay fever.
Persisten or recurrent block or runny nose.
Itch and sneezing.
Common symptom triggers of allergic rhinitis.
Grass and tree pollens
House dust mites.
Presentation of allergic conjunctivitis.
Red, swollen, watery and itchy eyes.
Itch is a key symptom to distinguish this form of conjunctivitis from others.
Presentation of allergic asthma.
Wheeze
Cough
Shortness of breath
Tight chest
Presentation of atopic dermatitis/eczema.
Itchy skin with scratching leading to chronic skin changes.
Classifications of urticaria/hives.
Less than 6 weeks = acute
More than 6 weeks = chronic
Most allergen of insect allergy in the UK.
Also give presentation.
Stings from wasps or bees.
Presentation can be mild with a large localised sting reaction characterised by redness, swelling and itch.
Define food allergy.
An adverse health effect arising from a specific immune response that occurs on exposure to a food. The definition encompasses responses that are classified as IgE or non IgE mediated.
Difference between food allergy and food intolerance.
Food intolerance is an adverse response that does not involve an immune response.
Most common food allergies
Milk
Egg
Peanuts
Give examples of food characteristics in food intolerances.
Reactions to pharmacologically active food components or illness in resposne to toxins from microbial contamination or to scromboid fish toxin.
E.g. from eating spoiled fish.
How does host characteristics food intolerance differ to food characteristics?
Host characteristics include metabolic disorders such as lactose intolerance and psychological or neurological responses such as food aversion or rhinorrhoea caused by spicy foods.
IgE mediated food allergic symptoms of the skin.
Pruritus
Erythema
Urticaria
Angioedema of lips, face and eyes
IgE mediated food allergic symptoms of GI.
Angioedema of lips, tongue and palate
Oral pruritus
Colicky abdominal pain
Nausea
Vomiting
Diarrhoea
IgE mediated food allergic symptoms of resp system.
Runny and/or blocked nose
Sneezing
Itchy nose
Croupy cough
Stridor
Breathlessness
Cough
Wheeze
IgE mediated food allergic symptoms of CVS.
Pallor
Drowsy
Hypotension
How does non-IgE mediated symptoms differ?
Usually vague with abdo pain and not clearly associated with food contact due to the delayed presentation.
Can mimic other common GI conditions.
Specific disorders of IgE mediated allergy.
Urticaria/Angioedema
Anaphylaxis
Food-associated exercise induced anaphylaxis
Polled food syndrome
Common food triggers leading to anaphylaxis.
Nuts
Fish
Shellfish
Milk
Egg
What is food-associated exercise induced anaphylaxis?
Food triggers anaphylaxis only if ingestion is followed temporally by exercise.
Specific disorders of non-IgE mediated food allergy.
Proctocolitis
Enterocolitis
Eosinophilic oesophagitis
Food protein induced enterocolitis syndrome (FPIES)
What is the most common food allergy in adults?
Pollen food syndrome
What does heat-stable or heat-labile allergens mean?
Heat-stable allergens will persist if food is cooked/heated.
Heat-labile will not.
This means if you cook a heat-labile food that you are usually allergic to, you won't be after it is cooked.
Give an example of a matrix effect on a food allergen.
Baked milk that is found in processed biscuits has a lower allergenicity and availability to the immune system.
This means it can be used in order to reintroduce milk back in to the diet.
What is cross-reactive food allergens?
Foods are related and this means that if you are allergic to one food, you might be allergic to a similar food as well.
An example is if you are allergic to one nut there is a risk you are allergic to more nuts.
Food allergy screening tests.
Skin prick tests (STPs) of assay of serum specific IgE.
Can be used to test foods for which there are no blood tests available.
Prick-prick tests (prick food first and then prick skin)
Can test for IgE antibodies but that only determines the presence of sensitivity and not allergy.
How to treat food allergies.
If they do not resolve it is usually done by desensitisation to the allergen.
An example of this is to give the patient some crumbles of a biscuit with baked milk. And then gradually step it up until milk is reintroduced and does not give an allergic response.
