Lecture 3 - Food Allergy Flashcards
What is the definition of a food allergy?
Adverse reaction to food that involves the immune system
What are the 2 main categories of food allergy?
IgE mediated
Non-IgE mediated
What are some examples of IgE mediated food allergies?
Anaphylaxis
Urticaria
Angioedema
Acute rhinitis
What are some examples of non-IgE mediated food allergies?
Contact dermatitis
Celiac disease
Heiners syndrome
FPIES
What is the broad process for which allergies occurs?
Sensitisation stage
Reaction stage
What is the dual allergen hypothesis for alleries occurring?
The way at which a patient is exposed to an antigen makes it more likely for an allergic repsonse to develop
Skin = likely allergy
Tolerance = GI exposure
What T helper cell usually leads to the development of allergies?
T Helper 2
Which T Helper cells usually are involved in cutaneous exposure vs oral /GI exposure?
Cutaneous = TH2 memory/allergy
Oral/GI = TH1 tolerance
What is the allergy mechanism for IgE mediated and non IgE mediated?
Sensitisation stage:
What IL are made?
Dendritic cells pick up allergen
MHC II presents to T Helper 2 cells
TH2 produce IL-4, IL-13 and IL-4 and IL-13 convert IgM to IgE (Class switching)
IgE binds to mast cells priming them
What happens once the allergen is reintroduced into the body?
Allergen binds to IgE on primed mast cell
Mast cell degranulates
TH2 cells proliferate making more IL-4, IL-13 and IL-5
IL-5 makes eosinophils migrate to the area
What activates mast cells following reintroduction of the allergen?
Minimum of 2 membrane bound IgE need to be cross linked by the antigen
Leading to degranulation
What do IL-4 and IL-13 and do?
Stimulate the class change of IgM to IgG
What is the function of IL-5?
Stimulates Eosinophil migration
What are some substances released by the degranulation of mast cells?
Histamine
Prostaglandins
Tryptase
Leukotrienes
IL-4 + IL-13
IL-5
What is the function of histamine?
Vasodilation
Vasopermeabilty
Bronchoconstriction
Mucus
What is the function of prostaglandins ?
Bronchoconstriction
What is the function of non IL-4 and 13?
Switch B lymphocytes to IgE
What are the functions of leukotrienes?
Bronchoconstriction
Mucus
What is tryptase good for measuring?
What’s it bad for measuring?
Good for drug allergy
Bad for food allergy
What are the main foods with allergens?
Wheat
Nuts
Soy
Shellfish
Kiwis
Milk
Eggs
Fish
What are the 4 main causes of non-IgE mediated food allergies?
Milk
Soy
Wheat
Eggs
What is the mnemonic used to take an allergen history?
EATERS
What does EATERS stand for when taking an allergen history?
Exposure
Allergen
Timing
Environment
Reproducibility (symptoms can always be triggered)
Symptoms
When do symptoms manifest in a patient with IgE mediated allergies?
Symptoms occur rapidly (within 2hrs of exposure)
What are the red flag features of IgE mediated allergies?
Anaphylaxis (ABC symptoms)
What is the most common type of non IgE mediated allergy?
Milk
Soya
What are some features of non IgE mediated allergy?
Onset of symptom
Normally 1-72hrs after ingestion and normally occurs in less than 1 year olds
What are some typical factors of allergies?
Common allergen
Urticaria
Reproducible
What investigations can be done for food allergies?
sIgE (specific IgE to certain foods)
SPT (Skin prick test)
Challenge (open food challenge, single blinded challenge, double blind challenge)
What is the point of Skin Prick Test (SPT)?
Reflect IgE bound to cutaneous mast cells adn subsequent release of mediators like histamine
What is sIgE (specific IgE)?
Reflects sIgE within the blood
Which can indicate sensitisation not allergy
How do specific IgE diagnostic tests work?
Allergen is absorbed and immobile
Patients serum is added
Allergen bound IgE is detected by enzymatically labelled anti-human IgE monoclonal antibody (brighter it is more there is)
How does the skin prick test work?
Allergens injected into skin and see if a reaction occurs
Histamine injected into skin (control_
Nothing injected as a control too
Look at slide 19, what do you think for the initial diagnosis?
IgE mediated milk allergy since the allergy occurs 5mins after exposure also have urticaria
How do you test to confirm a diagnosis of IgE mediated milk allergy?
Specific IgE to milk
Look at slide 24:
What is the most likely diagnosis?
Not likely to be IgE mediated milk allergy since happens 5hrs after exposure
Urticaria following viral infection
Does a positive specific IgE indicate allergy?
No not always
Can a baby be allergic to cows milk if they are allergic to breast milk?
Yes
Start from slide 25, how do you help diagnose the milk allergy?
How long should this be done for?
Maternal exclusion of all milk products for at least 4 weeks (too see if symptoms improve)
Then after4 weeks give milk again to see if it worsens
Slide 32, case 3, should egg be excluded as the cause of the allergy?
No since a positive result does not indicate an egg allergy
What is angiodema?
Swelling of the deep tissues in the body (deeper than the skin)
Page 36, what is the likely cause of allergens?
Peanut
What do high levels of specific IgE mean?
Increased risk of allergy not the severity
What is pollen food syndrome?
Where foods like raw apple are similar to birch pollen, birch pollen IgE attach to the apple protein
What are some symptoms pollen food syndrome?
Raw apples (mild lip swelling, itchy tongue, uncomfortable throat))
Why does pollen food syndrome barely happen with cooked foods?
The proteins get degraded
What are some nuts causing pollen food syndrome?
Hazelnut
Peanut
Almond
Walnut
Brazil
What are some food allergy managements?
Understand local dietitian services
Manage comorbitides like:
-asthma
-eczema
-Hayfever
How to interpret:
History of acute reaction with clear identifiable trigger + Positive test?
Allergy
How to interpret:
No history/unclear history of exposure/no exposure + Positive test?
Sensitisation
How to interpret:
Eats the food + Positive test?
Sensitisation but tolerant
How to interpret:
Positive sIgE + n reaction to food?
Believe the history and is fine
How to interpret:
Negative sIgE + history of an acute reaction?
Believe the history, allergic
How do you diagnose non IgE allergies?
Complete exclusion for 4 weeks followed by reintroduction
What is FPIES?
(Food Protein Induced Enterocolitis syndrome)?
Non IgE mediated food allergy that typically presents in infancy with repetitive protracted vomiting that begins 1-4hrs after food ingestion
Diarrhoea
Dehydration
Pale, lethargic
No cutaneous and respiratory symptoms
Hypotension, hypothermia and mimic sepsis
When does FPIES present?
Normally in first year of life
What is eczema?
Treatment?
Inflammatory disorders
Steroids to treat
How do we treat eczema?
250-500g emollient
