Immunology - Allergy Flashcards
What is the difference in CD4 T cell response between microbial recognition and allergen recognition?
Microbe: PAMP is recognised –> Th1 and Th17 response
Allergen/Helminth/Worms: functional change is recognised (eg tissue damage) –> Th2 response
How does Th2 activation cause mast cell degranulation?
Th2 secretes IL4
IL4 activates B cells to produce IgE
IgE causes mast cells to degranulate and secrete:
- prostaglandins
- leukotrienes
- histamines
Why does atopic dermatitis predispose to allergic sensitisation?
Skin exposure more likely to lead to IgE response than oral exposure (oral promotes immune tolerance)
Which interleukin is most important in Th2 cell responses?
IL4
Why do filagrin mutations increase risk of allergic disease?
Increase risk of atopic dermatitis which increases allergen exposure
What represents a positive result in a skin-prick allergy test?
Wheal >3mm bigger than control
Recall 2 limitations of skin prick allergy testing
- risk of anaphylaxis (1 in 3000)
- poor positive predictive value
What can component resolved diagnostc testing be useful for?
For nuts, detection of storage protein is indicative of a stronger reaction
For wheat, detection of omega-5-gliadin is indicative of a stronger reaction
What is a measurement of mast cell tryptase used for?
Biomarker for anaphylaxis that peaks 1-2 hours following a reaction
Useful if diagnosis of anaphylaxis is not clear
What is the gold standard method of allergy testing/diagnosis?
Challenge tests
How should an allergy challenge test be performed?
Increase volume of allergen and measure response - it is the gold standard for food allergy diagnosis (done as a double blind)
Describe the symptoms of the oral allergy syndrome
Symptoms of allergy limited to mouth
Common allergens = birch pollen + rosacea fruit + ragweed + melons + mugwort + celery (due to cross reactivity)
Recall some foods that may trigger the Latex Food Syndrome?
Chestnut
Avocado
Banana
Potato
Tomato
Papaya
Kiwi
Aubergine
Mango
Wheat
Melon
Latex
What are the positive and negative controls used in skin prick testing?
Positive: histamine
Negative: diluent
Recall the management of anaphylaxis in adults
Elevate legs
100% oxygen
IM adrenaline 500 mcg
Inhaled bronchodilators
Hydrocortisone 200mg IV
Chlorphenamine 20mg IV
IV fluids
Seek help
allergic disorder is what type of hypersensitivity disorder
type 1
allergens trigger release of what Ig
IgE
what is the sensor in the TH2 immune memory response? what is released subsequently
mast cell = sensor
allergen causes cross linking of IgE
releasing histamine, prostaglandin and leukotriene
diagnosis of allergic disease requires what
history - occurs minutes to 3 hours after exposure, usually 2 organ systems involved
examination
allergic specific IgE (sensitisation) test
give 5 indications of an IgE RAST blood test
if patient can’t stop antihistamunes
patient has dermatogrophism
extensive eczema
history of anaphylaxis
borderline skin prick result
What cells and mediators in the IgE mechanism
masts cells and basophils
histamine and platelet activating factor
What cells and mediators in the IgG mechanism
macrophages and neutrophils
histamine and PAF
What cells and mediators in the complement mechanism
mast cells and macrophages
histamine and PAF
What cells and mediators in the pharmacological mechanism
mast cells
histamine and leukotriene
4 examples of IgE allergens
food, insect venom, ticks, penicillin
3 examples of IgG allergens
biologicals, blood and IgG transfusions
4 examples of complement allergens
lipid excipients, liposomes, dialysis membranes and polyethylene glycol
4 examples of pharmacological allergens
NSAIDS - aspirin
opiates
neuromuscular drugs
quinolone
give 2 conditions that mimic anaphylaxis but will not respond to IM adrenaline
C1 inhibitor deficiency - throat swelling
chronic urticaria and angiodema- ace inhibitors
how do you diagnose anaphylaxis
measurement of serum tryptase (specific marker for mast cell degranulation ) taken at 1, 3 and 24 hours post episode usually peaks around 3 hours and declines
persistent rise 24 hours after is suggestive of systemic mast cell disease suc as mastocytosis not anaphylaxis
treatment of anaphylaxis
IM dose of (0.5ml of adrenaline 1/1000).
what does the emergency community anaphylaxis kit containing
epic pen with 300 micrograms or half if child
prednisolone 20mg OD
cetirizine 10mg 0D (antihistamine)
outline the supportive treatment of anaphylaxis
100% oxygen
fluid replacement
IV hydrocortisone 100mg
IV chloramphenamine (for itch)
inhaled bronchodilators
alpha 1 mechanism in anaphylaxis
peripheral vasoconstriction
beta 1 mechanism in anaphylaxis
increases heart rate, contractility and BP
beta 2 mechanism anaphylaxis
relaxes bronchial smooth muscle and reduces release of inflammatory mediators
distinguish between food allergy and intolerance
allergy = immune response intolerance = non-immune
state a non IgE mediated disease
coeliac
state a cell mediated disease
contact dermatitis
what type of reaction is anaphylaxis
IgE mediated
what 3 tests are sensitisation tests be used first line
gold - skin prick (intardermal) - exclude allergy high NPV
RAST IgE blood test - exclude allergy high NPV
CRD - detects IgE to single protein components (e.g peanut and hazelnut)
what 3 tests are diagnostic
serum mast cell tyrptase - diagnose anaphylaxis
basophil activation - food and drug allergy
gold- allergen challenge - food and drug allergy
in what IgE mediated food allergy syndrome do cooked allergens cause no symptoms
OAS
IgE against alpga-gal (a1, 3-galactose) occur in what food allergy syndrome
delayed food induced anaphylaxis to beef, pork, lamb
exercise 4-6 hours after ingestion of allergen causes anaphylaxis in what syndrome
food associated exercise induced anaphylaxis
in skin prick what are the positive and negative controls
Histamine is injected as a positive control, saline as a negative.
Antihistamines must be stopped 48 hours prior to the test to allow for an accurate result.
whats latex food synfrome and oas
Latex food syndrome is an IgE mediated type 1 hypersensitivity reaction to fruits and seeds, that is caused by cross-reactivity to latex antigens. To have latex food syndrome, someone must also be allergic to latex. Common fruits that may cause symptoms include: Banana, pineapple or avocado. It is diagnosed via skin prick testing, demonstrating an allergy to latex and other foods.
Oral allergy syndrome refers to a collection of mild symptoms that occur when a patient eats typically stony fruit or some vegetables.
