Immuno - allergy Flashcards
How does the immune system recognise + respond to allergens?
Allergens cause tissue damage (epithelial barrier breakdown + increased protease activity) –> Epi cells signal to Th2 cells
- Th2 cell activation
- Th2 cells release IL 4+5+13
- Basophil + eosinophil activated
- Histamine + leukotrine release
How do Th2 cells signal to activate eosinophils and basophils
IL-4, IL-5, IL-13
Oral vs skin exposure to allergens - what’s the difference?
Oral - IgG + IgA response
Skin - IgE production due to skin DCs being efficient in priming Th2 responses
clinical fx of an allergic response? Refer to 5 different systems
Skin - flush/angioedema/urticaria
Resp - SOB/cough/wheeze/rhinorrhoea
GI - N/V/D
Vascular/CNS - syncope/sense of doom
relevant Ix for allergic disease?
At time of reaction = SERUM TRYPTASE
- Skin prick
- lab measurement of IgE
- Component resolved diagnostics
- Challenge test
+ve result for skin prick testing?
wheal >3mm
Describe a skin prick test
Measure local wheal + flare response compared to +ve AND -ve control
+ve control = histamine
-ve control = diluent
Disadvantages of a skin prick test
- High false +ve rate
- Must stop antihistamines 48 hours prior to test
- Useless in extensive eczema
- Risk of anaphylaxis
Describe a serum specific IgE blood test
Serum is added to a cup containing allergen + fluorescently labelled anti-IgE antibody
- Fluorescent signal is measured
3 indications for serum specific IgE blood test?
- Pt with anaphylaxis Hx
- Pt with extensive eczema
- Pt who can’t stop antihistamines
Describe component resolved diagnostics (CRD)?
Blood test to see if IgE binds to single protein components
Heat and proteolysis stable proteins = assoc with severe allergy
Gold standard Ix for food and drug allergy?
Challenge test - supervised ingestion of offending food/drug
Which Ix should be done at time of allergic episode?
When is it at its peak? when should it be done?
- Mast cell tryptase (released in mast cell degranulation)
- Peak at 1-2 hours
- Measure at 1, 3 and 24 hours
Criteria for diagnosis of anaphylaxis if allergen exposure is unknown?
Skin involvement + at least 1 of:
- Resp Sx
- Hypotension Sx
Criteria for diagnosis of anaphylaxis if there is likely allergen exposure?
2 or more of:
- Resp Sx
- Hypotension Sx
- Skin Sx
- GI Sx
Criteria for diagnosis of anaphylaxis if there is known allergen exposure?
Hypotension Sx alone
4 types of anaphylaxis - IgE, IgG, complement and pharmacological.
What allergens tend to cause each of these?
IgE - food/venom/penicillin
IgG - biologics/transfusions
Complement - PEG/dialysis membranes
Pharm - NSAIDs/opioids
Ddx for anaphylaxis
Skin - ACEis can cause urticaria CV - MI, PE Panic attack Severe asthma Pheochromocytoma
Dose and administration of adrenaline in acute anaphylaxis?
IM adrenaline 500mcg
Immediate management of anaphylaxis
IM adrenaline 500mcg Elevate legs 100% O2 IV fluids Inhaled bronchodilators IV hydrocortisone 100mg IV chlorpheniramine 10mg
Which drug +dose is given to prevent late phase response in acute anaphylaxis
IV hydrocortisone 100mg
Which drug + dose is given to treat skin rash in anaphylaxis
IV chlorpheniramine 10mg
5 things which must be done once acute Mx of anaphylaxis is done
1) investigate the cause
2) refer to allergy + dietitian
3) provide written info (Sx, triggers, how to use epipen)
4) Provide emergency kit
5) Copy Mx plan to GP, school, carers etc
What is in an epipen?
300mcg adrenaline + 20mg prednisolone
Food allergy vs intolerance?
Allergy - specific immune response, repeatable on exposure to specific food
Intolerance - non-immune response e.g. food poisoning, lactose intolerance
Major RF for food allergy??
Atopic dermatitis
2 main Ix for ?food allergy
Serum specific IgE test or challenge test(gold standard)
Eg of non-IgE mediated symptoms in response to food?
Fatigue, migraine, hyperactivity
Name 4 IgE-mediated food allergy syndromes
- Anaphylaxis
- Oral allergy syndrome
- Food-associated, exercise-induced anaphylaxis
- Delayed, food-induced anaphylaxis
Typical food allergens in anaphylaxis
Peanut
Shellfish
Milk
Eggs
Describe food-associated, exercise-induced anaphylaxis, and the typical foods which cause it?
Ingestion of certain foods causes anaphylaxis if pt exercises within 4-6 hours of ingestion
Wheat, shellfish, celery
Food allergy syndrome which is particularly associated with meat? What is the pathophysiology?
Delayed, food-induced anaphylaxis
IgE against alpha1,3-galactose
What particular event can induce delayed, food-induced anaphylaxis
Tick bites
Describe oral allergy syndrome’s pathophysiology
Limited to the oral cavity
Respiratory exposure to pollen –> cross reactivity with food (stone fruits, carrots, nuts)
