Immuno - allergy

Question 1

How does the immune system recognise + respond to allergens?

Answer 1

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

Question 2

How do Th2 cells signal to activate eosinophils and basophils

Answer 2

IL-4, IL-5, IL-13

Question 3

Oral vs skin exposure to allergens - what’s the difference?

Answer 3

Oral - IgG + IgA response

Skin - IgE production due to skin DCs being efficient in priming Th2 responses

Question 4

clinical fx of an allergic response? Refer to 5 different systems

Answer 4

Skin - flush/angioedema/urticaria
Resp - SOB/cough/wheeze/rhinorrhoea
GI - N/V/D
Vascular/CNS - syncope/sense of doom

Question 5

relevant Ix for allergic disease?

Answer 5

At time of reaction = SERUM TRYPTASE

• Skin prick
• lab measurement of IgE
• Component resolved diagnostics
• Challenge test

Question 6

+ve result for skin prick testing?

Answer 6

wheal >3mm

Question 7

Describe a skin prick test

Answer 7

Measure local wheal + flare response compared to +ve AND -ve control
+ve control = histamine
-ve control = diluent

Question 8

Disadvantages of a skin prick test

Answer 8

• High false +ve rate
• Must stop antihistamines 48 hours prior to test
• Useless in extensive eczema
• Risk of anaphylaxis

Question 9

Describe a serum specific IgE blood test

Answer 9

Serum is added to a cup containing allergen + fluorescently labelled anti-IgE antibody

• Fluorescent signal is measured

Question 10

3 indications for serum specific IgE blood test?

Answer 10

• Pt with anaphylaxis Hx
• Pt with extensive eczema
• Pt who can’t stop antihistamines

Question 11

Describe component resolved diagnostics (CRD)?

Answer 11

Blood test to see if IgE binds to single protein components

Heat and proteolysis stable proteins = assoc with severe allergy

Question 12

Gold standard Ix for food and drug allergy?

Answer 12

Challenge test - supervised ingestion of offending food/drug

Question 13

Which Ix should be done at time of allergic episode?

When is it at its peak? when should it be done?

Answer 13

• Mast cell tryptase (released in mast cell degranulation)
• Peak at 1-2 hours
• Measure at 1, 3 and 24 hours

Question 14

Criteria for diagnosis of anaphylaxis if allergen exposure is unknown?

Answer 14

Skin involvement + at least 1 of:

• Resp Sx
• Hypotension Sx

Question 15

Criteria for diagnosis of anaphylaxis if there is likely allergen exposure?

Answer 15

2 or more of:

• Resp Sx
• Hypotension Sx
• Skin Sx
• GI Sx

Question 16

Criteria for diagnosis of anaphylaxis if there is known allergen exposure?

Answer 16

Hypotension Sx alone

Question 17

4 types of anaphylaxis - IgE, IgG, complement and pharmacological.

What allergens tend to cause each of these?

Answer 17

IgE - food/venom/penicillin
IgG - biologics/transfusions
Complement - PEG/dialysis membranes
Pharm - NSAIDs/opioids

Question 18

Ddx for anaphylaxis

Answer 18

Skin - ACEis can cause urticaria
CV - MI, PE
Panic attack
Severe asthma
Pheochromocytoma

Question 19

Dose and administration of adrenaline in acute anaphylaxis?

Answer 19

IM adrenaline 500mcg

Question 20

Immediate management of anaphylaxis

Answer 20

IM adrenaline 500mcg
Elevate legs
100% O2
IV fluids
Inhaled bronchodilators
IV hydrocortisone 100mg
IV chlorpheniramine 10mg

Question 21

Which drug +dose is given to prevent late phase response in acute anaphylaxis

Answer 21

IV hydrocortisone 100mg

Question 22

Which drug + dose is given to treat skin rash in anaphylaxis

Answer 22

IV chlorpheniramine 10mg

Question 23

5 things which must be done once acute Mx of anaphylaxis is done

Answer 23

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

Question 24

What is in an epipen?

Answer 24

300mcg adrenaline + 20mg prednisolone

Question 25

Food allergy vs intolerance?

Answer 25

Allergy - specific immune response, repeatable on exposure to specific food

Intolerance - non-immune response e.g. food poisoning, lactose intolerance

Question 26

Major RF for food allergy??

Answer 26

Atopic dermatitis

Question 27

2 main Ix for ?food allergy

Answer 27

Serum specific IgE test or challenge test(gold standard)

Question 28

Eg of non-IgE mediated symptoms in response to food?

Answer 28

Fatigue, migraine, hyperactivity

Question 29

Name 4 IgE-mediated food allergy syndromes

Answer 29

• Anaphylaxis
• Oral allergy syndrome
• Food-associated, exercise-induced anaphylaxis
• Delayed, food-induced anaphylaxis

Question 30

Typical food allergens in anaphylaxis

Answer 30

Peanut
Shellfish
Milk
Eggs

Question 31

Describe food-associated, exercise-induced anaphylaxis, and the typical foods which cause it?

Answer 31

Ingestion of certain foods causes anaphylaxis if pt exercises within 4-6 hours of ingestion

Wheat, shellfish, celery

Question 32

Food allergy syndrome which is particularly associated with meat? What is the pathophysiology?

Answer 32

Delayed, food-induced anaphylaxis

IgE against alpha1,3-galactose

Question 33

What particular event can induce delayed, food-induced anaphylaxis

Answer 33

Tick bites

Question 34

Describe oral allergy syndrome’s pathophysiology

Answer 34

Limited to the oral cavity

Respiratory exposure to pollen –> cross reactivity with food (stone fruits, carrots, nuts)