Immuno: Allergy Pt.2

Question 1

When does mast cell tryptase reach peak levels and return to baseline levels?

Answer 1

• Peak = 1-2 hours
• Baseline = 6-12 hours

NOTE: if it fails to return to baseline, it may suggest systemic mastocytosis

Question 2

When might mast cell trypase be measured?

Answer 2

If the diagnosis of anaphylaxis is unclear (e.g. hypotension and rash during anaesthesia)

NOTE: it has lower sensitivity for food-induced anaphylaxis

Question 3

Describe how the basophil activation test works

Answer 3

• Measures basophil response to allergen IgE crosslinking
• When activated, basophils increases CD64, CD203, CD300
• This upregulation is detected using flow cytometry

Question 4

What is the gold standard test for diagnosing food and drug allergy?

Answer 4

Challenge test

Question 5

Describe how challenge tests are carried out.

Answer 5

• Increasing volumes of the offending food/drug are ingested
• Observe a reaction
• Done under close medical supervision
• Risk of severe reaction

Question 6

Define anaphylaxis.

Answer 6

A severe, potentially life-threatening systemic hypersensitivity reaction characterised by rapid-onset airway, breathing and circulatory problems which are often associated with skin and mucosal changes.

NOTE: skin is the most frequent organ involved

Question 7

List some clinical features of anaphylaxis

Answer 7

Skin (most commonly involved organ) - urticaria, itch, angioedema

CVS - hypotension, tachycardia, syncope

Respiratory - SoB, wheeze, stridor, hypoxia

Respiratory symptoms more common in children, CVS symptoms more common in adults

Question 8

List some mechanisms of anaphylaxis.

Answer 8

• IgE - mast cells and basophils - histamine and PAF (triggered by food, venom, ticks, penicillin)
• IgG - macrophages and neutrophils - histamine and PAG (triggered by blood product transfusions)
• Complement - mast cells and macrophages - histamine and PAF (triggered by lipid excipients, liposomes, dialysis membranes)
• Pharmacological - mast cells - histamine and leukotrienes (triggered by NSAIDs)

Question 9

List some reactions that can mimic anaphylaxis.

Answer 9

• Skin - chronic urticaria and angioedmea (ACE inhibitors)
• Throat swelling - C1 inhibitor deficiency
• CVS - MI and PE
• Respiratory - severe asthma, inhaled foreign body
• Neuropsychiatric - anxiety/panic disorder
• Endocrine - carcinoid, phaeochromocytoma
• Toxic - scromboid toxicity (histamine poisoning)
• Immune - systemic mastocytosis

Question 10

Describe the emergency management of anaphylaxis. What dose and concentration of adrenaline is used?

Answer 10

0.5mL of 1:1000 (>12 years old)

Question 11

Describe the refractory anaphylaxis protocol and when is it used?

Answer 11

No respiratory or CVS symptom improvement after 2 IM adrenaline doses

Question 12

Describe the mechanism of action of adrenaline in treating anaphylaxis.

Answer 12

• Alpha 1 - peripheral vasoconstriction, reverses low BP and mucosal oedema
• Beta 1 - increases HR, contractility and BP
• Beta 2 - relaxes bronchial smooth muscle, reduces release of inflammatory mediators

Question 13

List some measures that may be taken in the ongoing management of a patient who has experienced an episode of anaphylaxis.

Answer 13

• Referral to allergy clinic
• Investigate cause
• Written information on recognition of symptoms, trigger avoidance and indications for self-treatment with EpiPen
• Prescription of emergency kit to manage anaphylaxis
• Copy of management plan for patients, parents and school staff and GP
• Immunotherapy/drug desensitisation (if indicated)
• Refer to dietician (if food-induced)
• Advise getting MedicAlert bracelet
• Utilise patient support groups (Anaphylaxis Campaign)

Question 14

Which commonly used drug can cause angioedema?

Answer 14

ACE inhibitors

NOTE: this can happen at any point when taking ACE inhibitors (i.e. even several years after being on ACE inhibitors)

Question 15

What is the key difference between food allergy and food intolerance?

Answer 15

The mechanism behind food intolerance is NOT immunological

Question 16

List some types of food intolerance.

Answer 16

• Food poisoning
• Enzyme deficiency (e.g. lactose intolerance)

Question 17

List some types of food allergy.

Answer 17

• IgE mediated - anaphylaxis
• Mixed IgE and cell-mediated - atopic dermatitis
• Non-IgE mediated - coeliac disease
• Cell-mediated - contact dermatitis

Question 18

Which investigations are usually used to confirm the diagnosis in patients with a clinical history suggestive of food allergy?

Answer 18

Skin prick test or specific IgE blood test

Gold standard is oral food challenge

Question 19

List some IgE-mediated food allergy syndromes.

Answer 19

• Anaphylaxis (e.g. peanut)
• Food-associated exercise-induced anaphylaxis (ingestion of food leads to anaphylaxis if the individual exercises within 4-6 hours of ingestion (e.g. wheat, shellfish))
• Delayed food-induced anaphylaxis to beef/pork/lamb (symptoms occur 3-6 hours after ingestion, induced by tick bites)
• Oral allergy syndrome (limited to oral cavity with swelling and itching, occurs after pollen allergy is established, caused by cross-reaction of IgE antibody to pollen with stone fruits (e.g. apples), vegetables and nuts)

Question 20

Which cytokine is key for development of eosinophils

Answer 20

IL-5