Allergy Flashcards

1
Q

Th2 Response

A

o Stressed or damaged epithelium will release signalling cytokines

o Cytokines act on Th2, Th9 and ILC2 (Innate Lymphoid Cells T2) - promote the section of IL4, IL5 and IL13

 IL-4 stimulates B-cells to produce IgE and IgG4

o These then act on eosinophils and basophils which contribute to tissue injury

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2
Q

Oral vs skin exposure

A

 When an allergen is ingested through the oral route, T-regs (from GI mucosa) inhibit IgE synthesis
 Oral tolerance requires induction of CD4+ T-reg cells
 T-regs inhibit multiple pro-allergic functions such as inhibiting DC APC function, secretion of IL-10, etc.

Whereas skin and respiratory exposure induces IgE sensitisation

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3
Q

Th2 immune memory responses

A

o The sensor is the mast cell - allergen causes cross-linking of IgE - histamine, prostaglandins and leukotrienes
o These act on the endothelium  increased permeability, smooth muscle contraction and neuronal itch

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4
Q

IgE RAST (radioallergosorbent) blood tests

A

o (1) Allergen bound to sponge in a plastic cap and patient’s serum is added
o (2) Specific IgE (if present) binds to allergen
o (3) Anti-IgE antibody tagged with a fluorescent label is added
o (4) Amount of IgE/Anti-IgE is measured by fluorescent light signal

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5
Q

Functional allergen tests

A

• Serial mast cell tryptase
o Tryptase is a pre-formed protein found in mast cell granules
o Peak concentration = 1-2 hours
o Useful if diagnosis of anaphylaxis uncertain (e.g. hypotension/rash in anaesthesia)

• Basophil activation test:
o Measurement of basophil response to allergen IgE cross-linking
o Activated basophils increase expression of CD63, CD203 and CD300 protein

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6
Q

In vivo test: open or blinded allergen challenge

A
  • GOLD STANDARD for food and drug allergy diagnosis
  • Increasing volumes of the offending food/drug are ingested
  • Take place under close medical supervision
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7
Q

Allergen-specific IgE sensitisation test

A

o Skin prick and blood tests are used to detect the presence/absence of IgE antibody against external proteins
 IMPORTANT: a positive IgE test only demonstrates sensitisation, NOT clinical allergy

80% who have peanut AB are asymptomatic

 Concentration – higher levels = more symptoms
 Affinity to target – higher affinity = increased risk

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8
Q

Indications of Ice RAST test

A

o Patients who can’t stop antihistamines (otherwise do skin test)
o Patients with dermatographism
o Patients with extensive eczema
o History of anaphylaxis
o Borderline/equivocal skin prick test results

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9
Q

Diagnosis of anaphylaxis

A

o Serial measurement of serum tryptase (a highly specific marker for mast cell degranulation)
o Samples taken 1 hour, 3 hours and 24 hours post episode of anaphylaxis
o The rise in tryptase concentration is directly proportional to fall in BP
o DIAGNOSIS = persistent rise in tryptase 24 hours after allergic reaction suggestive of systemic mast cell disease

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10
Q

Management of anaphylaxis

A

 IM ADRENALINE (1 in 1,000)

 Adjust body position 100% Oxygen
 Fluid replacement Inhaled bronchodilators
 Hydrocortisone 100 mg IV (prevent late phase response) Chlorpheniramine 10 mg IV (skin rash)

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11
Q

Reactions that mimic anaphylaxis

A

o SKIN: Chronic urticaria and angioedema (ACE inhibitors)
o THROAT SWELLING: C1 inhibitor deficiency
o CARDIOVASCULAR: Myocardial infarction and PE
o RESPIRATORY: Very severe asthma, vocal cord dysfunction, inhaled FB
§

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12
Q

Investigation for food allergy

A

o Double-blind oral food challenge = gold standard

o Skin-prick test or specific IgE blood test (useful to confirm a clinical history; useful to exclude allergy)

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13
Q

What each allergy test is useful for

A

Serial mast cell tryptase- anaphylaxis
Basophil activation- Diagnosis of food and drug allergy
Allergen challenge- Diagnosis of food and drug allergy- gold standard

Skin prick (intradermal)- To exclude allergy (high NPV)

RAST IgE blood test- To exclude allergy (high NPV)
When skin prick is not possible (i.e. cannot take antihistamine)

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