Egg Allergens


Egg Proteins Overview

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Egg White Allergens

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Ovomucoid (Gal d 1)
  • Dominant allergen in egg white, possibly due to its stability
  • In children, persistent egg allergy was associated with higher sIgE levels to ovomucoid than children who outgrew their egg allergy. Resolution was associated with the absence or decline in ovomucoid sIgE level.
  • Gastric digestion can reduce the allergenicity of ovomucoid, which can explain why some patients have skin contact reactions to egg, but not ingestion reactions
  • Heating may decrease allergenicity by blocking epitope access through interactions with the food matrix
    and causing conformational change that may decrease allergenicity
  • Ovomucoid may predict outcome of baked egg challenges
    • In one study with challenges to heated and unheated egg white powder, sIgE to ovomucoid >11 kU/L correlated with a high risk (95% specific) of reacting to heated (as well as raw) egg white, whereas a level <1 kU/L correlated with a low risk of reaction (95% sensitive) to heated egg white, even if the patient might react to raw egg white
    • In a study with challenges to heated egg in muffin and waffle, ovomucoid sIgE level of 50 kU/L was more than 90% predictive, whereas an undetectable level of ovomucoid-specific IgE still carried a 10% chance of heated egg reactivity
  • A lower ovomucoid sIgE/IgG4 ratio is associated with heated egg tolerance
Ovalbumin (Gal d 2)
  • Most abundant (54%) protein in egg white
  • Heating may decrease allergenicity by blocking epitope access through interactions with the food matrix
    and causing conformational change that may decrease allergenicity
  • A lower ovalbumin sIgE/IgG4 ratio is associated with heated egg tolerance
Ovotransferrin, also known as conalbumin (Gal d 3)
  • Role of sIgE antibody to ovotransferrin in the diagnosis of egg allergy has not been determined
Lysozyme (Gal d 4)
  • Commonly used as a food preservative and in some pharmaceuticals and foods (e.g. eye drops and cheese) therefore individuals sensitized to lysozyme may react when exposed to such products
  • Considered an important occupational allergen, causing asthma via the inhalation route
Other
  • Egg white cystatin
  • Lipocalin-type prostaglandin D synthase (L-PGDS)
  • Recently identified allergen candidates, unclear clinical significance


Egg Yolk Allergens

  • Not a significant cause of egg allergy
Chicken serum albumin, also known as alpha-livetin (Gal d 5)
  • Bird-egg syndrome
    • Primary sensitization to chicken serum albumin (feathers, serum, droppings, and meat) resulting in food allergy to serum albumin in egg yolk
      • Only a minority of patients with bird feather allergy report chicken meat allergy likely because the allergen is altered by cooking
    • Most frequently observed in individuals with frequent exposure to birds (bird fanciers, etc.)
Other
  • Vitellenin (apovitellenin I)
  • Apoprotein B (apovitellenin VI)
  • Other egg yolk allergens with unclear clinical significance


Egg Allergen Cross-reactivity



Egg Allergy Phenotypes

  • Patients with IgE against sequential epitopes tend to have persistent allergy, whereas those with IgE against conformational epitopes tended to have transient allergy
  • Majority (74%) of children with egg allergy tolerate extensively heated egg (e.g. muffin and waffle made with eggs), and tolerance is gained twice as rapidly to well-cooked egg than uncooked egg (median age resolution 5.6 years vs. 10.3)
  • Low ovomucoid sIgE may predict tolerance of heated egg
  • Low ovomucoid and ovalbumin sIgE/IgG4 ratios are associated with heated egg tolerance
  • Higher egg white sIgE level is associated with persistent baked and regular egg reactivity, while initial baked egg reactivity is not


Diagnosis

  • Skin prick test

  • Specific IgE

    • Tests available from Phadia
      • Complete allergen
        • Egg white
        • Egg yolk
      • Component resolved diagnostics
        • Ovomucoid (nGal d 1)
        • Ovalbumin (nGal d 2)
        • Ovotransferrin/conalbumin (nGal d 3)

    • Performance of egg white sIgE in predicting baked egg OFC in a retrospective study of 100 children (anaphylaxis to egg within 2 years or convincing reaction to baked egg within 6 months excluded). No difference in egg white skin test size (median 7 mm) between OFC pass/fail groups.
      baked egg sige performance.png


  • Specific IgG4

    • Ovalbumin and ovomucoid specific IgG4 may be useful when interpreted as IgE/IgG4 ratios (see above)

  • Statistical model using IgE and IgG4 levels

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    • A statistical model including ovalbumin and ovomucoid IgE and IgG4 levels was superior to IgE alone in predicting outcome of heated egg challenge
    • Equation: 1/(1+exp(-2.33 + 0.26(sIgE OVA) + 0.19(sIgE to OVM) - 0.18(sIgG4 to OVA) + 0.99(sIgG4 to OVM) - 0.12(sIgE to OVA x sIgG4 to OVA) - 0.34(sIgE to OVM x sIgG4 to OVM)))
      • If egg white sIgE <7 and if statistical model
        • >0.18, 47% with positive baked egg challenge
        • <0.18, 7-8% with positive baked egg challenge
      • If egg white sIgE >7 and if statistical model
        • >0.18, 85% with positive baked egg challenge
        • <0.18, 100% with positive baked egg challenge
  • Oral food challenge



Egg Allergy Monitoring



Egg Allergy Natural Course



Egg Ladder

  • Resolution of egg allergy tends to occurs in stages starting with tolerance to well-cooked egg (e.g. cake), then lightly cooked egg (e.g. scrambled) followed finally by raw egg

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Egg OFC Protocols


HealthNuts

  • Designed for 1 year old infant
  • Challenge material: egg white from 60 g free-range hen's egg. After the initial dose, the allergen is mixed with an age-appropriate previously tolerated food (eg, apple sauce or yogurt) on the basis of preferred parental choice of food.
  • Interval: 15 min
    • Drop inside lip (not to touch outside lip)
    • 0.5 mL
    • 1 mL
    • 2 mL
    • 5 mL
    • 10 mL
    • Remainder of the 60 g egg white (usually 10-13 mL)

Oral food challenges and baked egg challenge protocols




Vaccines Containing Egg







References