Egg

Egg Yolk and Egg White as Food Allergens in the Human Body

Egg allergy is a common IgE-mediated food allergy, primarily affecting children, but some individuals continue to react into adulthood. Egg white is more allergenic than egg yolk, but both contain allergenic proteins that can trigger mild to severe allergic reactions, including anaphylaxis.

How Egg Allergy Develops in the Immune System

Initial Sensitization (Immune Priming)

• Egg proteins (allergens) are ingested → Some proteins, especially in egg white, are highly resistant to digestion.
• Dendritic cells in the gut-associated lymphoid tissue (GALT) present egg allergens to naive T-helper (Th2) cells.
• Th2 cells stimulate B-cells to produce IgE antibodies specific to egg proteins.
• IgE binds to mast cells and basophils, making them “sensitized” to egg allergens.

Subsequent Exposure (Allergic Reaction)

1. Egg proteins bind to IgE on mast cells, triggering mast cell degranulation.
2. Histamine, prostaglandins, and leukotrienes are released, leading to inflammatory symptoms:
   • Skin: Hives, eczema, swelling (angioedema)
   • Gastrointestinal tract: Nausea, vomiting, diarrhea, abdominal pain
   • Respiratory tract: Wheezing, coughing, shortness of breath
   • Systemic reaction: Anaphylaxis (severe cases)

Egg Yolk vs. Egg White: Allergenic Proteins and Their Role in Reactions

Egg White Allergens (More Allergenic)

Egg white contains four major allergenic proteins, with ovomucoid (Gal d 1) being the most potent.

Egg White Allergen	Protein Family	Molecular Weight	Immune Reaction	Heat Stability
Ovomucoid (Gal d 1)	Serine Protease Inhibitor	~28 kDa	Major allergen, responsible for persistent egg allergy	Highly stable (resists cooking & digestion)
Ovalbumin (Gal d 2)	Glycoprotein	~45 kDa	Most abundant egg white protein, triggers IgE responses	Moderately stable (denatures when cooked)
Conalbumin (Gal d 3)	Transferrin	~77 kDa	Iron-binding protein, moderate allergenicity	Heat-labile (degraded by cooking)
Lysozyme (Gal d 4)	Enzyme	~14 kDa	Used in food preservatives, possible cross-reactivity	Heat-labile (denatured by heat)

Egg Yolk Allergens (Less Allergenic)

Egg yolk proteins are less allergenic than egg white proteins but can still cause reactions in sensitive individuals.

Egg Yolk Allergen	Protein Family	Molecular Weight	Immune Reaction	Heat Stability
Alpha-Livetin (Gal d 5)	Serum Albumin	~66 kDa	Cross-reacts with bird serum albumin (Bird-Egg Syndrome)	Heat-labile (degraded by cooking)
Vitellogenin (Gal d 6)	Phosphoglycoprotein	~350 kDa	Moderate allergen, but rarely causes anaphylaxis	Moderately stable
Phosvitin	Phosphoprotein	~45 kDa	Minor allergen, rare reports of reactions	Heat-labile

Symptoms of Egg Allergy

Mild to Moderate Reactions

• Skin: Hives, swelling, eczema
• Gastrointestinal (GI): Nausea, vomiting, diarrhea, bloating
• Respiratory: Sneezing, coughing, nasal congestion
• Oral Allergy Syndrome (OAS): Itchy mouth/throat after consuming eggs

Severe Reactions (Anaphylaxis) Requires immediate administration of epinephrine (EpiPen®).

• Airway restriction: Difficulty breathing, throat swelling
• Drop in blood pressure (anaphylactic shock)
• Dizziness, fainting, confusion
• Swelling of lips, tongue, or face
• Tachycardia (rapid heartbeat)

Cross-Reactivity with Other Allergens

Egg proteins share structural similarities with poultry meat proteins, bird dander, and other animal-derived proteins, leading to cross-reactivity.

Cross-Reactive Allergen	Common Sources	Cross-Reactive Egg Protein
Chicken Meat	Poultry, processed meats	Gal d 5 (Livetin)
Bird Serum Albumin (Bird-Egg Syndrome)	Bird feathers, dander	Gal d 5 (Livetin)
Lysozyme	Food preservatives, cheese, pharmaceuticals	Gal d 4 (Lysozyme)

People with Bird-Egg Syndrome may react to both egg yolk and bird proteins due to alpha-livetin (Gal d 5) cross-reactivity.

Diagnosis of Egg Allergy

Skin Prick Test (SPT)

• Detects IgE-mediated allergic response to egg proteins.

Serum IgE Testing

• Measures specific IgE antibodies to egg allergens.

Oral Food Challenge

• Gold standard for confirming egg allergy, performed under medical supervision.

Component-Resolved Diagnostics (CRD)

• Detects specific egg allergens (Gal d 1, Gal d 2, etc.) to assess reaction severity and cross-reactivity risk.

Managing Egg Allergy

Strict Egg Avoidance

• Avoid all egg-based foods:
  • Whole eggs, egg whites, egg yolks
  • Processed foods with egg powder, albumin, lysozyme
  • Some baked goods, mayonnaise, sauces, vaccines (egg-based flu vaccine)

Alternative Egg-Free Options

Egg-Free Substitute	Safe Alternative
Baking (Egg Replacement)	Flaxseed meal, chia seed gel, apple sauce
Egg-Free Protein Sources	Lentils, tofu, soy protein
Vegan Egg Substitutes	Commercial egg replacers (e.g., JUST Egg)

Emergency Treatment

• Epinephrine injection (EpiPen®) for anaphylaxis.
• Antihistamines for mild allergic reactions.
• Corticosteroids for prolonged symptoms.

Conclusion

• Egg white is more allergenic than egg yolk, with ovomucoid (Gal d 1) as the most potent allergen.
• Egg yolk allergy (Gal d 5) can cross-react with bird proteins, causing Bird-Egg Syndrome.
• Egg allergens are partially heat-stable, meaning baked or processed eggs may still cause reactions.
• Cross-reactivity exists with poultry meat, bird dander, and lysozyme-containing foods.
• Severe egg allergy can lead to anaphylaxis, requiring strict avoidance and emergency preparedness (EpiPen®).