IgE-mediated food allergies are true food allergies involving an abnormal response of the immune system to one or more specific foods. These reactions are associated with the rapid onset of symptoms – usually within a few minutes to a few hours after the ingestion of the offending food.
Immediate hypersensitivity reactions are mediated by an allergen-specific immunoglobulin E (IgE) antibody. The food allergens involved in IgE-mediate reactions are typically naturally-occurring proteins in foods.
In IgE-mediated food allergies, exposure to the allergen stimulates the production of allergen-specific IgE antibodies by plasma cells in susceptible individuals. The allergen-specific IgE attaches itself to the surface of mast cells in various tissues and basophils in the blood in a process known as sensitization. No symptoms occur during the sensitization phase but, once that phase is completed, the individual is primed to react to the offending allergen.
Upon subsequent exposure to the allergenic food, the allergen cross-links IgE molecules on the surface of the mast cell or basophil membrane causing these cells to release various mediators of the allergic reaction into the bloodstream and tissues.
Histamine is one of the most important mediators of the immediate hypersensitivity reaction. Histamine alone can elicit inflammation, pruritis (itching), and contraction of the smooth muscles in the blood vessels, gastrointestinal tract, and respiratory tract. Several dozen physiologically active mediators of the allergic reaction have been identified.
Other important mediators include various leukotrienes and prostaglandins. The released mediators interact with receptors in various tissues eliciting a wide range of physiologic responses. Because the mediators are released into the bloodstream, systemic reactions involving multiple tissues and organs can ensue.
Other allergies also occur through this same IgE-mediated mechanism including allergies to pollens, mold spores, animal danders, dust mites, certain drugs (e.g. penicillin), and bee venom. Susceptible individuals may form allergen-specific IgE to one or several substances in their environment including food allergens.
A number of different symptoms can be associated with IgE-mediated food allergies. The symptoms of IgE-mediated reactions can involve the gastrointestinal tract, skin, or respiratory tract. Some symptoms of food allergy are potentially quite severe, with anaphylactic shock being the most severe.
IgE-mediated food allergies affect an estimated 6 - 8% of infants and children and 2 – 3% of adults in the United States.
The major approach to the treatment for true food allergies is their prevention their occurrence through implementation of a specific avoidance diet.
Peanuts, soybeans, fish, crustacea, milk, eggs, tree nuts, and wheat are considered the most common allergenic foods on a worldwide basis. These eight food groups account for approximately 90% of all IgE-mediated food allergies (sometimes referred to as the “Big Eight”).
Many facts about food allergies are misunderstood. Here is a list of common misconceptions about food allergies along with the corresponding facts.