Mechanisms of Food Allergy

A food allergic reaction occurs as a result of some component of the immune system, which normally protects us from infectious agents, inappropriately reacting to the proteins in foods we eat.
Allergic reactions to foods can be broadly divided into immediate on-set and delayed on-set reactions.

IgE-Mediated Food Allergy

The parts of the immune system responsible for immediate on-set food allergic reactions (the most dramatic example of which is food anaphylaxis) are IgE antibodies.
In food allergic individuals (who are sometimes referred to as being “atopic”) eating certain food proteins (such as whey and casein protein contained in cow's milk) results in the production of specific IgE antibody molecules directed against the protein. The second time the individual eats the food, these specific IgE molecules interact with each other and with the protein, to cause the release of harmful chemicals (such as histamine) from special mast cells. This causes the damage associated with the symptoms of food allergy. Damage may occur to the skin, respiratory system or gastrointestinal tract, where the symptoms of food allergy are almost exclusively seen.


Non-IgE-Mediated Food Allergy

“T-cells” are the components of the immune system responsible for delayed-type food allergic reactions. In individuals with a predisposition for delayed on-set food allergy, initial ingestion of food protein leads to the production of specific types of “T-cell”. When the food is subsequently ingested, the food protein is “processed” in a variety of ways and “presented” to the previously generated food-specific T-cells. These T-cells then “invade” the area of the body about to suffer damage (e.g. skin, bowel). This processing, presenting and invasion can take 24-48 hours, which explains the delayed response. T-cells release chemicals that, through a chain of events, lead to the damage associated with symptoms of food allergy.