Food allergy is an abnormal immediate-type hypersensitivity immune inflammatory response to a food protein. Compelling evidence demonstrates that IgE antibodies mediate most of the key features of food allergy, including anaphylaxis.

Eight foods cause 90% of IgE-mediated food ige food allergy: cow’s milk, egg, wheat, soy, shellfish, fish, peanut and tree nut. These allergies result from a loss of key immune components that normally prevent benign food antigens from being recognized as pathogens.

Symptoms

IgE-mediated food allergies can manifest with a wide variety of symptoms. The most common symptoms include gastrointestinal symptoms like pain, nausea and diarrhea when a food allergen is ingested. The most severe reactions, including anaphylaxis, may involve multiple organ systems with cardiovascular and neurological involvement and are potentially fatal.

When a food triggers an allergic reaction in the immune system, dendritic cells and T helper 2 (Th2) cells release IgE molecules to capture and kill the offending food protein. This results in a symptom-producing antibody response by mast cells, leading to the release of mediators such as histamine.

A mild cutaneous reaction, such as erythematous rash, urticaria and/or localized edema, is often present in these patients. The gastrointestinal signs can range from a simple gastrointestinal upset to eosinophilic esophagitis (EoE). The cutaneous and gastrointestinal manifestations of these patients are characterized by rapid onset of symptoms upon ingestion of the offending food. They can be categorized as IgEmediated, non-IgE-mediated or mixed IgE and non-IgE-mediated conditions.

Diagnosis

The diagnosis of food allergy starts with a careful patient history. A detailed history can help guide the decision to pursue specific IgE testing versus other tests that are less reliable.

Specific IgE testing measures the level of IgE antibodies to the specific foods to which you are allergic. This test is conducted in a doctor's office. The result is typically available in one to two weeks and is reported as a number. High IgE levels to a particular food suggest that you are sensitized to the food and will likely experience symptoms upon ingestion.

IgE-mediated reactions involve the gastrointestinal, respiratory, or cardiovascular systems. Symptoms are due to the release of histamine, which causes the dilation of small blood vessels in these systems. Non-IgE mediated reactions involve other parts of the immune system and may be delayed in onset, typically hours after ingesting the offending food. These are the most common and tend to involve the gastrointestinal tract, with vomiting or diarrhea.

Treatment

Food allergies are associated with a variety of symptoms involving skin, respiratory and gastrointestinal tracts. Skin reactions, including urticaria and angioedema, are most common while GI-related symptoms include abdominal pain, diarrhea, and vomiting. These food allergy symptoms can be life threatening and require immediate treatment with epinephrine.

The development of food allergy is due to a loss of integrity in the key immune components that maintain tolerance to innocuous foods. This disruption leads to the recognition of benign food antigens as pathogens and induces inflammatory responses, which in turn promote class switching to IgE.

The resulting ige food allergy results in an abnormally high level of IgE antibodies against the relevant food allergens. Most children outgrow milk, egg and soy allergies during childhood and adolescence. However, peanut and tree nut allergy tend to persist and remain life-long. Allergen immunotherapy, a process of gradually increasing exposure to the suspected allergen over time, can be helpful in eliminating food allergies.

Prevention

Ige mediated allergy occur when there is a loss of integrity in key immune components that normally maintain a state of tolerance to benign food antigens and prevent them from being mistaken for pathogens. This type of allergy typically results in immediate-type hypersensitivity reactions to proteins in foods that are recognized by preformed allergen-specific IgE antibodies in the bloodstream and cause a rapid onset of symptoms (see Table 13).

Patients with IgE-mediated food allergy experience gastrointestinal symptoms, such as vomiting or diarrhea (food protein-induced enterocolitis syndrome or milk protein proctocolitis), abdominal pain, poor weight gain, and anemia, as well as rhinitis, asthma, and eczema of the skin. Occasionally, IgE-mediated food allergies can lead to a life threatening, whole-body allergic reaction called anaphylaxis.

Blood tests, which are less exact than skin tests but have a higher negative predictive value, can measure the presence of food-specific IgE antibody and help confirm a diagnosis. However, some people with IgE-mediated food allergy have a positive blood test but do not develop a clinically significant reaction following oral challenge, suggesting cross-reactivity to other foods.