July 21, 2006 Researchers have identified one of the proteins that may be responsible for causing food allergies, which could lead to the development of more accurate non-invasive tests to identify true food allergies, according to a study published in the July issue of Gastroenterology, the journal for the members of the American Gastroenterological Association.
Food allergies often present a unique problem for allergy testing since not every patient has detectable levels of immunoglobulin E (IgE) in their serum, especially patients with delayed allergies. A number of reliable testing methods exist for food and other allergies, including skin tests and serum IgE tests, however, they may not accurately diagnose food allergies. The oral food challenge is considered the most accurate test for food allergies but is expensive to administer and has to be done in a controlled environment. Immunoglobulin (antibody) E is a protein produced by plasma cells (or B-Cells , a type of lymphocyte ), which is designed to control the immune response in extracellular fluids by binding to substances in the body that are recognized as foreign.
The study, conducted at the Mount Sinai School of Medicine, New York, showed for the first time that CD23, a protein normally expressed in a person's intestinal tract, acts as a receptor for IgE, a protein associated with allergic reactions, and enables it to participate in food-allergic reactions.
"We believe that the presence of CD23 may provide a surrogate method of looking at the gut without invasive tests like biopsies," according to M. Cecilia Berin, PhD, assistant professor, pediatrics/allergy and immunology, Mount Sinai and lead author of the study.
Results of this study showed that CD23 was detectable in stool samples from food allergic patients, but not the controls, suggesting either increased levels of CD23 on intestinal cells or an allergen-induced shedding of CD23 in food allergic patients. Additionally, researchers found a strong correlation between the level of CD23 and food-specific IgE in the stool, demonstrated by the availability of IgE antibodies to interact with CD23 on the outside surface of the gastrointestinal wall.
Researchers collected stool samples from nine pediatric patients (age range three to 17 years) who underwent an oral food challenge, during which they were administered either egg or milk in a controlled environment. All patients had a history of allergies to these foods and had reacted positively through other testing methods. Their symptoms, which occurred less than two hours after the food challenge, included skin reactions, breathing problems and gastrointestinal problems or a combination. They were matched to five pediatric controls with no food allergies.
"Based on the results of our study, we intend to conduct larger scale trials of patients with food allergic disorder to determine how CD23 in the stool correlates with clinical findings," according to Dr. Berin. "We hope to determine that CD23 offers a promising target for food allergies that leads to more accurate, easier to tolerate tests for these patients."
Food allergies affect an estimated six to eight percent of American children age four years or younger and approximately two percent of adults, according to the National Institute of Allergy and Infectious Diseases (NIAID). The study authors estimate that three and a half to four percent of these food allergies are IgE-mediated. While many people believe they have food allergies, the majority of individuals experience food intolerance.
Food allergies are an exaggerated immune response in which the body produces histamines and antibodies that induce symptoms in the gastrointestinal tract, airways and skin, and in the most severe cases induces anaphylactic shock, an often fatal systemic reaction. These allergies are often characterized by abdominal pain, diarrhea, vomiting, hives, swelling of the eyelids, face, lips and tongue, shortness of breath or wheezing and difficulty swallowing, among other symptoms. The most common allergens are peanuts, tree nuts, shellfish, fish, wheat, milk, eggs and soy.
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