Immunopathogenesis of Food Allergy and Eosinophilic Gastrointestinal Disorders

Background: \- Food allergies are characterized by abnormal immune system responses to certain foods, such as peanuts, strawberries, and shellfish. Some individuals with these allergies have immediate allergic reactions on contact with the food in question and need immediate treatment to prevent severe complications. In contrast, eosinophil-associated gastrointestinal disorders are related disorders in which white blood cells in the intestinal tract react to certain foods, causing abdominal pain, nausea, and other digestion problems. Researchers are interested in studying these conditions to better understand how the immune system responds to food allergies. Objectives: * To examine how the immune system responds to food allergens. * To examine how certain white blood cells contribute to disease in individuals with food allergies and other inflammatory diseases. Eligibility: * Individuals between 18 and 65 years of age who have a history of (a) severe allergic reaction to peanuts (and have peanut-specific antibodies), (b) allergy or inflammatory disease, or (c) eosinophil-associated gastrointestinal disorder (with at least two documented food allergies). * Healthy volunteers between 18 and 65 years of age who have no known allergies or asthma. Design: * All participants will have a screening visit and a procedure visit. The procedure visit will take place within 30 to 60 days of the screening visit, and will take 3 to 4 hours depending on the procedure(s) done. * Participants will be screened with a physical examination and medical history, and will provide blood samples for testing. Participants with peanut or other allergies will have additional tests to determine their levels of sensitivity to certain foods. Participants with eosinophil-associated gastrointestinal disorder will provide stool samples for testing. * At the procedure visit, participants with peanut allergies and participants with other allergies will provide blood samples and have leukapherisis to collect white blood cells for examination. * At the procedure visit, healthy volunteers and participants with eosinophil-associated gastrointestinal disorder will provide blood samples and have leukapherisis to collect white blood cells for examination. In addition, some but not all of these participants will have a procedure called esophagogastroduodenoscopy (EGD), which will examine the esophagus, stomach, and small intestine. Participants who are scheduled to have EGD will be asked to fast for 6 hours before the procedure.