Omalizumab to Treat Eosinophilic Gastroenteritis

This study will evaluate the safety and usefulness of omalizumab (anti-IgE, Xolair) in reducing eosinophil counts and improving symptoms in patients with eosinophilic gastroenteritis (EG). EG is a disorder of unknown cause in which eosinophils, a type of white blood cell, are increased in the blood and gut tissue. Patients with EG have symptoms like stomach pain, bloating, and vomiting. About 50 percent of EG patients have food or environmental allergies, which may play a role in EG. Some patients with EG improve significantly on diets avoiding foods to which they are allergic. Immunoglobulin E (IgE) is an antibody that plays an important role in initiating allergic reactions. Omalizumab is a monoclonal antibody directed against IgE. The Food and Drug Administration approved omalizumab in 2003 for treating patients 12 years of age and older with allergic asthma. Patients between 12 and 76 years of age with eosinophilic gastroenteritis who have a blood eosinophil count of 500 or more and who have a food allergy or allergy to an inhaled allergen may be eligible for this study. Candidates are screened with a medical history, physical examination, and blood and urine tests. Participants undergo the following procedures: * Leukapheresis. This procedure is done to collect quantities of white blood cells to study the effects of omalizumab on eosinophils and other immune substances. Blood flows from a needle placed in an arm vein through a catheter (plastic tube) into a machine that separates the blood into its components by centrifugation (spinning). Some of the white cells are removed and the rest of the blood (red cells, plasma and platelets) is returned to the body through a needle in the other arm. * Skin testing. Participants are tested for allergies to specific substances. A small amount of various allergens (substances that cause allergies) are placed on the subject's arm. The skin is pricked at the sites of the allergens and the skin reaction after several minut