Immunoglobulin E (IgE) is a protein called an antibody that is produced by cells in the body known as lymphocytes. IgE is primarily involved in the allergic response. Some patients can react to various allergens, such as pollen, medications, or food. When a patient encounters an allergen, IgE binds to cells known as mast cells. These mast cells are activated to release granules of histamine, which then produces symptoms of an allergic response.
Lymphocytes that originate and mature in the bone marrow are known as B-lymphocytes. These B-cells secrete different types of antibodies or immunoglobulins and are part of the humoral immune response. When a patient is first exposed to an allergen, some of these B-cells are activated and begin to secrete immunoglobulin E. This IgE binds to the surface of mast cells present in tissues of the body. It can also bind to other cells in the blood called basophils.
After the first exposure to allergen, the mast cells and basophils are sensitized, but no allergic reaction has taken place. At the time of the second exposure, the allergen binds to the immunoglobulin E molecules on the cell surface. The IgE molecules then become linked to each other by the allergen, which signals the cells to release granules containing histamine, enzymes, or other proteins known as cytokines.
This IgE response is very potent and can begin within two to 30 minutes of exposure to the allergen. Release of histamine or other proteins can irritate mucus membranes, cause blood vessels to dilate, or cause smooth muscles of the airways to constrict. Symptoms for the patient can range from sneezing and hay fever to the life-threatening signs of anaphylactic shock.
Identification of the substance producing the immunoglobulin E response is the first step in treatment. The patient may already know what triggers the response. If not, the physician may want to use a skin test for diagnosis. Extracts of pollen, dust, foods, or medications are placed on the skin, followed by a small needle stick. If the patient is allergic to any of the substances, a small inflamed area will develop at that site on the skin.
Treatment for allergies starts with having the patient avoid the cause of the response. Most food allergens or medications can be avoided. For patients with mild symptoms of hay fever, an anti-histamine medication may relieve symptoms. Anti-histamines do not prevent the immunoglobulin E response, but rather block the action of the histamine once it is released from granules.
If an allergen is airborne or contact cannot be controlled, as in a bee sting, the patient may need to have immunotherapy. Injections of very small doses of the allergen are given under the skin to sensitize the patient and control the response. These injections are usually given twice a week for a few months.