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ANTIBODIES, protective proteins produced by cloned B lymphocyte-derived plasma cells. There are five classes of immunoglobulins, the most prevalent being immunoglobulin G (IgG), or gammaglobulin which provides the body's main defence against bacteria, viruses and toxins. Immunoglobulins are Y-shaped protein molecules consisting of two inner heavy POLYPEPTIDE chains, forming a Y, and, attached to the outer side of the short arms of the Y, two light polypeptide chains. The heavy chains are held together and the light chains held to the arms, by disulphide bonds. The short arms of the Y, with the light chains, are called the Fab (fragment antigen binding) section of the antibody. The antigen combining site lies between the open ends of the light and heavy chains. See also IgA, IgD, IgE, IgG and IgM. Some immunoglobulins are prepared as drugs for the management of RHESUS incompatibility and antibody deficiency; for the prophylaxis of MEASLES and hepatitis A; to minimize fetal damage when a pregnant woman is exposed to RUBELLA; and to assist in the treatment of TETANUS and RABIES. They are marketed under such brand names as Flebogamma, Gammabulin, Gammagard, Octagam, Rhophylac, Sandoglobulin, Vigam liquid and Winrho SDF.


Any of several types of globulin proteins that function as antibodies.

immunoglobulins (Ig) (antibodies) (im´ūnōglob´ūlinz),

serum pro-teins (g globulins) synthesized by plasma cells that act as antibodies and are important in the body's defense mechanisms against infection. See also antibody and allergen.
immunoglobulin, IgA,
n a type of immunoglobulin most commonly found in saliva, mucus, tears, urine, and other secretions.
immunoglobulin, IgD,
n a type of immunoglobulin that operates as antibodies. Trace amounts of IgD proteins are found in the blood serum and the plasma membranes of B lymphocytes.
immunoglobulin, IgE,
n a type of immunoglobulin that plays a role in regulating hypersensitivity reactions and reactions to parasitic infections.
immunoglobulin, IgG,
n a type of immunoglobulin that plays a role in secondary immune responses. It is unique in that it can pass through the placental barrier.
immunoglobulin, IgM,
n a type of immunoglobulin that reacts first to any given immune response.