The American Heritage® Dictionary of the English Language, 4th Edition
n. Any of a group of large glycoproteins that are secreted by plasma cells and that function as antibodies in the immune response by binding with specific antigens. There are five classes of immunoglobulins: IgA, IgD, IgE, IgG, and IgM.
n. Any of the glycoproteins in blood serum that respond to invasion by foreign antigens and that protect the host by removing pathogens; an antibody.
the GNU version of the Collaborative International Dictionary of English
n. any one of a class of globular proteins which are antibodies and are produced by the immune system in animals.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a class of proteins produced in lymph tissue in vertebrates and that function as antibodies in the immune response
Word Usage
"IgE allergic reactions are immediate; after being exposed to the food, your body quickly overproduces what is called immunoglobulin E antibodies, or IgE."