any of several classes of structurally related proteins that function as antibodies or receptors and are found in plasma and other body fluids and in the membrane of certain cells. Compare IgA, IgD, IgE, IgG, and IgM.
the fraction of the blood serum containing antibodies.
immunoglobulin im·mu·no·glob·u·lin (ĭm'yə-nō-glŏb'yə-lĭn, ĭ-myōō'-) n. Abbr. Ig Any of a group of large glycoproteins secreted by plasma cells in vertebrates that function as antibodies in the immune response by binding the specific antigens.