- 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.
- the fraction of the blood serum containing antibodies.
- an antibody. Abbreviation: Ig
- any of five classes of proteins, all of which show antibody activity. The most abundant ones are immunoglobulin G (IgG) and immunoglobulin A (IgA)