In immunology, an idiotype is a shared characteristic between a group of immunoglobulin or T-cell receptor (TCR) molecules based upon the antigen binding specificity and therefore structure of their variable region.They define the surface and properties of the variable region, determining the antigen specificity and therefore the idiotope of the molecule.The term "idiotype" is sometimes used to describe the collection of multiple idiotopes, and therefore overall antigen binding capacity, possessed by an antibody.The word "idiotype" became influential in immunology when Niels Jerne formulated his immune network theory.Jerne was awarded the Nobel Prize in Physiology or Medicine in 1984 largely for being the father of immune network theory.