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Inimmunology, anidiotype is a shared characteristic between a group ofimmunoglobulin orT-cell receptor (TCR) molecules based upon theantigen binding specificity and therefore structure of theirvariable region. The variable region of antigen receptors ofT cells (TCRs) andB cells (immunoglobulins) containcomplementarity-determining regions (CDRs) with uniqueamino acid sequences. They define the surface and properties of the variable region, determining the antigen specificity and therefore the idiotope of the molecule. Immunoglobulins or TCRs with a sharedidiotope are the same idiotype. Antibody idiotype is determined by:
The word idiotype comes from two Greek roots,idio meaning 'private, distinctive, peculiar' andtypos meaning 'mark.' Thus, idiotype describes the distinctive sequence and region that makes any immunoglobulin/TCR unique from others of the same type which is its variable region.
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 whenNiels Jerne formulated hisimmune network theory. Jerne was awarded theNobel Prize in Physiology or Medicine in 1984 largely for being the father of immune network theory. He defined idiotype as the set of epitopes on the V region of an antibody molecule, whereepitope means an antigenic determinant. He also defined the "paratope" to be that part of an antibody variable region that binds to an antigen. The best developed version of immune network theory is called thesymmetrical network theory, in which the distinction between idiotype and paratope plays no role.