# Idiotype

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> Source: https://en.wikipedia.org/wiki/Idiotype
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{{Short description|Variable region of an antibody or a T-cell receptor}}
{{no footnotes|date=January 2014}}
thumb|The idiotype is based upon the variable region (labeled VL and VH in the diagram.)
In [immunology](/source/immunology), an '''idiotype''' is a shared characteristic between a group of [immunoglobulin](/source/immunoglobulin) or [T-cell receptor](/source/T-cell_receptor) (TCR) molecules based upon the [antigen](/source/antigen) binding specificity and therefore structure of their [variable region](/source/Fragment_antigen-binding). The variable region of antigen receptors of [T cell](/source/T_cell)s (TCRs) and [B cell](/source/B_cell)s (immunoglobulins) contain [complementarity-determining region](/source/complementarity-determining_region)s (CDRs) with unique [amino acid](/source/amino_acid) sequences. They define the surface and properties of the variable region, determining the antigen specificity and therefore the idio'''tope''' of the molecule. Immunoglobulins or TCRs with a shared [idiotope](/source/idiotope) are the same idio'''type'''. Antibody idiotype is determined by:
*Gene rearrangement
*Junctional diversity
*P-nucleotides (palindromic nucleotides at sites of single-strand breaks)
*N-nucleotides
*Somatic hypermutations

==Etymology and usage==
The word idiotype comes from two Greek roots, ''idio'' meaning 'private, distinctive, peculiar' and ''typos'' 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 when [Niels Jerne](/source/Niels_Jerne) formulated his [immune network theory](/source/immune_network_theory). Jerne was awarded the [Nobel Prize in Physiology or Medicine](/source/Nobel_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, where [epitope](/source/epitope) means an antigenic determinant. He also defined the "[paratope](/source/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 the [symmetrical network theory](/source/Immune_network_theory), in which the distinction between idiotype and paratope plays no role.

==See also==
* [Allotype (immunology)](/source/Allotype_(immunology))
* [Isotype (immunology)](/source/Isotype_(immunology))
* [Immune network theory](/source/Immune_network_theory)

==External links==
* {{MeshName|Immunoglobulin+idiotypes}}
* [http://pathmicro.med.sc.edu/mayer/IgTypes2000.htm Overview] at [Medical University of South Carolina](/source/Medical_University_of_South_Carolina)
* [https://web.archive.org/web/20070409180619/http://www.cehs.siu.edu/fix/medmicro/igs.htm Overview] at [Southern Illinois University Carbondale](/source/Southern_Illinois_University_Carbondale)

{{Immune system}}

Category:Immune system

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Adapted from the Wikipedia article [Idiotype](https://en.wikipedia.org/wiki/Idiotype) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Idiotype?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.