Editing Interleukin 2 (section)

== IL-2 receptor  ==

IL-2 is a member of a specific family of cytokines, each member of which has a [[Helix bundle#Four-helix bundles|four alpha helix bundle]]; this cytokine family also includes [[Interleukin-4|IL-4]], [[Interleukin 7|IL-7]], [[Interleukin 9|IL-9]], [[Interleukin 15|IL-15]] and [[Interleukin 21|IL-21]]. IL-2 signals through a [[IL-2 receptor]], a complex consisting of three chains, termed alpha ([[IL2RA|CD25]]), beta ([[IL2RB|CD122]]) and [[Common gamma chain|gamma]] ([[Common gamma chain|CD132]]). The gamma chain is common to all family members.<ref name="Liao_2011">{{cite journal | vauthors = Liao W, Lin JX, Leonard WJ | title = IL-2 family cytokines: new insights into the complex roles of IL-2 as a broad regulator of T helper cell differentiation | journal = Current Opinion in Immunology | volume = 23 | issue = 5 | pages = 598–604 | date = October 2011 | pmid = 21889323 | pmc = 3405730 | doi = 10.1016/j.coi.2011.08.003 }}</ref>

The IL-2 receptor (IL-2R) α subunit binds IL-2 with low affinity (K<sub>d</sub>~ 10<sup>−8</sup> M). Interaction of IL-2 and CD25 alone does not lead to signal transduction due to its short intracellular chain but has the ability (when bound to the β and γ subunit) to increase the IL-2R affinity 100-fold.<ref name=":1">{{cite journal | vauthors = Wang X, Rickert M, Garcia KC | title = Structure of the quaternary complex of interleukin-2 with its alpha, beta, and gammac receptors | journal = Science | volume = 310 | issue = 5751 | pages = 1159–63 | date = November 2005 | pmid = 16293754 | doi = 10.1126/science.1117893 | bibcode = 2005Sci...310.1159W | s2cid = 85394260 }}</ref><ref name=":0" /> Heterodimerization of the β and γ subunits of IL-2R is essential for signalling in [[T cell]]s.<ref name="Gaffen_2004">{{cite journal | vauthors = Gaffen SL, Liu KD | title = Overview of interleukin-2 function, production and clinical applications | journal = Cytokine | volume = 28 | issue = 3 | pages = 109–23 | date = November 2004 | pmid = 15473953 | doi = 10.1016/j.cyto.2004.06.010 }}</ref> IL-2 can signalize either via intermediate-affinity dimeric CD122/CD132 IL-2R (K<sub>d</sub>~ 10<sup>−9</sup> M) or high-affinity trimeric CD25/CD122/CD132 IL-2R (K<sub>d</sub>~ 10<sup>−11</sup> M).<ref name=":1" /> Dimeric IL-2R is expressed by memory CD8<sup>+</sup> T cells and [[NK cells]], whereas [[regulatory T cell]]s and activated T cells express high levels of trimeric IL-2R.<ref name=":0" />