IL2R

IL2R, or interleukin-2 receptor, is a cytokine receptor that binds interleukin-2. It exists in multiple subunit configurations and is composed of IL2RA (CD25), IL2RB (CD122), and IL2RG (CD132). The high-affinity receptor is a trimer of α, β, and γ chains; the β/γ heterodimer forms an intermediate-affinity receptor; a low-affinity binding site can be formed by IL-2Rα alone, which does not signal.

Signal transduction proceeds primarily via JAK-STAT pathways, with JAK1 associated to IL2RB and JAK3 to IL2RG; activated STAT5 translocates to the nucleus to drive gene expression promoting T cell proliferation and effector functions. Additional pathways such as PI3K-Akt and Ras-MAPK may be engaged.

Expression pattern: the high-affinity IL-2 receptor is expressed on activated T cells and regulatory T cells (which constitutively express IL2RA). The shared gamma chain is used by other cytokine receptors, including IL-4, IL-7, IL-9, IL-15, and IL-21.

Clinical relevance: IL2RG mutations cause X-linked severe combined immunodeficiency (X-SCID). IL2RA (CD25) serves as a marker of T cell activation and regulatory T cells; blockade of IL-2/IL2R signaling with anti-CD25 antibodies has been explored in transplantation and autoimmune diseases; daclizumab was used for multiple sclerosis but was withdrawn from the market due to safety concerns. Therapeutically, recombinant IL-2 (aldesleukin) can boost immune responses in certain cancers but requires careful dosing to balance effector T cell and regulatory T cell effects.