Interleukin-2 receptor high-affinity trimer (IL-2Rαβγ)

The high-affinity Interleukin-2 receptor (IL-2R) is a heterotrimeric protein complex composed of three distinct subunits: IL-2Rα (CD25), IL-2Rβ (CD122), and IL-2Rγ (CD132) [Malek, 2008]. While the dimeric IL-2Rβγ complex is found on many immune cells and has intermediate affinity for IL-2, the trimeric form is characterized by a 100-fold higher affinity, primarily due to the presence of the CD25 subunit [Boyman & Sprent, 2012]. Regulatory T cells (Tregs) constitutively express high levels of this trimeric receptor, which allows them to sense and respond to extremely low concentrations of IL-2 that are insufficient to trigger effector T cells or natural killer cells [Whang et al., 2018]. This signaling pathway is vital for the survival, stability, and suppressive activity of Tregs, making it a central pillar of peripheral immune tolerance [Spolski et al., 2018]. In therapeutic development, this receptor is targeted by low-dose IL-2 or engineered IL-2 muteins designed to selectively expand the Treg population for treating autoimmune diseases such as systemic lupus erythematosus and type 1 diabetes [Klatzmann & Abbas, 2015]. Conversely, blocking the alpha subunit with monoclonal antibodies can inhibit the formation of the high-affinity complex, thereby suppressing unwanted T cell activation in conditions like organ transplant rejection [Waldmann, 2006]. Modern drug discovery efforts focus on "Treg-biased" IL-2 variants that minimize interaction with the dimeric receptor on effector cells to reduce toxicity, such as vascular leak syndrome, and improve therapeutic index [Peterson et al., 2018]. This target represents a key node in immuno-oncology and autoimmune therapy, balancing the activation of suppressive versus effector immune responses.

Other names

CD25/CD122/CD132 complexHigh-affinity IL-2 receptorIL-2R alpha/beta/gamma heterotrimerTrimeric IL-2 receptorInterleukin-2 receptor high-affinity trimer on regulatory T cells

Selective agonism of the high-affinity trimeric receptor to expand regulatory T cells (Tregs) or antagonism of the alpha subunit (CD25) to inhibit T cell activation [Klatzmann & Abbas, 2015; Waldmann, 2006].