High-affinity interleukin-2 receptor complex (IL-2Rαβγ)

The high-affinity interleukin-2 receptor (IL-2R) complex is a heterotrimeric assembly consisting of the IL-2Rα (CD25), IL-2Rβ (CD122), and IL-2Rγ (CD132) subunits. While the dimeric βγ form has intermediate affinity, the inclusion of the α subunit creates a high-affinity site that allows cells to respond to very low concentrations of IL-2 (Liao et al., 2013, Immunity). This complex is primarily expressed on activated T-cells and is constitutively expressed on regulatory T-cells (Tregs), playing a vital role in driving T-cell expansion and maintaining immune tolerance (UniProt, P01589). In clinical medicine, the receptor is a major target for immunosuppression; for instance, antibodies blocking the CD25 subunit are used to prevent acute organ rejection in transplant recipients. Conversely, IL-2 agonists are employed in oncology to boost the immune response against metastatic melanoma and renal cell carcinoma by signaling through this complex. However, therapeutic use of IL-2 agonists is often limited by severe side effects such as capillary leak syndrome, which results from the activation of the receptor on vascular endothelial cells (StatPearls, 2023).

Other names

CD25/CD122/CD132 complexTrimeric interleukin-2 receptorIL-2R alpha/beta/gamma complexHigh-affinity IL-2R

Drugs targeting this complex act as either antagonists, agonists, or targeted toxins. Monoclonal antibodies like basiliximab bind to the CD25 subunit to competitively inhibit IL-2 binding, thereby preventing T-cell activation and proliferation in transplant settings (StatPearls, 2023). Agonists like aldesleukin mimic IL-2 to stimulate anti-tumor T-cell activity, while fusion toxins like denileukin diftitox use the receptor to internalize cytotoxic payloads into malignant cells (Malek, 2008, Annual Review of Immunology).