Definition
Interleukin 2 (IL‑2) is a cytokine signaling molecule produced primarily by activated T lymphocytes. It plays a central role in the regulation of white blood cell proliferation, differentiation, and survival, particularly in the adaptive immune response.
Overview
IL‑2 is secreted after antigen recognition by naïve CD4⁺ T cells and, to a lesser extent, by CD8⁺ T cells, natural killer (NK) cells, and dendritic cells. The cytokine binds to the interleukin‑2 receptor (IL‑2R), a heterotrimeric complex composed of α (CD25), β (CD122), and γ (common γ chain, CD132) subunits. High‑affinity IL‑2R expression is induced upon T‑cell activation, enabling autocrine and paracrine signaling that drives clonal expansion of antigen‑specific lymphocytes, promotes the development of regulatory T cells (Tregs), and enhances cytotoxic activity of NK cells. Recombinant IL‑2 is employed clinically in cancer immunotherapy (e.g., metastatic renal cell carcinoma and melanoma) and in investigations of immune modulation.
Etymology/Origin
The term “interleukin” derives from “inter‑” (between) and “leukine” (relating to leukocytes), reflecting its role as a signaling factor between white‑blood cells. Interleukin 2 was identified in the late 1970s as the first T‑cell growth factor, and the numeral “2” denotes its order of discovery within the interleukin family.
Characteristics
| Property | Details |
|---|---|
| Molecular weight | Approximately 15 kDa (monomer) |
| Structure | Four‑helix bundle cytokine; secreted as a soluble protein |
| Gene | IL2 gene located on chromosome 4q27 in humans |
| Receptor affinity | Low‑affinity (βγ) → intermediate (αβγ) → high‑affinity (αβγ) complexes |
| Biological activities | • Promotes proliferation of activated T cells • Supports differentiation of Tregs • Enhances NK‑cell cytotoxicity • Induces expression of IL‑2R α‑chain (CD25) |
| Clinical use | Recombinant IL‑2 (aldesleukin) for oncology; experimental agent in immunotherapy trials |
| Regulation | Expression induced by antigenic stimulation, costimulatory signals (e.g., CD28), and transcription factors NF‑κB and AP‑1; negatively regulated by cytokines such as IL‑10 and by suppressor of cytokine signaling (SOCS) proteins |
Related Topics
- Interleukin‑2 receptor (IL‑2R) – the heterotrimeric receptor complex mediating IL‑2 signaling.
- Regulatory T cells (Tregs) – a subset of CD4⁺ T cells whose development and maintenance are IL‑2‑dependent.
- Cytokine storm – hyperactive immune responses in which dysregulated IL‑2 may contribute.
- Aldesleukin – a recombinant form of IL‑2 used therapeutically.
- Other interleukins – e.g., IL‑4, IL‑6, IL‑10, which together orchestrate immune communication.
All information presented reflects current scientific consensus as of 2026.