Fig. 1.

Interleukin (IL)-2 receptors. IL-2 is recognised by three types of receptor complex expressed on natural killer (NK) and T lymphocytes. The non-signalling, low-affinity receptor is composed of the IL-2Rα chain alone. The medium-affinity receptor is composed of the IL-2Rβ chain and the common γ chain. Finally, the high-affinity IL-2 receptor is composed of the IL-2Rα, the IL-2Rβ chain and the common γ chain. Ligand binding to the medium-affinity and high-affinity receptors leads to the phosphorylation of Janus kinase-1 (JAK1) and JAK3 and the recruitment and subsequent phosphorylation of signal transducer and activator of transcription-3 (STAT3) and STAT5, and ensuing transcriptional changes