Interleukin 2 receptor (IL-2R) is a heterotrimeric protein expressed on the surface of certain immune cells, such as lymphocytes, that binds and responds to the cytokine IL-2.IL-2R consists of three chains: an alpha chain (IL-2Rα/CD25), a beta chain (IL-2Rβ/CD122), and a gamma chain (IL-2Rγ/CD132). Of these, the α chain binds IL-2 with low affinity, whereas the β and γ chains form a complex that binds IL-2 with medium affinity.IL-2 and its receptor play an important role in the immune system, tolerance, and immunity primarily through direct action on T cells. However, the function of soluble IL-2Rα (sIL-2Rα) is unknown because its low affinity inhibits IL-2 binding. In any case, elevated sIL-2Rα levels in body fluids are associated with increased T and B cell activation and immune system activation. Monitoring serum levels of sIL-2Rα provides more detailed insights into some pathologies such as rheumatoid arthritis, systemic lupus erythematosus (SLE), certain leukemias, and lymphomas.