Description
The IL-2 receptor system consists of three non-covalently linked subunits termed IL-2Rα, IL-2Rβ, and IL-2Rγ. The IL-2Rα is a type I transmembrane protein consisting of a 219 amino acid (a.a.) extracellular domain, a 19 a.a. transmembrane domain and a 13 a.a. intracellular domain, which is not involved in the transduction of IL-2 signal. Activated T cells, regulatory T cells (Tregs) and NK cells express high levels of CD25 and expression of the high-affinity IL-2Rα is mostly limited to these cell populations. Signaling via IL-2Rα mediates multiple biological processes in various cell populations, e.g. proliferation and differentiation of B cells and NK cells. A soluble form of IL-2Rα (IL-2Rα) appears in serum, concomitant with its increased expression on cells. The function of the soluble IL-2Rα is unclear. Increased levels of IL-2Rα in biological fluids reportedly correlate with increased T and B cell activation and immune system activation. Increased serum concentration of IL-2Rα has been observed in patients with a variety of inflammatory conditions and in the course of some leukemias and lymphomas.