Human IL-2 exerts its biological effects via signaling through its receptor system,
IL-2R. IL-2 and its receptor (IL-2R) are required for T-cell proliferation and other
fundamental functions which are crucial of the immune response. IL-2R consists of 3
noncovalently linked type I transmembrane proteins which are the alpha (p55), beta (p75),
and gamma (p65) chains. The IL-2R alpha chain contains an extracellular domain of 219 amino acids,
a transmembrane domain of 19 amino acids, and an intracellular domain of 13 amino acids.
The secreted extracellular domain of IL-2R alpha (s-IL-2R-a), also called TAC-antigen,
is expressed on leukemia cells, lymphoma cells, approximately 10% NK cells, as well
as recently activated T and B cells. Recombinant human s-IL-2R-a is a 24.8 kDa protein
containing 219 amino acid residues consisting of only the extracellular domain of IL-2R alpha.
Due to glycosylation, IL-2R alpha has an approximate molecular weight of 31 kDa based on SDS-PAGE
gel and Mass Spectrometry.