IL‐15 signaling is an important factor in proliferating, activating, and immunomodulating primarily T cells. IL‐15R α is an IL‐15 specific, single pass membrane receptor which complexes with IL‐2R β and IL‐2R γ to form a high affinity IL‐15 receptor. Additionally, the IL‐15/IL‐15R complex is capable of binding to IL‐2 β/γ receptors on other cells, therefore enabling IL‐15 to indirectly activate cells expressing IL‐2 β/γ receptors. A soluble form of IL‐15 receptor α is naturally produced by proteolytic cleavage of the membrane‐bound precursor. This naturally occurring soluble form can act as a modulator of IL‐15 signaling through the inhibition of IL‐15 receptor binding. Recombinant Human sIL‐15 Receptor α Fc has a calculated molecular weight of 44.4 kDa protein and contains 408 amino acid residues, which consists of the extracellular domain of IL‐15R α fused to the Fc portion of human IgG. Due to glycosylation, it migrates at an apparent molecular weight of 50‐60 kDa, under reducing conditions.