Human IL-15 Synthetic Peptide. IL-15 (Interleukin 15 ) is a cytokine that regulates T and natural killer cell activation and proliferation. IL-15 and IL-2 share many biological activities as both have been found to bind common hematopoietin receptor subunits, and may compete for the same receptor, and thus negatively regulate each other's activity. The number of CD8+ memory cells is shown to be controlled by a balance between IL-15 and IL-2. IL-15 induces the activation of JAK kinases, as well as the phosphorylation and activation of transcription activators STAT3, STAT5, and STAT6. In mouse, studies suggest that IL-15 may increase the expression of apoptosis inhibitor Bcl-xL, possibly through the transcription activation activity of STAT6,