The IL-2 and IL-15 share many biological activities. They are found to bind hematopoietin receptor subunits, and may compete for the same receptor, thus negatively regulating each other’s activity. IL-2 is a secreted cytokine that regulates the proliferation of T and B lymphocytes. IL-15 regulates T and natural killer cell activation and proliferation.

The number of CD8+ memory cells is controlled by a balance between IL-2 and IL-15. The IL-2 receptor is a heterotrimeric protein complex whose gamma chain is also shared by interleukin 4 (IL-4) and interleukin 7 (IL-7). The IL-2 gene in mature thymocytes is monoallelic, which represents an unusual regulatory mode to control the gene expression precisely. The targeted disruption of a similar gene in mice leads to ulcerative colitis-like disease, which suggests an essential role of this gene in the immune response to antigenic stimuli. The IL-15 induces the activation of JAK kinases, as well as the phosphorylation and activation of transcription activators STAT3, STAT5, and STAT6. Studies of the mouse counterpart suggested that this cytokine may increase the expression of apoptosis inhibitor BCL2L1/BCL-x(L), possibly through the transcription activation activity of STAT6, and thus prevent apoptosis.