Function
Interleukin 15 (IL-15) regulates T and natural killer (NK) cell activation and proliferation. Survival signals that maintain memory T cells in the absence of antigen are provided by IL-15. This cytokine is also implicated in NK cell development. In rodent lymphocytes, IL-15 prevents apoptosis by inducing an apoptosis inhibitor, BCL2L1/BCL-x(L). In humans with celiac disease IL-15 similarly suppresses apoptosis in T-lymphocytes by inducing Bcl-2 and/or Bcl-xL.
A hematopoietin receptor, the IL-15 receptor, that binds IL-15 propagates its function. Some subunits of the IL-15 receptor are shared in common with the receptor for a structurally related cytokine called interleukin 2 (IL-2) allowing both cytokines to compete for and negatively regulate each other's activity. CD8+ memory T cell number is controlled by a balance between IL-15 and IL-2. When IL-15 binds its receptor, JAK kinase, STAT3, STAT5, and STAT6 transcription factors are activated to elicit downstream signaling events.
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