IL-15 is 14-15 kDa, a member of the four alpha-helical bundle family of cyto kines. It is very similar to IL-2, except that IL-15 has a IL-15 alpha receptor subunit 1. It play an important role in the growth and differentiation of T and B lymphocytes, natural killer cells, macrophages, and monocytes as well as it activates a number of importatnat intracellular signaling molecules 2. This implies that IL-15 could be essential for the immune responses, allograft rejection, and the pathogenesis of autoimmune d iseases 3.