IL15 (114 amino acids) is a cytokine that regulates T and natural killer cell activation and proliferation. It has a predicted molecular mass of approximately 12.5 kDa. Human IL15 shares approximately 97% and 73% amino acid sequence identity with simian and mouse IL15，respectively. Both human and simian IL15 are active on mouse cells. IL15 was initially isolated from the simian kidney epithelial cell line CV1/EBNA. It has also been isolated from mouse and human cell sources. The cytokines IL15 and IL2 share many biological properties and stimulatory activities (T，B，and NK cells). Both IL15 and IL2 stimulate mouse CTLL2 cells. In activated peripheral blood T lymphocytes，IL2 is highly expressed but the expression of IL15 is not detectable. There is no sequence homology between IL15 and IL2，though computer modeling indicates both possess a four alpha helical bundle structure. IL15 competes for binding sites with IL2，as both IL2 and IL15 stimulate the growth of cells through the IL2 receptor. IL15 mRN