Interleukin 15 (IL15) is a widely expressed cytokine that is structurally and functionally related to IL2, which plays an important role in many immunological diseases. IL15 also regulates?T?and?natural killer?(NK) cell activation and proliferation. The activity of recombinant pig IL15 was measured in a cell proliferation assay using MO7e human megakaryocytic leukemic cells. MO7e cells were seeded into triplicate wells of 96-well plates at a density of 30,000 cells/well in RPMI-1640 with the addition of various concentrations of rpIL15. After incubated for 72h,?cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10 μl of CCK-8 solution was added to each well of the plate, then the absorbance at 450 nm was measured using a microplate reader after incubating the plate for 1-4 hours at 37 °C. Cell proliferation of MO7e cells after incubation with rpIL15 for 72h observed by inverted microscope was shown in Figure 1. The dose-effect curve of rpIL15 was shown in Figure 2. It was obvious that rpIL15 significantly promoted cell proliferation of MO7e cells .The EC50 for this effect is typically 0.55 ug/ml.