Leukemia inhibitory factor (LIF), is an interleukin 6 class cytokine that affects cell growth by inhibiting differentiation. LIF as a cytokine also has another fuction including: the growth promotion and cell differentiation of different types of target cells, influence on bone metabolism, cachexia, neural development, embryogenesis and inflammation. To evaluate the activty of recombinant rat LIF, the K562 cells were were seeded into triplicate wells of 96-well plates at a density of 5,000 cells/well with5% serum standard 1640  which contains various concentrations of recombinant rat LIF. 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 2-4 hours at 37 ℃. After incubation with LIF for72h, proliferative inhibition of K562 cells observed by inverted microscope was shown in Figure1. Cell viability was assessed by CCK-8(Cell Counting Kit-8 ) assay after incubation with recombinant LIF for72h. The result was shown in Figure2. It was obvious that LIF significantly inhibit cell viability of K562 cells. The ED50 is 1.44μg/ml.

Figure2. Proliferative inhibition of K562 cells after stimulated with LIF.