Granulocyte-macrophage colony-stimulating factor (GM-CSF), also known as colony-stimulating factor 2 (CSF2), is a monomeric glycoprotein that functions as a cytokine. it is a white blood cell growth factor. GM-CSF also has some effects on mature cells of the immune system. These include, for example, inhibiting neutrophil migration and causing an alteration of the receptors expressed on the cells surface. Besides, the proliferation of TF-1 cell line GM-CSF basic-dependent, thus, the activity of GM-CSF is usually measured by a cell proliferation assay using TF-1 cells. TF-1 cells were seeded into triplicate wells of 96-well plates with various concentrations of recombinant rat GM-CSF. After incubated for 3 days,?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 ℃. Proliferation of TF-1 cells after incubation with GM-CSF for 3 days observed by inverted microscope was shown in Figure 1. Cell viability was assessed by CCK-8 (Cell Counting Kit-8 ) assay after incubation with recombinant rat GM-CSF for 3 days. The result was shown in Figure 2. It was obvious that GM-CSF significantly increased cell viability of TF-1 cells. The ED50 is 0.06 ug/ml.