Interferon-alpha (IFNa), also known as leukocyte interferon, represents a group of related but distinct proteins that share over 95% amino acid sequence homology. They are members of the type I interferon family which share a common cell surface receptor composed of two subunits. IFN-α has both anti-viral and immunomodulatory activities on target cells. To test the effect of IFNa on cell apoptosis, A549 cells were seeded into triplicate wells of 96-well plates at a density of 4,000 cells/well and allowed to attach overnight, then the medium was replaced with various concentrations of recombinant mouse IFNa diluted with 5% serum standard DMEM. 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 ℃. Apoptosis of A549 cells after incubation with IFNa for 72h 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 mouse IFNa for 72h. The result was shown in Figure 2. It was obvious that IFNa significantly decreased cell viability of A549 cells. The ED50 of recombinant mouse IFNa is 0.65 ug/ml.