Transforming Growth Factor Beta 1 (TGFB1) belongs to TGF-beta family. As a secreted protein and a cytokine, TGFB plays a role in the formation of blood vessels, the regulation of muscle tissue and body fat development, wound healing, and immune system function. Besides, TGFB1 regulates cell proliferation, differentiation, adhesion, migration by transducing the signal through transmembrane receptors type I and type II (TGFBR1 and TGFBR2). To test the effect of TGFb1 on inhibit IL4-dependent proliferation, CTLL-2 cells were seeded into triplicate wells of 96-well plates, the medium was 2% serum RPMI-1640 including various concentrations of recombinant human TGFb1. 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. Cell viability was assessed by CCK-8 assay. The result was shown in Figure1. It was obvious that TGFB1 significantly decreased cell viability of CTLL-2 cells. The ED50 of recombinant human TGFB1 is 2.91μg/mL.