IL2 (Interleukin-2) is a cytokine produced by T-cells in response to antigenic or mitogenic stimulation. IL2 is a type of signaling molecule in the immune system, that is required for both T-cell and B-cell proliferation and other activities crucial to regulation of the immune response. Recombinant human IL2 shares 56% AA sequence identity with mouse IL2, suggesting the exist of cross-species activity. Therefore, in order to detect the bioactivity of rhIL2, a cell proliferation assay has been conducted using CTLL-2 mouse cytotoxic T cells. Briefly, CTLL-2 cells were seeded into triplicate wells of 96-well plates at a density of 5,000 cells/well with or without the addition of various concentrations of IL2. After incubated for 48h, cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). 10µL of CCK-8 solution was added to each well of the plate, the absorbance at 450nm was measured using a microplate reader after incubating the plate for 1-4 hours at 37°C. Proliferation of CTLL-2 cells after incubation with IL2 for 48h observed by inverted microscope was shown in Figure 1.

The dose-effect curve of CTLL-2 was shown in Figure 2. It was obvious that CTLL-2 significantly promoted cell proliferation of CTLL-2 cells. The ED50 for this effect is typically 1.992 to 6.663 ng/mL.