How important is the biological activity of a cytokine?

 It is important to calculate how many active units of cytokine are available in the product. The most precise and reliable way to add recombinant cytokine to your cell culture is to dose units/mL (U/mL). This will increase the reproducibility of your experiments as compared to ng/mL dosing. Whenever possible, it is recommended to use units that were determined by a calibrated assay, because this will give you the highest reliability for reproducible results.

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Efficient cytokine usage with specific unit-dosing. Green arrows indicate concentration of cytokine input to reach maximum cellular response. Identical activity can be reached with cytokine concentrations of 100 IU/mL and 1000 IU/mL. Yellow and red arrows indicate insufficient cytokine input.