Cytokines and cell culture reagents

Questions & answers

How do I reconstitute and store MACS Cytokines?

MACS Cytokines are provided as lyophilized products. Follow the instructions in the product data sheet to reconstitute a vial of MACS Cytokines. Upon reconstitution, store working aliquots at -20° C or below, and avoid repeated freeze-thaw cycles. Shipment or shortterm storage of the lyophilized products at room temperature will not alter the performance.

What it the biological activity of a cytokine?

The biological activity of a cytokine is determined by an assay that measures the effect of the cytokine on factor-dependent cell lines or primary cells. Typical assays are induction or inhibition of cell proliferation. Biological activity is usually expressed as ED50 or units/mg (U/mg). If the bioassay is calibrated versus a certified NIBSC international standard protein, the activity is expressed in International Units/mg (IU/mg).

How important is the biological activity?

It is important to calculate how many active units of cytokine are available in the product. The most precise and reliable way to add a recombinant cytokine in your cell culture is to dose units/mL (U/mL) instead of ng/mL. This will increase the reproducibility of your experiments.

Where can I find the biological activity of a MACS Cytokine?

The minimal biological activity of any MACS Cytokine can be found in the product data sheet. The lot-specific biological activity of a premium-grade and GMP-grade cytokine is indicated in the Certificate of Analysis (CoA), available by request from Miltenyi Biotec technical support.

How do I calculate the biological activity in U/mg from the ED50 values?

Our product data sheet provides both values. However, you can also calculate the value using the simple formula:

How do I know how many U/mL are available in a MACS Cytokine product after reconstitution?

To calculate how many U/mL are available in a MACS Cytokine vial after reconstitution, you need to know the concentration of your vial after reconstitution, and the specific biological activity of the cytokine. Use these values in the formula:

My current protocol indicates a cytokine concentration in ng/mL. How do I convert it to U/mL?

To calculate how many U/mL correspond to the ng/mL of your protocol, you need to know the specific biological activity of the cytokine. Use the value in the formula:

Once you have calculated the concentration in U/mL, we suggest you to use the same concentration in U/mL for subsequent experiments.

How can I compare biological activities of products from different vendors?

Biological activities of products from different vendors can only be compared if the cellular assays are normalized with a defined international standard (from the NIBSC), or if the samples are measured in parallel using the same assay, the same batch of cells, and the same set of conditions.
The determined biological activity is only an indication for the sensitivity of the respective assay. It does not mean that this specific activity translates 1 : 1 into any particular application. Therefore, it is recommended to determine the optimal concentration for a specific application by a dose-response experiment.

How should I handle and store functional-grade antibodies?

Functional-grade antibodies are supplied in phosphate-buffered saline (PBS), pH 7.2. The product contains no preservative and is sterile filtered. Store protected from light at 2–8 °C. Do not freeze.
Always handle under aseptic conditions and dilute in sterile filtered buffer or medium, prior to use in cell culture.

What is the difference between a pure antibody and a pure functional-grade antibody?

Pure antibodies are unconjugated antibodies supplied in buffer containing stabilizer and 0.05% sodium azide. Pure antibodies are usually required for applications such as analysis of cellular markers using flow cytometry or immunofluorescence. Pure functionalgrade antibodies are sterile-filtered unconjugated antibodies containing no preservative and supplied in phosphate-buffered saline (PBS), pH 7.2. All functional-grade antibodies are tested for low endotoxin for optimal application in cell culture.

What are common applications of biotin-conjugated functional-grade antibodies?

Functional-grade antibodies are supplied in two forms: pure and biotin-conjugated. Biotin-conjugated functional-grade antibodies can be loaded onto Anti-Biotin MACSiBead™ Particles. These cellsized particles can conveniently be used for activation and expansion of a variety of primary cells.

How can I get my antibody of interest in pure functional-grade format, if it is not listed here?

All off-the-shelf antibodies, available either in fluorochromeconjugated or pure format, can be ordered in pure functional-grade format through our custom antibody service. For more information, visit

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