Cytokines & Growth Factors - FAQs
Product Scientists at Cell Signaling Technology (CST) make exceptional customer service and support their priority. Cytokines are produced and bio-assayed in-house as are our antibodies. The scientists who develop and assay these reagents are available as technical resources to our customers. These scientists can be contacted directly and will personally provide technical assistance to you, our customer.
- Applications across species: Do human cytokines work in mouse?
Some do, however, most do not or have a much higher ED50 on cells of another species. CST produces both human and mouse recombinant proteins.
- Should I be using proteins with or without carrier protein?
CST’s cytokines and growth factors are lyophilized and supplied with 20 µg BSA per 1 µg cytokine (With Carrier) or without added protein (Carrier free). Bovine Serum Albumin (BSA) carrier minimizes adsorption to surfaces and maximizes recovery upon reconstitution. Cytokines with carrier are generally used for tissue culture applications. Carrier free cytokines are generally used in animal research or in other procedures where BSA could interfere.
- Do different cytokines need different reconstitution buffers?
Due to differences between proteins, specific buffers are tested and recommended for reconstitution. If the indicated buffer is not used, the protein may not completely solubilize.
- How should I prepare 20 mM citrate, pH 3.0?
To prepare 20 mM Citrate Buffer, pH 3.0, dissolve the appropriate amount of citric acid in deionized H2O, adjust the pH to 3.0 with NaOH, and sterile-filter through 0.2 µM filter. For example, for 100 ml, dissolve 0.384 g citric acid (anhydrous) in 90 ml of deionized H2O, then adjust pH with a few drops of 5M NaOH. Once pH is 3.0, bring the volume up to 100 ml with DI water.
- Why are some products offered as liquids?
As part of our Quality Assurance, all bottled lots are bioassayed prior to their release for sale. This ensures that the bottled protein has full bioactivity and amount. Some cytokines lose bioactivity when lyophilized. For instance, Human Interferon-γ (hIFN-γ) #8901, Human Latent TGF-ß1 #5154, and Mouse FGF basic #5414 are sold in solution.
- What is the ED50 and how does it relate to units?
The ED50 is defined as the concentration of cytokine or growth factor required to elicit half the maximum biological response. The ED50 of a cytokine is generally referred to as 1 Unit.
- Why is the ED50 reported as a range?
Many cell-based assays exhibit assay to assay variation that is independent of the inherent biological activity of the protein. The ED50 range is derived from multiple independent assays of a given lot. This range then defines the bioactivity specifications for future lots. New lots are always assayed side by side with previous lots to ensure consistency and control for assay to assay variability.
- What is the specific activity and how is it determined?
Specific activity (expressed in units/mg) is a function of cytokine or growth factor purity and appropriate protein folding. To determine the specific activity, typically the readout of cytokine treatment is measured in a standardized bioassay. The ED50 (expressed in ng/ml), which is the concentration of cytokine or growth factor required to induce half the maximal biological response is determined in the assay.
The following formula can be used to convert the activity as an ED50 in ng/ml to specific activity in units/mg is:
Specific activity (units/mg) = 10E6 / ED50 (ng/ml)
- What are international units and how do they relate to our products?
Independent measurements of the biological activity of a specific protein may vary due to differences in bioassay systems and cell culture conditions between laboratories. In order to standardize the measurement of many cytokines and growth factors, the World Health Organization (WHO) and National Institute for Biological Standards and Control, UK (NIBSC) produce batches of protein with assigned biological activity against which the activity of various cytokine preparations can be tested. The purpose of this effort is to provide an international “gold standard” for testing and manufacturing biological therapeutics.
In order to calculate the IU of a cytokine, the cytokine must be assayed side by side with an NIBSC standard.
CST offers cytokines and growth factors sold by weight and not IU. We are not assaying our cytokines against the NIBSC standards at this time.