Recombinant Human IL-15 ELISA Standard

Laboratory units are the actual values obtained from running an assay with a particular protein in an assay in your lab; i.e., the activity (ED50) you observe on your target cells. ‘International' units are consensus values of potency derived from a collaborative NIBSC effort to standardize reported use of proteins. These values are derived from bioassay testing of the same protein by many target cell types/substrains. It is very likely that the ‘laboratory' units you observe and the NIBSC values will not correlate 1:1; e.g., it might take 0.1 - 20 U/mL to see 1 U/mL in your experiment. These are bioassay standards describing potency in bioassay only. The mass values assigned to these are not hard values and use of these for immunoassay standardization is of limited value unless assays calibrated by the NIBSC standard use the same capture and detection antibody clones.

The formula for converting the activity as an ED50 in ng/ml to a specific activity in Units/mg is:
Specific activity (Units/mg) = 10e6/ ED50 (ng/mL)

A "unit" is defined as the concentration of protein required to induce half maximal activity (e.g. in ng/mL). This is also referred to as the ED50, or 50% effective dose. This method of expressing potency should only be used for proteins whose dose response curves are sigmoidal in shape (e.g., not chemotaxis assays).

You should store the recombinant proteins at or below -80 degrees C. The proteins can be diluted, and specific information regarding this is available on the Technical Data Sheets. However, key considerations are as follows:

- Always quick spin the vials prior to opening
- Dilute primary stock to a minimum of 10ug/mL
- Perform dilutions in a buffered saline (formulation on technical data sheet) which contains 1.0% BSA or 10% FBS as a protein carrier/stabilizer
- Make aliquots to minimize the number of freeze/thaw cycles. Avoid freezers with thermal cycling, such as frost free freezers.

In most cases, the recombinant proteins are offered at a concentration of 0.1 mg/mL, while the carrier free recombinant proteins are offered at 0.5mg/mL. However, we do recommend you refer to the product vial for lot specific information.