A new non-radioactive method for IL-2 bioassay

An oxidation-reduction (redox) indicator, alamarBlue, was used to measure the bioactivity of interleukin 2 (IL-2). This assay system has several advantages over other bioassays for measuring IL-2. It is a nonradioactive method unlike the conventional tritium-labeled thymidine ([3H]TdR) incorporation assay. The alamarBlue assay is also easier to use than other colorimetric methods, such as the MTT assay, because the alamarBlue assay does not depend on the extraction of insoluble formazan salt, which is time-consuming, error-prone, and cumbersome. Due to its solubility in culture medium and its nontoxicity to cells, alamarBlue provides an easy method to monitor cellular growth using either a fluorescence- or an absorbance-based instrument. The alamarBlue assay is not sample-destructive, unlike the thymidine incorporation and MTT methods. This adds another advantage to the alamarBlue method as the measurement of cellular growth by sample-destructive methods requires as many tubes as time points whereas the alamarBlue method requires only one tube for the entire growth period. In this study, alamarBlue was used to measure the proliferation of the IL-2-dependent cytotoxic T cell line, CTLL-2. The colorimetric change of alamarBlue at 570 nm compared to the reference wavelength, 600 nm, was proportional to the number of viable cells. The sensitivity of the IL-2 assay using alamarBlue was comparable to that of the [3H]thymidine incorporation method. These results demonstrate that the alamarBlue assay is valid for the IL-2 bioassay and that alamarBlue can replace the [3H]thymidine employed in the conventional proliferation assays.