Procedure for titration of interleukin-2 based on direct observation of factor-dependent growth of cells

A semi-quantitative procedure for titration of interleukin-2 (IL-2) without the use of radioactive labeling of IL-2 target cells was developed. The procedure is based on the observation that those cells cultivated in round-bottom wells formed visible cultures and that the dimension of these cultures decreased at higher dilutions of IL-2 in the medium. The end-point of the titration can be easily established by observing the cultures with a concave mirror placed under the titration plate. The procedure has been used for the determination of IL-2 during its purification and characterization.