A method for the quantitative analysis and standardization of interleukin-1 bioactivity

A method is presented for the reproducible quantitation of the biological activity of interleukin 1 (IL-1). This method provides diagnostic tools which give insights into the qualitative aspects of the binding of IL-1 and of the resulting activation of the responder thymocytes; for example, whether the lymphokine and/or the responder population is heterogeneous, or whether a threshold level exists. It establishes under what circumstances the assumptions on which it is based are reasonably adhered to and, consequently, quantitative estimation in the manner it prescribes is justified. It also gives a simple way to calculate both the maximal response attainable for each preparation in an assay and the dilution of a particular preparation that would produce a half-maximal response, the accepted unit of activity of IL-1. This empirical technique provides an improved means of comparing the activities of various preparations of IL-1 in bioassays using various stocks of responder cells and reagents. It should also be applicable to the evaluation of the biological activity of lymphokines in general.