IMPLICATIONS FOR THE ASSAY AND BIOLOGICAL-ACTIVITY OF INTERLEUKIN-4 -RESULTS OF A WHO INTERNATIONAL COLLABORATIVE STUDY

Five ampouled preparations of interleukin-4 (IL-4) have been evaluated by 36 laboratories in 14 countries for their suitability to serve as an international standard for this material in a joint international c ollaborative study for interleukin-3 (IL-3) and IL-4, The preparations were assayed in a wide range of in vitro bioassays and immunoassays, It is clear from the study that different recombinant preparations of IL-4 call have very different biological specific activities, includin g those from the same source (i.e., E. coli), In addition, immunoassay estimates of IL-4 levels did not correlate with those of bioassays, i llustrating the fact that immunoassays do not necessarily measure biol ogically active cytokine, It is of interest that the estimates provide d by the different bioassays were less variable than those produced by the immunoassays, suggesting that bioassays can be as accurate, if no t more so, than immunoassays, The large reduction in the variability o f estimates with the inclusion of a single reference preparation clear ly illustrates the need for a single standard to assay IL-4, On the ba sis of the results reported here, with the agreement of the participan ts of the study and with the authorisation of the Expert Committee on Biological Standardization (ECBS) of the World Health Organization (WH O) the preparation of IL-4 (88/656) was established as the internation al standard for interleukin-4 with an assigned unitage of 1000 IU/ampo ule.