IMPLICATIONS FOR THE ASSAY AND BIOLOGICAL PROPERTIES OF INTERLEUKIN-3- RESULTS OF A WHO INTERNATIONAL COLLABORATIVE STUDY

Five preparations of interleukin-3 (IL-3) have been evaluated by 28 la boratories in 12 countries for their suitability to serve as an intern ational standard for this material in a joint international collaborat ive study for IL-3 and interleukin-4 (IL-4). The preparations were ass ayed in a wide range of in vitro bioassays and immunoassays. It is cle ar from the biological assays contributed to this study that different recombinant preparations of IL-3 can have very different biological s pecific activities, including those from the same source (i.e., E. col i). Biological assays of IL-3 were significantly more consistent in th eir estimates of levels of IL-3 than the immunoassays, suggesting an u nusual pattern of epitope recognition amongst the antibodies included in the immunoassays. This study also illustrates the point that the le vel of cytokine measured by immunoassay does not necessarily reflect t he biological potency of the cytokine. On the basis of results reporte d here, with the agreement of the participants of the study and with t he authorisation of the Expert Committee on Biological Standardization (ECBS) of the World Health Organization (WHO) the preparation of IL-3 (91/510) was established as the international standard for interleuki n-3 with an assigned unitage of 1700 IU/ampoule.