Overexpression of interleukin-2 (IL-2) and/or its receptor (IL-R) has been causally related to some malignancies, autoimmune disease, and graft rejection (1). There have been numerous efforts to find immunosuppressive agents through many kinds of experiments using cytokine-producing T cells, Jurkat cells, and EL4 cells (2-5). But only a few compounds, such as cyclosporin A (CsA) and FK506 have been identified until now to be powerful suppressors of the immune T cell system (8 -10). For detection of IL-2 production, isotope-labeled enzymelinked immunosorbent assay and IL-2 reporter gene assay have frequently been used (6, 7). However, these methods are biohazardous, very costly, and nonspecific. Moreover, in most of the inhibitor screening systems against lymphokine expression, the most severe drawback has been the cytotoxicity to target T cells due to the long-term treatment (over 24 h) with test samples. To reduce this toxic effect, a very small amount of diluted samples should be applied to the target cells, consequently causing the loss of a change to find a real inhibitor that is present at a very low level in a sample.
This paper describes a new method that overcomes sample cytotoxicity by shortening the duration of sample treatment in cytokine-producing T cells, confirming the method with CsA and FK506, which are known to be very potent inhibitors of IL-2 production. It has been reported that EL4 thymona cells produce IL-2 in response to phorbol 12-myristate 13-acetate (PMA) stimulation . This observation was confirmed by the experiment in which there is a dose-dependent increase in IL-2 production by PMA treatment of EL4 cells for 24 h (Fig. ). The maximal increase of IL-2