Screening of interleukin-2 production inhibitor with mouse thymoma EL4 cells.

Sir: Human interleukin-2 (IL-2) regulates many essential immune functions, but its overexpression is causally related to malignancy, autoimmune disease and renal allograft rejection1-3). In order to find immunosuppressants, isotopelabeled enzyme-linked immunosorbent assay (ELISA) and IL-2 reporter gene assay are used to detect IL-2 production, and cyclosporin A (CsA) and FK506 have been found to be powerful IL-2 inhibitors4-6). However, these methods are biohazardous, very costly and nonspecific. Moreover, the long-term treatment (over 24 hours) with test samples is cytotoxic to target T cells. Therefore, we developed a modified method that minimizes this toxic effect by shortening the duration of sample treatment in mouse thymoma EL4, a cytokineproducing T cell line, and also maximizes the amount of test sample applied to the target cells through introduction of a washing step to increase the likelihood of finding a real inhibitor, which might be present at very low concentrations. When culture broth of actinomycetes was applied to EL4 cells for more than 25 minutes, there was a significant decrease in EL4 cell viability. But the cytotoxic