Sustained IL-2 production by the EL4 subline during continuous phorbol diester stimulation is related to an increase of IL-2-mRNA

Abstract

The murine T lymphoma EL4 subline produces large amounts of interleukin 2 (IL-2) upon stimulation with phorbol myristate acetate (PMA). It was found to survive continuous PMA stimulation (10 ng/ml, renewed daily, at 10 6 cells/ml), and to maintain its IL-2 production for several days in a culture medium low in protein. IL-2 production varied from day to day with a peak within the first 2 days of stimulation. PMA stimulation was accompanied by morphologic changes (enlargement and adhesiveness), arrest in cell division and DNA replication, continued RNA synthesis and increased mitochondrial activity. These effects were reversible upon removal of PMA, with a decrease of IL-2 secretion to the background level and a progressive recovery of cell growth. The reverted EL4 cells were again able to produce large amounts of IL-2 upon restimulation with PMA. Growth of EL4 cells was shown not to depend on autologous production of IL-2, and their DNA synthesis could be arrested by aphidicolin without a concomitant accumulation of IL-2 in the supernatant. This indicates that the increase in the amount of free IL-2 is not simply due to reduced consumption by the EL4 cells themselves. PMA appears to act at the level of the expression of the IL-2 gene, since IL-2 mRNA was much more abundant in the IL-2-secreting PMA-treated cells than in untreated controls. Our observations show that considerable amounts of IL-2 can be obtained from a single EL4 cell inoculum and may represent an original model to study the effects of PMA on the differentiation and maturation processes cells.