Coproduction of interleukin-2 and interferon-gamma in human mononuclear cells

Interleukin-2 (IL-2) and immune interferon (IFN-gamma) production was studied in Ficoll-hypaque purified human mononuclear cells derived from plateletpheresis residues. As previously reported, costimulation by 5 ng/ml of 12-O-tetradecanoylphorbol-13-acetate (TPA) and 5 microgram/ml of phytohemagglutinin (PHA) caused a marked enhancement of IFN-gamma levels compared to the yields obtained with PHA alone. IL-2 levels were also increased 50-300 times by this induction protocol. Mezerein (MZN), a compound structurally related to TPA, was found to be similar to TPA in enhancing IFN-gamma and IL-2 levels. In addition to TPA and MZN, four other related phorbol esters caused a stimulation of IFN-gamma and IL-2, with the production of IL-2 paralleling the production of IFN-gamma. Kinetic experiments indicate that low levels of IL-2 first became detectable 6 h after induction, whereas IFN-gamma could be demonstrated only later. Furthermore, IL-2 production reached a plateau earlier than IFN-gamma production in the TPA/PHA treated cultures. Dialysis at pH 2 abrogated the IFN-gamma activity but not the IL-2 activity. A three-step purification procedure developed for IFN-gamma isolation effectively separated IFN-gamma from IL-2. Our results show that there is a close correlation between the magnitude of IL-2 and IFN-gamma production under the experimental conditions employed. Physical separation of the two lymphokines is important for future studies on the interactions between IFN-gamma and IL-2 in various cellular immune reactions.