Inhibitors regulate interleukin-2 synthesis of stimulated lymphocytes: consequence for production procedures

The lymphokine interleukin-2 (IL-2) was produced in murine or human lymphocyte cultures by stimulation with concanavalin A (Con A) or phytohemagglutinin (PHA). IL-2 activity in the culture supernatant usually reached an optimum after 20-24 h, followed by a decrease at later times. The duration of IL-2 release was found to be limited by low molecular weight inhibitory substances. These substances reversibly inhibited further IL-2 release at later times. It could be excluded that IL-2 yields in vitro were primarily limited by protease action, inactivation of the mitogen, consumption of nutrients, "product inhibition" by IL-2 or by suppression through cell/cell interaction with hypothetic suppressor cells. It was also excluded that IL-2 activity in the culture supernatant was more quickly consumed by its target cells, the T blasts, than released by its producing cells. To overcome the limitation of IL-2 release by inhibitors, a procedure of repeated induction was developed. Spleen cells or peripheral blood lymphocytes were restimulated several times for 20-24 h with fresh medium and mitogen. This procedure enhanced IL-2 production 2-5 fold compared to a single induction for 24 h.