The conditions for the production of a T cell growth factor (TCGF or IL-2) capable of maintaining the long-term growth of activated lymphocytes and present in the supernatants of mouse stimulated EL-4 thymoma cells were investigated. IL-2 was induced in spleen cells and various T cell lines stimulated with T cell lectins and/or PMA (phorbol-12-myristate-13-acetate). The kinetics of IL-2 production by EL-4 cells were highly dependent on the cellular concentrations, concentration of serum, and inducers in the culture media, and especially incubation time.
The maximum activity of IL-2 appeared in the early phase with high cell concentration and in the late phase with low concentration of cells.
The kinetic study of IL-2 production in EL-4 cells demonstrated the maximum activity of IL-2 at 24hr incubation and the subsequent dramatic decrease was observed in the late phase of the culture.
The rate of IL-2 production also appeared in the same pattern. The arrest of IL-2 activity in the late phase seemed to be due to plausible types of regulatory mechanism ; the depletion of some essential components in the induction system, feedback inhibition by IL-2 formed in the early phase of the culture, and IL-2 absorption by EL-4 cells in the different phase of the culture.
The possible regulatory factors will be discused.