Induction of cytotoxic T cell function requires sequential action of three different lymphokines.

Activation of resting Ly-2’ precursor T cells to cytotoxic T lymphocytes (CTL)’ requires stimulation by antigen or mitogen in combination with soluble mediators (1 -3). One of these antigen-nonspecific mediators is interleukin 2 (IL 2). IL 2 is released by activated Ly-l+ helper T cells and was distinguished to provide the proliferative signal (4, 5). It was only recently discovered that IL 2 is not the only helper factor required for the cytotoxic response (4-12). In this report, we provide evidence that three different, previously described activities (1 2) are sequentially required in distinct phases of the cytotoxic response. Absorption of Con A-induced spleen cell supernatants (Con A-Lk) on IL 2dependent T cell line cells removes the IL 2 activity, but a factor remains that is required through the first 48 hr of culture and is referred to as T cell cytotoxicity-inducing factor 1 (TCF1) in this report. Another factor is only required in the last 48 hr of culture and is called TCF2. Its activity can be destroyed in Con A-Lk by dialysis at pH 2, a treatment that leaves IL 2 titers unchanged (10-12). It is different from TCFl because it is also present in phorbol myristic acetate-activated EL-4 thymoma cell supernatants that lack TCF1. IL 2 is the third factor and is required at least in the early phase.